Mallory 4309 fpr vac/boost nipple question (boosted Nikki)
12-30-14, 02:09 PM
#51
Secondaries and the annoying delay (solved)
Success!! Finally!!
After several months and lots of testing later, the secondary bog/delay/hiccup/glitch that most of us have experienced with our boost prepped Nikkis has been solved!
Here are the numbers:
secondary main air bleed:
120
secondary fuel jet:
150
The delay is now gone at low and high RPM, under vacuum and in boost. It is even more powerful now breaking them loose on dry road on my test hill in 3rd gear! I've had to concentrate on keeping the car going straight so I haven't glanced at the wideband yet, but I think the air/fuel numbers are within the healthy range. The engine feels and sounds healthy, anyway.
And the nice part is the air bleeds and fuel jets are tunable to whatever the engine wants. For example if the 150s are a tad too lean, a set of 155s will fix it. Or if the 120 air bleeds are too small, a set of 125 or 130 can be swapped in*
*Sterling style air bleed mod with Holley .051" air bleeds (130 metric equiv) or any other size you need.
After several months and lots of testing later, the secondary bog/delay/hiccup/glitch that most of us have experienced with our boost prepped Nikkis has been solved!
Here are the numbers:
secondary main air bleed:
120
secondary fuel jet:
150
The delay is now gone at low and high RPM, under vacuum and in boost. It is even more powerful now breaking them loose on dry road on my test hill in 3rd gear! I've had to concentrate on keeping the car going straight so I haven't glanced at the wideband yet, but I think the air/fuel numbers are within the healthy range. The engine feels and sounds healthy, anyway.
And the nice part is the air bleeds and fuel jets are tunable to whatever the engine wants. For example if the 150s are a tad too lean, a set of 155s will fix it. Or if the 120 air bleeds are too small, a set of 125 or 130 can be swapped in*
*Sterling style air bleed mod with Holley .051" air bleeds (130 metric equiv) or any other size you need.
12-30-14, 02:35 PM
#52
Why 150 secondary fuel jets?
I discovered a turbo tune wants about ten numbers leaner than an NA tune. If stock is 160, then a turbo tune will want 150.
I first discovered this earlier in the year when I went from NA tuning to boost tuning on my first hogged out Nikki. The first primary jets were 140 which were kinda too rich for anything so I swapped in some 130s and it ran quite well with no secondary bog (NA). The secondary tune was still factory with 140 air and 160 fuel. However it went pig rich at cruise as soon as I swapped the turbo in. So I swapped in some 120 fuel jets in the primary side and left the secondaries alone. The result was acceptible primary AFRs of about 14 but the secondaries would have a bog/delay that got quite anoying.
I read something on the forum recently where coldy13 or shredduhh or possibly even Robert said the turbo wants a slightly leaner tune than NA. This of course contradicts what others like bad83 and LizardFC said about needing to tune richer for boost (Actually bad83 said to leave the primaries alone and only up the secondaries to #200 Mikuni jets which he said are different in their sizing scheme from the way Mazda did it, which I don't think is true. I think his #200 is the same as any other metric jet at 200 or 2.00mm. When I tried my drilled 208s, it fell on its face and the delay was at least 3 seconds so I aborted the test. So for me, bigger was NOT the answer).
The way I fixed the secondary bog was to fill in the secondary slow air bleeds #1 and #2 with solder, and then do a Sterling style mod to the secondary main air bleeds to accept a set of Nikki fuel jets or Holley air bleeds in the screw head at the top. I then had to decrease the size of the secondary fuel jets to compensate for the reduced air, because I was getting 10.0 on the wideband which is the richest it will read (not sure what the actual AFR might have been but probably 8 or 9.something with is just wasteful and could foul your plugs or lead to nasty carbon buildup on the rotor faces).
The end result is a 10% rule or formula that anyone can follow. A turbo tune likes about ten numbers less fuel. So if your hogged out Nikki runs best while NA with 130 primary and 160 secondary fuel jets, to use that same carb for boost, you will want to size both jets down by ten if metric (work out the number conversions if sticking with imperial measurements, duh) so you're left with 120 primary and 150 secondary fuel jets, or equivilant. The air bleeds need attention too, often requiring a few sizes smaller as well. Think of it this way: the turbo is forcing so much more air into the carb that it makes it work more effeciently, so it needs less air bleed and less fuel jet to accomplish the same thing. Or maybe the mallory has something to do with it. Probably both.
Of course all this is from a "it worked for me" perspective and if you blow up your engine following my advice, you've been warned ahead of time to tune your own stuff to what YOUR engine wants. Mine wanted 10 numbers less fuel on primaries and secondaries. Yours may want more (or less).
Oh I've also only tested this on one carb so far, but the results were so perfect I think the other three boost prepped carbs around here will want the modded sec air bleeds and 150 fuel jets too.
I first discovered this earlier in the year when I went from NA tuning to boost tuning on my first hogged out Nikki. The first primary jets were 140 which were kinda too rich for anything so I swapped in some 130s and it ran quite well with no secondary bog (NA). The secondary tune was still factory with 140 air and 160 fuel. However it went pig rich at cruise as soon as I swapped the turbo in. So I swapped in some 120 fuel jets in the primary side and left the secondaries alone. The result was acceptible primary AFRs of about 14 but the secondaries would have a bog/delay that got quite anoying.
I read something on the forum recently where coldy13 or shredduhh or possibly even Robert said the turbo wants a slightly leaner tune than NA. This of course contradicts what others like bad83 and LizardFC said about needing to tune richer for boost (Actually bad83 said to leave the primaries alone and only up the secondaries to #200 Mikuni jets which he said are different in their sizing scheme from the way Mazda did it, which I don't think is true. I think his #200 is the same as any other metric jet at 200 or 2.00mm. When I tried my drilled 208s, it fell on its face and the delay was at least 3 seconds so I aborted the test. So for me, bigger was NOT the answer).
The way I fixed the secondary bog was to fill in the secondary slow air bleeds #1 and #2 with solder, and then do a Sterling style mod to the secondary main air bleeds to accept a set of Nikki fuel jets or Holley air bleeds in the screw head at the top. I then had to decrease the size of the secondary fuel jets to compensate for the reduced air, because I was getting 10.0 on the wideband which is the richest it will read (not sure what the actual AFR might have been but probably 8 or 9.something with is just wasteful and could foul your plugs or lead to nasty carbon buildup on the rotor faces).
The end result is a 10% rule or formula that anyone can follow. A turbo tune likes about ten numbers less fuel. So if your hogged out Nikki runs best while NA with 130 primary and 160 secondary fuel jets, to use that same carb for boost, you will want to size both jets down by ten if metric (work out the number conversions if sticking with imperial measurements, duh) so you're left with 120 primary and 150 secondary fuel jets, or equivilant. The air bleeds need attention too, often requiring a few sizes smaller as well. Think of it this way: the turbo is forcing so much more air into the carb that it makes it work more effeciently, so it needs less air bleed and less fuel jet to accomplish the same thing. Or maybe the mallory has something to do with it. Probably both.
Of course all this is from a "it worked for me" perspective and if you blow up your engine following my advice, you've been warned ahead of time to tune your own stuff to what YOUR engine wants. Mine wanted 10 numbers less fuel on primaries and secondaries. Yours may want more (or less).
Oh I've also only tested this on one carb so far, but the results were so perfect I think the other three boost prepped carbs around here will want the modded sec air bleeds and 150 fuel jets too.
12-31-14, 01:27 AM
#53
I think you've stumbled (no pun intended) on something important here, but you may be looking at it the wrong way. Perhaps it's not that the carb wants less fuel with boost, but less air. Allow me to throw out a theory:
We know there's always a pressure differential between the top of the carb (float bowls, air horn, etc) and the bottom (plenum under the throttle plates). That's how the thing works. It's what causes both air and fuel to flow through all these jets, bleeds, and circuits. I think boost multiplies this differential. While both sides are in fact pressurized, there's a greater difference in pressure between the air pushing into the carb and the air flowing through the manifold. The more restrictive the carburetor, the greater this effect will be. That's why stock-bore venturis may not work so well in boosted applications. Sound good so far?
So what may be going on here is an effect of this multiplied differential under boost. More pressure up top forces air through the air bleeds at a faster rate than at atmospheric pressures. It may have a similar effect on fuel, but air is far more easily moved than liquid. With the circuit full of air, there's a limit to how much fuel can be drawn into it, no matter what size the jet. This may be why when I changed my secondary fuel jets from 195 to a massive 238, I saw only a small decrease (richer) in AFR under boost. I figured 238 jets would just dump liquid fuel into the airstream and cause the engine to bog when I leaned on the throttle. I was shocked when this wasn't the case.
Getting back to this multiplied pressure differential - with your typical mechanical secondary setup, the effect is going to be strongest before the secondary plates just start to open. At this time, boost is beginning to build but the nearly closed secondary plates are causing a lot of restriction, causing pressure to rise on the top side much faster than in the manifold. This is happening right as the secondary slow air bleeds are doing their thing. The increased pressure up top forces a ton of air through the slow air bleeds, leaning the mixture considerably and causing your hesitation. When you soldered your slow air bleeds shut, you eliminated this. Reducing the size of the main secondary air bleeds also helped keep this high pressure differential from leaning out your mixture under boost, which is the problem I am having. So I guess I know what I need to do next!
So yeah, I think you pretty much nailed it when you said the carb needs less air bleed to accomplish the same thing under boost. Although if you don't drastically reduce the size of the secondary air bleeds, you may not even need to fool with the fuel jets.
And another note on the hiccup when you hit boost: One thing I did to my carb was modify the linkage a bit so the secondaries open sooner, with less throttle. This means my slow bleeds are doing their thing before the pressure rises, and the main fuel circuit kicks in before boost does. You may want to give that a try. Just make sure the plates open fully right at WOT and not before, because those modified shafts can twist really easily.
By the way, I can't wait to see your numbers when you get the chance to do more tests. I'm curious what your AFR's look like.
We know there's always a pressure differential between the top of the carb (float bowls, air horn, etc) and the bottom (plenum under the throttle plates). That's how the thing works. It's what causes both air and fuel to flow through all these jets, bleeds, and circuits. I think boost multiplies this differential. While both sides are in fact pressurized, there's a greater difference in pressure between the air pushing into the carb and the air flowing through the manifold. The more restrictive the carburetor, the greater this effect will be. That's why stock-bore venturis may not work so well in boosted applications. Sound good so far?
So what may be going on here is an effect of this multiplied differential under boost. More pressure up top forces air through the air bleeds at a faster rate than at atmospheric pressures. It may have a similar effect on fuel, but air is far more easily moved than liquid. With the circuit full of air, there's a limit to how much fuel can be drawn into it, no matter what size the jet. This may be why when I changed my secondary fuel jets from 195 to a massive 238, I saw only a small decrease (richer) in AFR under boost. I figured 238 jets would just dump liquid fuel into the airstream and cause the engine to bog when I leaned on the throttle. I was shocked when this wasn't the case.
Getting back to this multiplied pressure differential - with your typical mechanical secondary setup, the effect is going to be strongest before the secondary plates just start to open. At this time, boost is beginning to build but the nearly closed secondary plates are causing a lot of restriction, causing pressure to rise on the top side much faster than in the manifold. This is happening right as the secondary slow air bleeds are doing their thing. The increased pressure up top forces a ton of air through the slow air bleeds, leaning the mixture considerably and causing your hesitation. When you soldered your slow air bleeds shut, you eliminated this. Reducing the size of the main secondary air bleeds also helped keep this high pressure differential from leaning out your mixture under boost, which is the problem I am having. So I guess I know what I need to do next!
So yeah, I think you pretty much nailed it when you said the carb needs less air bleed to accomplish the same thing under boost. Although if you don't drastically reduce the size of the secondary air bleeds, you may not even need to fool with the fuel jets.
And another note on the hiccup when you hit boost: One thing I did to my carb was modify the linkage a bit so the secondaries open sooner, with less throttle. This means my slow bleeds are doing their thing before the pressure rises, and the main fuel circuit kicks in before boost does. You may want to give that a try. Just make sure the plates open fully right at WOT and not before, because those modified shafts can twist really easily.
By the way, I can't wait to see your numbers when you get the chance to do more tests. I'm curious what your AFR's look like.
12-31-14, 05:37 AM
#54
carb whisperer
I think you've stumbled (no pun intended) on something important here, but you may be looking at it the wrong way. Perhaps it's not that the carb wants less fuel with boost, but less air. Allow me to throw out a theory:
We know there's always a pressure differential between the top of the carb (float bowls, air horn, etc) and the bottom (plenum under the throttle plates). That's how the thing works. It's what causes both air and fuel to flow through all these jets, bleeds, and circuits. I think boost multiplies this differential. While both sides are in fact pressurized, there's a greater difference in pressure between the air pushing into the carb and the air flowing through the manifold. The more restrictive the carburetor, the greater this effect will be. That's why stock-bore venturis may not work so well in boosted applications. Sound good so far?
So what may be going on here is an effect of this multiplied differential under boost. More pressure up top forces air through the air bleeds at a faster rate than at atmospheric pressures. It may have a similar effect on fuel, but air is far more easily moved than liquid. With the circuit full of air, there's a limit to how much fuel can be drawn into it, no matter what size the jet. This may be why when I changed my secondary fuel jets from 195 to a massive 238, I saw only a small decrease (richer) in AFR under boost. I figured 238 jets would just dump liquid fuel into the airstream and cause the engine to bog when I leaned on the throttle. I was shocked when this wasn't the case.
Getting back to this multiplied pressure differential - with your typical mechanical secondary setup, the effect is going to be strongest before the secondary plates just start to open. At this time, boost is beginning to build but the nearly closed secondary plates are causing a lot of restriction, causing pressure to rise on the top side much faster than in the manifold. This is happening right as the secondary slow air bleeds are doing their thing. The increased pressure up top forces a ton of air through the slow air bleeds, leaning the mixture considerably and causing your hesitation. When you soldered your slow air bleeds shut, you eliminated this. Reducing the size of the main secondary air bleeds also helped keep this high pressure differential from leaning out your mixture under boost, which is the problem I am having. So I guess I know what I need to do next!
So yeah, I think you pretty much nailed it when you said the carb needs less air bleed to accomplish the same thing under boost. Although if you don't drastically reduce the size of the secondary air bleeds, you may not even need to fool with the fuel jets.
And another note on the hiccup when you hit boost: One thing I did to my carb was modify the linkage a bit so the secondaries open sooner, with less throttle. This means my slow bleeds are doing their thing before the pressure rises, and the main fuel circuit kicks in before boost does. You may want to give that a try. Just make sure the plates open fully right at WOT and not before, because those modified shafts can twist really easily.
By the way, I can't wait to see your numbers when you get the chance to do more tests. I'm curious what your AFR's look like.
We know there's always a pressure differential between the top of the carb (float bowls, air horn, etc) and the bottom (plenum under the throttle plates). That's how the thing works. It's what causes both air and fuel to flow through all these jets, bleeds, and circuits. I think boost multiplies this differential. While both sides are in fact pressurized, there's a greater difference in pressure between the air pushing into the carb and the air flowing through the manifold. The more restrictive the carburetor, the greater this effect will be. That's why stock-bore venturis may not work so well in boosted applications. Sound good so far?
So what may be going on here is an effect of this multiplied differential under boost. More pressure up top forces air through the air bleeds at a faster rate than at atmospheric pressures. It may have a similar effect on fuel, but air is far more easily moved than liquid. With the circuit full of air, there's a limit to how much fuel can be drawn into it, no matter what size the jet. This may be why when I changed my secondary fuel jets from 195 to a massive 238, I saw only a small decrease (richer) in AFR under boost. I figured 238 jets would just dump liquid fuel into the airstream and cause the engine to bog when I leaned on the throttle. I was shocked when this wasn't the case.
Getting back to this multiplied pressure differential - with your typical mechanical secondary setup, the effect is going to be strongest before the secondary plates just start to open. At this time, boost is beginning to build but the nearly closed secondary plates are causing a lot of restriction, causing pressure to rise on the top side much faster than in the manifold. This is happening right as the secondary slow air bleeds are doing their thing. The increased pressure up top forces a ton of air through the slow air bleeds, leaning the mixture considerably and causing your hesitation. When you soldered your slow air bleeds shut, you eliminated this. Reducing the size of the main secondary air bleeds also helped keep this high pressure differential from leaning out your mixture under boost, which is the problem I am having. So I guess I know what I need to do next!
So yeah, I think you pretty much nailed it when you said the carb needs less air bleed to accomplish the same thing under boost. Although if you don't drastically reduce the size of the secondary air bleeds, you may not even need to fool with the fuel jets.
And another note on the hiccup when you hit boost: One thing I did to my carb was modify the linkage a bit so the secondaries open sooner, with less throttle. This means my slow bleeds are doing their thing before the pressure rises, and the main fuel circuit kicks in before boost does. You may want to give that a try. Just make sure the plates open fully right at WOT and not before, because those modified shafts can twist really easily.
By the way, I can't wait to see your numbers when you get the chance to do more tests. I'm curious what your AFR's look like.
I have a different theory. I think it has more to do with the speed and volume of air being forced through the carb.
Ultimately, carbs are metered to deliver fuel via booster signal. If the carb is small enough, and the boost high enough, the air speed moving over the booster will be very VERY high. The nikki has extremely responsive boosters. I think it is simply reacting to the massive influx of air and pushing the venturi effect a little harder than it would normally.
That 10 jet size is around 5-6% fuel flow, which isnt much honestly in terms of definition. Which, is in the realms of possibility with the above theory.
I wouldnt be shocked at all if you turned the boost off and suddenly the engine wanted larger secondary jets.
12-31-14, 02:43 PM
#55
LizardFC, I think your secondaries would work better if you filled the slow air bleeds with solder and test drove it. I bet the AFR will get richer like you're thinking. There shouldn't be any need for such massive secondary jets. I think bad83 needed to up his because he didn't fill the slow air bleeds with solder either. So fill them and see how it goes. Then make your sec main bleeds smaller (130 to 120 or there abouts) to fine tune the AFR like I did. Your secondary jets will probably end up being a lot smaller than they are now.
Remember the secondary slow air bleeds and even the main air bleeds were sized to work smoothly with vacuum secondaries. By going mechanical, all you need is to get rid of the delay/bog/hiccup and it seems reducing most of the air is the way to go. But reducing the air means you must also reduce the fuel, but by a smaller amount. So like 20 for air (or more like 60 or over 100 if you include the filled slow air bleeds), and only 10 for fuel. Well, I'm just rehashing stuff we already know so I'll move on now.
You mentioned thinned throttle shafts. I didn't do that mod because I don't believe in it. It seems only necessary for some 12As that are NA that need as many advantages as possible. With boost, it doesn't really matter anymore. A small restriction can be made up for with a tiny increase in boost so I'm not worried about leaving a little HP on the table. Sure a thinned throttle shaft would help my 13B as well, but I don't want run the risk of twisting a shaft. Plus it's hard to get it just right and you can damage the brass butterflies or lose a screw into the engine. So no thinned thottle shafts for me. My setup is already almost too powerful as it is with no intercooler and only the factory wastegate spring setting of like 7psi or whatever the S5 has. It's just the beginning for me.
You also mentioned enlarged primary venturis as actually beneficial for boost. You may be on to something. I obviously needed enlarged venturis because the 13B will flow a certan percent more at the exact same RPM as a 12A does. So it threw the idle circuit out of its range a bit, but I corrected it by swapping out the stock brass 170 slow air bleeds and throwing in nickel plated 60s that I drilled out with my 118 drill bit. The drill bit is about the same size as about a factory 122 to 123 (if such a size existed). Either way I went from 170 which didn't work at all after the enalrged venturis went in and the primary jet was reduced from 130 to a drilled 118 for the turbo tune, to a set of brass 150s out of an SA carb, which was slightly better but still unuseable, but it let me know I was headed in the right direction. Then because I had the 118 drill bit (.045"), I went for it on a spare set of nickel plated 60s. Swapped them in and got a Perfect idle!
So as you see, the primary side also benefits from reduced air bleeds. Not even bad83 did this mod. I think it's because his carb didn't need it to keep his 12A idling correctly. He did state that you need to leave the primary stuff alone and only up the secondary fuel jets. I believe only Sterling ever experimented with the nickel plated 60s, and that was only on carbs that didn't want to idle. I suspect it could have been any number of issues like a brass butterfly not seated perfectly true after his thinned throttle shaft work, or maybe it was just the enlarged venturis causing it, like on my carbs. Either way he said the nickel plated 60s make the idle SUPER rich. I was a bit worried about that, so I decided to drill a spare set with the 118 drill bit to see what would happen and viola! Perfect idle. It made the mixture screw actually work again instead of doing nothing or very nearly nothing no matter how far turned in or out it was. Hence it brought the idle circuit back into "calibration" as I've mentioned before.
As for your 238 jets, I have a set someone drilled out with a standard drill bit which is more or less the same as one I have here, which I poked into it to see how close it was. When measured with a digital caliper, it came in at around 235. It's essentially the same size as yours. Man that would be way too big for my setup.
wankel=awesome, you may be right about the efficient boosters working "better" or stronger with the greater amount of air flowing through them under boost. It's very possible.
The carb certainly wants richer primary jets when the turbo is removed. So that much is true. I suspect the secondaries are going to be the same (I just need more driving time to test this). At first I thought the increased air flow through an RB spun aluminum air cleaner assembly, which is less restricitive than a carb hat and a charge pipe, having to breath through a compressor wheel when the turbo is spinning slow at low RPM, was the reason. Then there is a giant cork in the exhaust side consisting of the exhaust manifold and having to flow though the turbine wheel and fairly restrictive exhaust housing and dumped into a 3" down pipe which might have a bit of an air slug problem at low RPM. Compare that with a nice free flowing long primary exhaust like the RB or any other well designed NA exhaust. I can tell you this much: the NA setup in this car does rev freer and faster than when the cork is installed. The NA setup is actually quite enjoyable to drive and rewarding by itself. It is, in my opinion, the right amount of power for this chassis and, in my opinion, they should have came like this from the factory. Major improvement over a stock or nearly stock GSL-SE setup like my brother had, or a recent S4 NA complete swap into PercentSevenC's red '84 GSL, which is only mildly more powerful than my bro's stock GSL-SE. They are both way slow though compared with boost and still slower and less rewarding than my 4 port R5 13B NA setup with a hogged out Nikki. But what about the 12A that started it all in the SA? No thanks. 30 pound flywheel? In car that size? Never. I don't think they could even keep up with most of today's traffic, what with grocery getters getting like 200HP Now. You almost need at least a stock GSL-SE to keep up with them.
So I'll let you guys discuss the more deep carb theory stuff. It makes my head hurt. Heck it took me like 8 months of off and on carb testing to get the boost prepped Nikki to work right on my setup. I would have gotten it done sooner if I had more basic carb knowledge I suppose, and there were times, like with tg_farrel where we struggled for a while and wanted to give up until some sentence on the forum caught or eye, or someone stepped up with an idea, or we came up with it ourselves. Or like when I finally sat myself down and read all the way through that one website about boost prepping a Holley where the idea to fill the secondary slow air bleeds with solder finally clicked. Yes, Holley doesn't = Nikki, but the theory was sound, so I went for it. And it worked! No more 1.5 to 2 second delay every time I wanted to boost it. It dropped to about 1/4 second to no more than 1/2 second. Then the smaller secondary main air bleeds got rid of the last of the delay so now it's either completely gone or so short I don't notice it anymore. Hey, from my perspective, that's good enough! Time to share the info, and here I am.
Remember the secondary slow air bleeds and even the main air bleeds were sized to work smoothly with vacuum secondaries. By going mechanical, all you need is to get rid of the delay/bog/hiccup and it seems reducing most of the air is the way to go. But reducing the air means you must also reduce the fuel, but by a smaller amount. So like 20 for air (or more like 60 or over 100 if you include the filled slow air bleeds), and only 10 for fuel. Well, I'm just rehashing stuff we already know so I'll move on now.
You mentioned thinned throttle shafts. I didn't do that mod because I don't believe in it. It seems only necessary for some 12As that are NA that need as many advantages as possible. With boost, it doesn't really matter anymore. A small restriction can be made up for with a tiny increase in boost so I'm not worried about leaving a little HP on the table. Sure a thinned throttle shaft would help my 13B as well, but I don't want run the risk of twisting a shaft. Plus it's hard to get it just right and you can damage the brass butterflies or lose a screw into the engine. So no thinned thottle shafts for me. My setup is already almost too powerful as it is with no intercooler and only the factory wastegate spring setting of like 7psi or whatever the S5 has. It's just the beginning for me.
You also mentioned enlarged primary venturis as actually beneficial for boost. You may be on to something. I obviously needed enlarged venturis because the 13B will flow a certan percent more at the exact same RPM as a 12A does. So it threw the idle circuit out of its range a bit, but I corrected it by swapping out the stock brass 170 slow air bleeds and throwing in nickel plated 60s that I drilled out with my 118 drill bit. The drill bit is about the same size as about a factory 122 to 123 (if such a size existed). Either way I went from 170 which didn't work at all after the enalrged venturis went in and the primary jet was reduced from 130 to a drilled 118 for the turbo tune, to a set of brass 150s out of an SA carb, which was slightly better but still unuseable, but it let me know I was headed in the right direction. Then because I had the 118 drill bit (.045"), I went for it on a spare set of nickel plated 60s. Swapped them in and got a Perfect idle!
So as you see, the primary side also benefits from reduced air bleeds.
Not even bad83 did this mod. I think it's because his carb didn't need it to keep his 12A idling correctly. He did state that you need to leave the primary stuff alone and only up the secondary fuel jets. I believe only Sterling ever experimented with the nickel plated 60s, and that was only on carbs that didn't want to idle. I suspect it could have been any number of issues like a brass butterfly not seated perfectly true after his thinned throttle shaft work, or maybe it was just the enlarged venturis causing it, like on my carbs. Either way he said the nickel plated 60s make the idle SUPER rich. I was a bit worried about that, so I decided to drill a spare set with the 118 drill bit to see what would happen and viola! Perfect idle. It made the mixture screw actually work again instead of doing nothing or very nearly nothing no matter how far turned in or out it was. Hence it brought the idle circuit back into "calibration" as I've mentioned before.As for your 238 jets, I have a set someone drilled out with a standard drill bit which is more or less the same as one I have here, which I poked into it to see how close it was. When measured with a digital caliper, it came in at around 235. It's essentially the same size as yours. Man that would be way too big for my setup.
wankel=awesome, you may be right about the efficient boosters working "better" or stronger with the greater amount of air flowing through them under boost. It's very possible.
The carb certainly wants richer primary jets when the turbo is removed. So that much is true. I suspect the secondaries are going to be the same (I just need more driving time to test this). At first I thought the increased air flow through an RB spun aluminum air cleaner assembly, which is less restricitive than a carb hat and a charge pipe, having to breath through a compressor wheel when the turbo is spinning slow at low RPM, was the reason. Then there is a giant cork in the exhaust side consisting of the exhaust manifold and having to flow though the turbine wheel and fairly restrictive exhaust housing and dumped into a 3" down pipe which might have a bit of an air slug problem at low RPM. Compare that with a nice free flowing long primary exhaust like the RB or any other well designed NA exhaust. I can tell you this much: the NA setup in this car does rev freer and faster than when the cork is installed. The NA setup is actually quite enjoyable to drive and rewarding by itself. It is, in my opinion, the right amount of power for this chassis and, in my opinion, they should have came like this from the factory. Major improvement over a stock or nearly stock GSL-SE setup like my brother had, or a recent S4 NA complete swap into PercentSevenC's red '84 GSL, which is only mildly more powerful than my bro's stock GSL-SE. They are both way slow though compared with boost and still slower and less rewarding than my 4 port R5 13B NA setup with a hogged out Nikki.
But what about the 12A that started it all in the SA? No thanks. 30 pound flywheel? In car that size? Never. I don't think they could even keep up with most of today's traffic, what with grocery getters getting like 200HP Now. You almost need at least a stock GSL-SE to keep up with them.So I'll let you guys discuss the more deep carb theory stuff. It makes my head hurt. Heck it took me like 8 months of off and on carb testing to get the boost prepped Nikki to work right on my setup. I would have gotten it done sooner if I had more basic carb knowledge I suppose, and there were times, like with tg_farrel where we struggled for a while and wanted to give up until some sentence on the forum caught or eye, or someone stepped up with an idea, or we came up with it ourselves. Or like when I finally sat myself down and read all the way through that one website about boost prepping a Holley where the idea to fill the secondary slow air bleeds with solder finally clicked. Yes, Holley doesn't = Nikki, but the theory was sound, so I went for it. And it worked! No more 1.5 to 2 second delay every time I wanted to boost it. It dropped to about 1/4 second to no more than 1/2 second. Then the smaller secondary main air bleeds got rid of the last of the delay so now it's either completely gone or so short I don't notice it anymore. Hey, from my perspective, that's good enough! Time to share the info, and here I am.
01-01-15, 11:37 PM
#56
I have a different theory. I think it has more to do with the speed and volume of air being forced through the carb.
Ultimately, carbs are metered to deliver fuel via booster signal. If the carb is small enough, and the boost high enough, the air speed moving over the booster will be very VERY high. The nikki has extremely responsive boosters. I think it is simply reacting to the massive influx of air and pushing the venturi effect a little harder than it would normally.
That 10 jet size is around 5-6% fuel flow, which isnt much honestly in terms of definition. Which, is in the realms of possibility with the above theory.
I wouldnt be shocked at all if you turned the boost off and suddenly the engine wanted larger secondary jets.
Ultimately, carbs are metered to deliver fuel via booster signal. If the carb is small enough, and the boost high enough, the air speed moving over the booster will be very VERY high. The nikki has extremely responsive boosters. I think it is simply reacting to the massive influx of air and pushing the venturi effect a little harder than it would normally.
That 10 jet size is around 5-6% fuel flow, which isnt much honestly in terms of definition. Which, is in the realms of possibility with the above theory.
I wouldnt be shocked at all if you turned the boost off and suddenly the engine wanted larger secondary jets.
Also, I don't believe boost pressure has any positive effect on air velocity in the venturis. Air velocity through the intake system is ultimately determined by engine speed. The engine will only handle so much volume at a given RPM. When the volumetric limit is reached, the air begins to compress. It's essentially stuck in traffic. It can't move any faster, so it becomes denser. Denser air also means more friction, which can reduce air velocity a bit.
If the rain holds off this weekend I'm going to do some experimenting. That's not looking likely though. I'll try plugging the slow air bleeds first. I have a couple of spare carbs I can grab stock parts from if it doesn't work.
01-02-15, 08:52 AM
#57
carb whisperer
That was what I thought initially, and why I was surprised when my drastic changes to the fuel jets didn't give me proportional results. I started off with 185's, which caused my AFR to shoot into the 14's and stumble under boost. Good thing I'm running really conservative timing. I drilled the jets out to 205. AFR's settled into the mid 13's under boost. Next I went for broke with a 3/32 bit which comes out to about 238. Mind you that's nearly 1.5 times the size of the factory jet. A stronger signal with this size jet should flood the carb when the secondaries open. But it still runs in the low 13's. So that's why I think more is going on here.
Also, I don't believe boost pressure has any positive effect on air velocity in the venturis. Air velocity through the intake system is ultimately determined by engine speed. The engine will only handle so much volume at a given RPM. When the volumetric limit is reached, the air begins to compress. It's essentially stuck in traffic. It can't move any faster, so it becomes denser. Denser air also means more friction, which can reduce air velocity a bit.
If the rain holds off this weekend I'm going to do some experimenting. That's not looking likely though. I'll try plugging the slow air bleeds first. I have a couple of spare carbs I can grab stock parts from if it doesn't work.
Also, I don't believe boost pressure has any positive effect on air velocity in the venturis. Air velocity through the intake system is ultimately determined by engine speed. The engine will only handle so much volume at a given RPM. When the volumetric limit is reached, the air begins to compress. It's essentially stuck in traffic. It can't move any faster, so it becomes denser. Denser air also means more friction, which can reduce air velocity a bit.
If the rain holds off this weekend I'm going to do some experimenting. That's not looking likely though. I'll try plugging the slow air bleeds first. I have a couple of spare carbs I can grab stock parts from if it doesn't work.
Intake manifold design and porting could also be playing a major role in your differences. 13 AFR is a little lean for my tastes, at WOT 7k+ rpm's. My 12a generates so much signal with a holley at those RPM's that a 58 fuel jet provides more than enough fuel up top to support 13:1, yet its only enough to do 14:1 AT 5K RPM's.
Figuring in the actual fuel needed to keep the fire lit as the rpm's rise, one can see that it is NOT linear signal. It gets extremely high as the engine picks up speed, and in my case can pull a ton more fuel through a smaller jet than I thought possible before triple emulsions.
Jeff20b's experimentation with his emulsion tubes (and ignition system) could very well be whats changing his curve so drastically from yours.
The real test, would be a WOT consumption test. The measurement on just how much gasoline your build requires for 30 seconds in gear from 5-7k rpm, and his.
I would wager that despite the radical differences in jetting, that they would come out very close in value.
At the end of the day, X air will need Y fuel to support itself at a given and set AFR, in terms of demand.
01-02-15, 09:27 PM
#58
Right, but the air moving through the engine before the "traffic" should be at least the 10% hes seeing. That engine isnt limited so early in airflow as the modded nikki permits. I wouldnt sit here and theorize that you could pick up 50% fuel flow from forcing air through a carb, but 10% is totally possible.
Intake manifold design and porting could also be playing a major role in your differences. 13 AFR is a little lean for my tastes, at WOT 7k+ rpm's. My 12a generates so much signal with a holley at those RPM's that a 58 fuel jet provides more than enough fuel up top to support 13:1, yet its only enough to do 14:1 AT 5K RPM's.
Figuring in the actual fuel needed to keep the fire lit as the rpm's rise, one can see that it is NOT linear signal. It gets extremely high as the engine picks up speed, and in my case can pull a ton more fuel through a smaller jet than I thought possible before triple emulsions.
Jeff20b's experimentation with his emulsion tubes (and ignition system) could very well be whats changing his curve so drastically from yours.
The real test, would be a WOT consumption test. The measurement on just how much gasoline your build requires for 30 seconds in gear from 5-7k rpm, and his.
I would wager that despite the radical differences in jetting, that they would come out very close in value.
At the end of the day, X air will need Y fuel to support itself at a given and set AFR, in terms of demand.
Intake manifold design and porting could also be playing a major role in your differences. 13 AFR is a little lean for my tastes, at WOT 7k+ rpm's. My 12a generates so much signal with a holley at those RPM's that a 58 fuel jet provides more than enough fuel up top to support 13:1, yet its only enough to do 14:1 AT 5K RPM's.
Figuring in the actual fuel needed to keep the fire lit as the rpm's rise, one can see that it is NOT linear signal. It gets extremely high as the engine picks up speed, and in my case can pull a ton more fuel through a smaller jet than I thought possible before triple emulsions.
Jeff20b's experimentation with his emulsion tubes (and ignition system) could very well be whats changing his curve so drastically from yours.
The real test, would be a WOT consumption test. The measurement on just how much gasoline your build requires for 30 seconds in gear from 5-7k rpm, and his.
I would wager that despite the radical differences in jetting, that they would come out very close in value.
At the end of the day, X air will need Y fuel to support itself at a given and set AFR, in terms of demand.
I haven't been able to try WOT yet on mine. I get to about 80% throttle and see the AFR's go into the 13's so I lift. Maybe this weekend if the air bleed experiment works out I'll get to. I can't wait to see what this thing will do when I get the mixture right and can start advancing the timing and raising the boost a bit. I'd like to get it on the dyno before I blow it up.
01-03-15, 02:39 AM
#59
You changed your secondary linkage/opening timing. Could that have something to do with anything? I left mine stock and it seems to work perfectly. My mecanical secondaries were welded, not wired or tied or linkage flipped. Welded for strength and security under boost.
01-03-15, 08:34 PM
#60
I just wired mine. I can adjust how early they open by tightening and loosening the wire. It's held up for at least 5 years now so I'm not too worried about that.
Today I tried closing the secondary slow air bleeds. I used jbweld. The experiment was a failure, but for unforeseen reasons. Somewhere between the driveway and the garage, the fuel pump died! I had plenty of fuel pressure when I pulled it in there. I started it up, backed it out, and it ran for a bit and died. No fuel pressure, and an unfamiliar silence from behind the driver's seat. Walbro pumps are kind enough to let you know when they're working. So no test runs today. I'm going to test the wiring and relay tomorrow and if it checks out, I'll be ordering a different pump. This one only has maybe 500 miles on it!
Today I tried closing the secondary slow air bleeds. I used jbweld. The experiment was a failure, but for unforeseen reasons. Somewhere between the driveway and the garage, the fuel pump died! I had plenty of fuel pressure when I pulled it in there. I started it up, backed it out, and it ran for a bit and died. No fuel pressure, and an unfamiliar silence from behind the driver's seat. Walbro pumps are kind enough to let you know when they're working. So no test runs today. I'm going to test the wiring and relay tomorrow and if it checks out, I'll be ordering a different pump. This one only has maybe 500 miles on it!
01-04-15, 01:16 AM
#61
I remember you were having all kinds of trouble with your Walbro. Maybe it's the reason your carb has been hard to tune (running lean at high RPM even with massive secondary jets). It's about time to get an MSD pump. If it's good enough for my 13B...
If it's good enough for my 13B...
01-04-15, 01:27 AM
#62
I prepped four more sec air bleeds to accept fuel jets. I accidentally drilled one slightly too deep which caused the emulsion tube to fall off. It didn't come off until the threads were getting cut. Oops. 
So don't drill them too deep.
I have one spare modified air bleed now I suppose.
I guess if some other carb needs one, I'm good.
So don't drill them too deep.I have one spare modified air bleed now I suppose.
I guess if some other carb needs one, I'm good.
01-04-15, 10:23 PM
#64
Turns out the Walbro was okay, I just blew the fuse under the dash. Not sure how, since it was a 30a fuse and I'm running a separate relay, but whatever. I got it out for a test run today. It didn't go so well. It was rich under boost, but sporadically so. No power like before, AFR's were all over the place. 10's, 11's, 13's... I couldn't get a steady number and I could feel power responding the same. After a run at boost, I had a hard time keeping the car running. Idle was high, lumpy, and it shut off a few times coming to a stop. AFR's were all over the place. It was a struggle to get it home. So plugging up the secondary slow air bleeds wasn't good for this carb.
Next plan of action, I'm going to give the plugged slow air bleeds another shot but with stock 160 secondary fuel jets. It's possible that my oversized fuel jets were making it rain liquid fuel and preventing the mixture from being atomized. I may have ended up with a manifold full of raw fuel. So I'll try and eliminate that possibility.
If that doesn't work, then it's back to stock with the slow air bleeds. I'll try modifying my secondary main air bleeds like you have so I can step those down. That would make tuning much easier, since I could buy a range of holley jets to play with.
Next plan of action, I'm going to give the plugged slow air bleeds another shot but with stock 160 secondary fuel jets. It's possible that my oversized fuel jets were making it rain liquid fuel and preventing the mixture from being atomized. I may have ended up with a manifold full of raw fuel. So I'll try and eliminate that possibility.
If that doesn't work, then it's back to stock with the slow air bleeds. I'll try modifying my secondary main air bleeds like you have so I can step those down. That would make tuning much easier, since I could buy a range of holley jets to play with.
01-06-15, 09:41 PM
#65
It's possible a swap back to 160s will help, but pay close attention to your AFRs.
Rome was not built in a day, and neither is a turbo tune. It took me months with lots of confusion and setbacks. Then whenever a mod I did actually worked as expected, it was cause to celebrate. So be sure to celebrate when you have a breakthough and we'll pat you on the back in a non physical internet kind of way.
Rome was not built in a day, and neither is a turbo tune. It took me months with lots of confusion and setbacks. Then whenever a mod I did actually worked as expected, it was cause to celebrate. So be sure to celebrate when you have a breakthough and we'll pat you on the back in a non physical internet kind of way.
01-12-15, 10:50 PM
#66
I semi-locked three distributors today.
What you do is strip the dizzy down enough to take out the upper shaft. It looks like an upside down T. There are two slots. You only need to fill one of them partially with weld. Grind to clean it up. Assemble in reverse order.
You're like c'mon, you can spill more than that. Ok, I will say this. The slot is about 10mm long (9.9mm but we'll call it 10). The slider pin is about 5mm diameter. It moves 5mm during mechanical advance. This translates to 10 degrees of dizzy dvance which translates to 20 degrees of eccentric shaft advance, or rather 20 degrees of mechanical advance as seen with a timing light. Easy, right?
So then how do you so called "semi-lock" it? What is your definition? What are you talking about?
It is modified from the root term "locked distributor" where you simply weld the slider pins in the slot and then time your dizzy for 10 degrees. It stays at 10 degrees all the time. This kinda screws with your idle quality and I knew there was a better way, so when I acquired a modified dizzy that only could advance 10 degrees but wasn't actually locked, I started calling it semi-locked and the term stuck. I've since tested this dizzy for 200 miles on a boosted setup and it works great. Good idle quality and no detonation in boost.
So I dissassembled it along with three other stock dizzies today to see if I could mimic the work the PO did. I think I did a decent job. I grabbed a spare shaft just in case, but ended up doing fine. So now I have four modded shafts. I made sure to label each one so it went back in its oiriginal dizzy. Turns out the N249 has a longer slot with the number 14 (or 114) stamped. The N231 and N201 are the same with the number 115 stamped. j9fd3s probably knows what I'm talking about.
You just add metal until the slot is shortened by 2.5mm. Then clean up with a grinder, a dremel and a hand file just shy of 5mm to do final shaping. The end result should let the pin slide easily in the slot without getting stuck on anything. Then grease and install. It couldn't be any simpler. I found the more dizzies, I worked on, the easier they got. I could probabyl strip one down, grease it and throw it back together in a few minutes.
Anyway I'm rambling now. In closing I'll just say a boosted Nikki needs a semi-locked dizzy. Forget fully locked. Those are about as exciting as yesterday's news.
What you do is strip the dizzy down enough to take out the upper shaft. It looks like an upside down T. There are two slots. You only need to fill one of them partially with weld. Grind to clean it up. Assemble in reverse order.
You're like c'mon, you can spill more than that. Ok, I will say this. The slot is about 10mm long (9.9mm but we'll call it 10). The slider pin is about 5mm diameter. It moves 5mm during mechanical advance. This translates to 10 degrees of dizzy dvance which translates to 20 degrees of eccentric shaft advance, or rather 20 degrees of mechanical advance as seen with a timing light. Easy, right?
So then how do you so called "semi-lock" it? What is your definition? What are you talking about?
It is modified from the root term "locked distributor" where you simply weld the slider pins in the slot and then time your dizzy for 10 degrees. It stays at 10 degrees all the time. This kinda screws with your idle quality and I knew there was a better way, so when I acquired a modified dizzy that only could advance 10 degrees but wasn't actually locked, I started calling it semi-locked and the term stuck. I've since tested this dizzy for 200 miles on a boosted setup and it works great. Good idle quality and no detonation in boost.
So I dissassembled it along with three other stock dizzies today to see if I could mimic the work the PO did. I think I did a decent job. I grabbed a spare shaft just in case, but ended up doing fine. So now I have four modded shafts. I made sure to label each one so it went back in its oiriginal dizzy. Turns out the N249 has a longer slot with the number 14 (or 114) stamped. The N231 and N201 are the same with the number 115 stamped. j9fd3s probably knows what I'm talking about.
You just add metal until the slot is shortened by 2.5mm. Then clean up with a grinder, a dremel and a hand file just shy of 5mm to do final shaping. The end result should let the pin slide easily in the slot without getting stuck on anything. Then grease and install. It couldn't be any simpler. I found the more dizzies, I worked on, the easier they got. I could probabyl strip one down, grease it and throw it back together in a few minutes.
Anyway I'm rambling now. In closing I'll just say a boosted Nikki needs a semi-locked dizzy. Forget fully locked. Those are about as exciting as yesterday's news.
01-13-15, 07:11 PM
#67
I semi-locked three distributors today.
What you do is strip the dizzy down enough to take out the upper shaft. It looks like an upside down T. There are two slots. You only need to fill one of them partially with weld. Grind to clean it up. Assemble in reverse order.
You're like c'mon, you can spill more than that. Ok, I will say this. The slot is about 10mm long (9.9mm but we'll call it 10). The slider pin is about 5mm diameter. It moves 5mm during mechanical advance. This translates to 10 degrees of dizzy dvance which translates to 20 degrees of eccentric shaft advance, or rather 20 degrees of mechanical advance as seen with a timing light. Easy, right?
So then how do you so called "semi-lock" it? What is your definition? What are you talking about?
It is modified from the root term "locked distributor" where you simply weld the slider pins in the slot and then time your dizzy for 10 degrees. It stays at 10 degrees all the time. This kinda screws with your idle quality and I knew there was a better way, so when I acquired a modified dizzy that only could advance 10 degrees but wasn't actually locked, I started calling it semi-locked and the term stuck. I've since tested this dizzy for 200 miles on a boosted setup and it works great. Good idle quality and no detonation in boost.
So I dissassembled it along with three other stock dizzies today to see if I could mimic the work the PO did. I think I did a decent job. I grabbed a spare shaft just in case, but ended up doing fine. So now I have four modded shafts. I made sure to label each one so it went back in its oiriginal dizzy. Turns out the N249 has a longer slot with the number 14 (or 114) stamped. The N231 and N201 are the same with the number 115 stamped. j9fd3s probably knows what I'm talking about.
You just add metal until the slot is shortened by 2.5mm. Then clean up with a grinder, a dremel and a hand file just shy of 5mm to do final shaping. The end result should let the pin slide easily in the slot without getting stuck on anything. Then grease and install. It couldn't be any simpler. I found the more dizzies, I worked on, the easier they got. I could probabyl strip one down, grease it and throw it back together in a few minutes.
Anyway I'm rambling now. In closing I'll just say a boosted Nikki needs a semi-locked dizzy. Forget fully locked. Those are about as exciting as yesterday's news.
What you do is strip the dizzy down enough to take out the upper shaft. It looks like an upside down T. There are two slots. You only need to fill one of them partially with weld. Grind to clean it up. Assemble in reverse order.
You're like c'mon, you can spill more than that. Ok, I will say this. The slot is about 10mm long (9.9mm but we'll call it 10). The slider pin is about 5mm diameter. It moves 5mm during mechanical advance. This translates to 10 degrees of dizzy dvance which translates to 20 degrees of eccentric shaft advance, or rather 20 degrees of mechanical advance as seen with a timing light. Easy, right?
So then how do you so called "semi-lock" it? What is your definition? What are you talking about?
It is modified from the root term "locked distributor" where you simply weld the slider pins in the slot and then time your dizzy for 10 degrees. It stays at 10 degrees all the time. This kinda screws with your idle quality and I knew there was a better way, so when I acquired a modified dizzy that only could advance 10 degrees but wasn't actually locked, I started calling it semi-locked and the term stuck. I've since tested this dizzy for 200 miles on a boosted setup and it works great. Good idle quality and no detonation in boost.
So I dissassembled it along with three other stock dizzies today to see if I could mimic the work the PO did. I think I did a decent job. I grabbed a spare shaft just in case, but ended up doing fine. So now I have four modded shafts. I made sure to label each one so it went back in its oiriginal dizzy. Turns out the N249 has a longer slot with the number 14 (or 114) stamped. The N231 and N201 are the same with the number 115 stamped. j9fd3s probably knows what I'm talking about.
You just add metal until the slot is shortened by 2.5mm. Then clean up with a grinder, a dremel and a hand file just shy of 5mm to do final shaping. The end result should let the pin slide easily in the slot without getting stuck on anything. Then grease and install. It couldn't be any simpler. I found the more dizzies, I worked on, the easier they got. I could probabyl strip one down, grease it and throw it back together in a few minutes.
Anyway I'm rambling now. In closing I'll just say a boosted Nikki needs a semi-locked dizzy. Forget fully locked. Those are about as exciting as yesterday's news.
I tried welding the first dizzy I took apart and all went well until I put it back together. There were tiny bits of slag on the shaft that kept it from spinning smooth. Some of them got down where I couldn't grind or chip them off. So I tossed that one and just unlocked my spare. Lesson learned: If you're going to weld the weights in place, cover the shaft in tape or something so no metal splatters on it.
I haven't had a chance to play with my carb anymore, btw. Hoping for decent weather this weekend.
01-14-15, 01:28 AM
#68
Originally Posted by LizardFC
I call mine "unlocked" because I didn't weld it, I just took the springs out so it flops to full advance when the engine turns. Your idea is intriguing. I didn't think about putting a physical stop on the slots themselves. I'd worry a little about it throwing the balance off if you added a lot of metal. Do you have your vacuum advance hooked up?
I tried welding the first dizzy I took apart and all went well until I put it back together. There were tiny bits of slag on the shaft that kept it from spinning smooth. Some of them got down where I couldn't grind or chip them off. So I tossed that one and just unlocked my spare. Lesson learned: If you're going to weld the weights in place, cover the shaft in tape or something so no metal splatters on it.
I haven't had a chance to play with my carb anymore, btw. Hoping for decent weather this weekend.
I tried welding the first dizzy I took apart and all went well until I put it back together. There were tiny bits of slag on the shaft that kept it from spinning smooth. Some of them got down where I couldn't grind or chip them off. So I tossed that one and just unlocked my spare. Lesson learned: If you're going to weld the weights in place, cover the shaft in tape or something so no metal splatters on it.
I haven't had a chance to play with my carb anymore, btw. Hoping for decent weather this weekend.
I welded (fully locked) a dizzy once. To avoid what happened to you, I punched out the roll pin at the bottom, took off the drive gear, pulled the entire shaft and had easier access to weld the weights. I don't recall what I covered the shaft with, but it must have been good enough because it all went back in fine.
I worried about throwing the balance off too, but the PO didn't worry about it, and the dizzy worked fine, so I didn't worry about it either.
No vacuum advance here. I think it would cause more trouble than it would solve. I once tried it on a Camden and it made things kinda weird so I disconnected it. The problem is you need a timed vacuum source. Maybe I didn't realize this back then. Do you have any reasons to use vacuum advance? Lay it on me, bro.
01-15-15, 01:01 AM
#69
So now I'm up to six semi-locked Dizzies. On this one, I decided to do a little more advance. I did some calculations and came up with 15 degrees of advance. So I cut the slot accordingly. Now that it's back together, it looks like it worked out, from a static timing perspective that is (just eyeballing it).
Once you get the hang of working with these, they're actually kinda nice to work on, as are the Nikkis themselves. No need for an ECU and all that expensive EFI jazz if you're competent.
Once you get the hang of working with these, they're actually kinda nice to work on, as are the Nikkis themselves. No need for an ECU and all that expensive EFI jazz if you're competent.
01-15-15, 05:21 PM
#70
Um, if it flops to full advance when the engine turns, does it go back when the engine doesn't turn? What good does this "mod" do? Sounds like a bad idea to me. The only good thing about it is it's reversible.
I welded (fully locked) a dizzy once. To avoid what happened to you, I punched out the roll pin at the bottom, took off the drive gear, pulled the entire shaft and had easier access to weld the weights. I don't recall what I covered the shaft with, but it must have been good enough because it all went back in fine.
I worried about throwing the balance off too, but the PO didn't worry about it, and the dizzy worked fine, so I didn't worry about it either.
No vacuum advance here. I think it would cause more trouble than it would solve. I once tried it on a Camden and it made things kinda weird so I disconnected it. The problem is you need a timed vacuum source. Maybe I didn't realize this back then. Do you have any reasons to use vacuum advance? Lay it on me, bro.
I welded (fully locked) a dizzy once. To avoid what happened to you, I punched out the roll pin at the bottom, took off the drive gear, pulled the entire shaft and had easier access to weld the weights. I don't recall what I covered the shaft with, but it must have been good enough because it all went back in fine.
I worried about throwing the balance off too, but the PO didn't worry about it, and the dizzy worked fine, so I didn't worry about it either.
No vacuum advance here. I think it would cause more trouble than it would solve. I once tried it on a Camden and it made things kinda weird so I disconnected it. The problem is you need a timed vacuum source. Maybe I didn't realize this back then. Do you have any reasons to use vacuum advance? Lay it on me, bro.
The vacuum advance is just supposed to help low RPM, low throttle drivability and mileage. It does nothing when under boost, since there's no vacuum. So with a supercharger it shouldn't really have an effect at all.
01-15-15, 10:15 PM
#72
Ah, I gotcha. Have you seen this thread yet? https://www.rx7club.com/1st-generati...boost-1077251/
I found this earlier while perusing RB's site: http://www.racingbeat.com/manuals/timingchart.pdf
There's a little note in there about recommended timing for boost. I can only assume they've done a ton of R&D on this. I wonder what their reasoning is behind leaving no split between leading and trailing?
01-15-15, 11:31 PM
#73
The no split thing is for p-ports. And it's a general guidline. I'm sure j9fd3s might have something to say about it.
As for their turbo timing recomendation, yeah 10 to 12 degrees of total advance sounds about right. They don't say anything about split though. I've recently read on the forum that some people recommend less than 8 to 10 degrees of split for a blow through turbo. I'm sticking with 10 degrees because it works for me.
I do have a dizzy with a trailing vacuum diaphram with really long slots. I can get it to zero split. It might be worth while to experiment with it.
As for their turbo timing recomendation, yeah 10 to 12 degrees of total advance sounds about right. They don't say anything about split though. I've recently read on the forum that some people recommend less than 8 to 10 degrees of split for a blow through turbo. I'm sticking with 10 degrees because it works for me.
I do have a dizzy with a trailing vacuum diaphram with really long slots. I can get it to zero split. It might be worth while to experiment with it.
01-16-15, 12:20 AM
#74
The no split thing is for p-ports. And it's a general guidline. I'm sure j9fd3s might have something to say about it.
As for their turbo timing recomendation, yeah 10 to 12 degrees of total advance sounds about right. They don't say anything about split though. I've recently read on the forum that some people recommend less than 8 to 10 degrees of split for a blow through turbo. I'm sticking with 10 degrees because it works for me.
I do have a dizzy with a trailing vacuum diaphram with really long slots. I can get it to zero split. It might be worth while to experiment with it.
As for their turbo timing recomendation, yeah 10 to 12 degrees of total advance sounds about right. They don't say anything about split though. I've recently read on the forum that some people recommend less than 8 to 10 degrees of split for a blow through turbo. I'm sticking with 10 degrees because it works for me.
I do have a dizzy with a trailing vacuum diaphram with really long slots. I can get it to zero split. It might be worth while to experiment with it.
capable of 300+ horsepower, we recommend both Leading
and Trailing timing be set at 10 to 12 degrees total advance,
at 6000 rpm, regardless of the porting configuration.
It says regardless of porting. I kinda want to try it too, when I get to that point. I don't think my stock port 12a will be capable of 300+ HP
At least I hope not or I'll have to switch transmissions. I'd be happy if it made 200RWHP. That would more than double the factory spec at the wheels with some carb mods and a few FC parts.
01-16-15, 01:25 PM
#75
Yeah, just aim for 200HP. It's double stock HP like you said. It's fun, practical, it won't break anything if you don't do anything stupid, and it will or should be able to break the tires loose just about any time.
Traction might be your number 1 concern, especially in colder weather. If you get stickier tires there is some danger to the diff and/or axles, or the clutch might slip. Something's gotta give. I'd rather it be the tires.
Whatever you do, don't mod your car too much like DirectFreak because it gets way too expensive and you're left with a car you don't want to drive anymore.
So don't chase the unicorn horn of 400HP or whatever. See how 200HP treats you, and if it's still not enough, make 250 or 300 your goal, but know it's a slippery slope.
I'm only planning on no more than 270HP because that's double the stock GSL-SE's 135HP, but I might not get there because I'm having way too much fun at stock S5 wastegate spring pressure of 7psi or so. Actually just today I read something in the FC section where a guy stated the S4 and S5 are both at 5.5psi and the S5 has some sort of boost solenoid controlled by the ECU which gets it closer to 9psi. That's the first time I've ever seen that info, so no way to know whether it's true. Heck maybe my setup with a stock wastegate size, which is known to be small, and a full 3" exhaust, is experiencing boost creep.
Here's a link. https://www.rx7club.com/2nd-generati.../#post11856428
Traction might be your number 1 concern, especially in colder weather.
If you get stickier tires there is some danger to the diff and/or axles, or the clutch might slip. Something's gotta give. I'd rather it be the tires. Whatever you do, don't mod your car too much like DirectFreak because it gets way too expensive and you're left with a car you don't want to drive anymore.
So don't chase the unicorn horn of 400HP or whatever. See how 200HP treats you, and if it's still not enough, make 250 or 300 your goal, but know it's a slippery slope.
I'm only planning on no more than 270HP because that's double the stock GSL-SE's 135HP, but I might not get there because I'm having way too much fun at stock S5 wastegate spring pressure of 7psi or so. Actually just today I read something in the FC section where a guy stated the S4 and S5 are both at 5.5psi and the S5 has some sort of boost solenoid controlled by the ECU which gets it closer to 9psi. That's the first time I've ever seen that info, so no way to know whether it's true. Heck maybe my setup with a stock wastegate size, which is known to be small, and a full 3" exhaust, is experiencing boost creep.
Here's a link. https://www.rx7club.com/2nd-generati.../#post11856428