half bridge 12A, with a twist
02-27-11, 01:27 PM
#51
But then you can't use two piece apex seals.
I have enough makin's to make a full bridge 13B 4-port except for the intake manifold, so I may actually go this route. I don't think 210hp is quite enough anymore. (210 HBP horsepower is waaay different than 210 streetport HP... lots more area in the curve)
But I keep going back to something soul assassin posted about nine years ago after he went fullbridge on his FC, and the subject of "what port" came up.... https://www.rx7club.com/showpost.php...9&postcount=12
Then again he also drove his car as a daily driver too, if you're going to spend a few hours a day in a car you want it to be a pleasant experience, you know?
I have enough makin's to make a full bridge 13B 4-port except for the intake manifold, so I may actually go this route. I don't think 210hp is quite enough anymore. (210 HBP horsepower is waaay different than 210 streetport HP... lots more area in the curve)
But I keep going back to something soul assassin posted about nine years ago after he went fullbridge on his FC, and the subject of "what port" came up.... https://www.rx7club.com/showpost.php...9&postcount=12
Then again he also drove his car as a daily driver too, if you're going to spend a few hours a day in a car you want it to be a pleasant experience, you know?
Just my 2 Eurocents...
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03-01-11, 05:26 PM
#52
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his seems almost off topic to post in the thread, but i thought of something.
most of our "forum" tuning is us telling the engine what we want it to do, IE we give it paul yaws timing, and fuel must be 13.1234AFR, and weather it works or not, we do it.
ive learned with the P port, that this doesn't work, the P port, is more like european politics.
tuning the P port is a balance between what i want, what the engine wants, what the neighbors will tolerate and what the carb is capable of doing.
what the engine wants; you can give a stock port anywhere from 10:1 to 16:1 afr and it will still run, the P port this window is much smaller.
so examples. i got the carb to deliver about 14.5:1 from idle to 2500rpm, i'm fine with this, the engine is ok with it (it didn't like being leaner though), there are no clouds of smoke, and its not too stinky, so the neighbors are ok with it.
i want a muffler, the neighbors want three mufflers, the engine doesn't want any!
WOT mixture; i want low 12's. the carb will either give me 12.8, which the engine likes but i feel is too lean. or the carb delivers mid 11's (i'm in between jets ). for the trackday, i chose mid 11's and the engine was ok with that. the neighbors were very happy, as the car wasn't anywhere nearby.
anyways with your 1/2 bridge, be prepared to spend a lot of time with the carb, i also suggest you try all the jets you have. the combo ive ended up with on the PP is WAY different than any of the charts ive seen, i think i'm running more fuel pressure
have fun!
mike
most of our "forum" tuning is us telling the engine what we want it to do, IE we give it paul yaws timing, and fuel must be 13.1234AFR, and weather it works or not, we do it.
ive learned with the P port, that this doesn't work, the P port, is more like european politics.
tuning the P port is a balance between what i want, what the engine wants, what the neighbors will tolerate and what the carb is capable of doing.
what the engine wants; you can give a stock port anywhere from 10:1 to 16:1 afr and it will still run, the P port this window is much smaller.
so examples. i got the carb to deliver about 14.5:1 from idle to 2500rpm, i'm fine with this, the engine is ok with it (it didn't like being leaner though), there are no clouds of smoke, and its not too stinky, so the neighbors are ok with it.
i want a muffler, the neighbors want three mufflers, the engine doesn't want any!
WOT mixture; i want low 12's. the carb will either give me 12.8, which the engine likes but i feel is too lean. or the carb delivers mid 11's (i'm in between jets ). for the trackday, i chose mid 11's and the engine was ok with that. the neighbors were very happy, as the car wasn't anywhere nearby.
anyways with your 1/2 bridge, be prepared to spend a lot of time with the carb, i also suggest you try all the jets you have. the combo ive ended up with on the PP is WAY different than any of the charts ive seen, i think i'm running more fuel pressure
have fun!
mike
03-01-11, 07:03 PM
#53
Yes, even I still recommend the Paul Yaw 10° split for 13B and 8° for 12A, even though I tend to time my 12As at 10° split because of the horror stories of 12As breaking trailing plug porcelain at 8 degrees at high RPM and stuff. Like most recently just a day or two ago I marked a 12A pulley for a 10° split, but may still time it for 8°. Old habits die hard. (this is on the 12A I just completed. The half BP will probably get the same 10° split marking)
I'm sure I'll test all the jets I have. I've got some 170s and 150s for the secondaries and also some stock 120 secondary air bleeds from a 6 port 12A carb. I don't have an O2 sensor installed yet, but I might go ahead and add a bung if this engine stays in the FB for any length of time (it's for a local guy so I might leave the final tuning up to him).
I'm just glad I have some prepping on Nikkis so I'll be able to jump right in with jet and air bleed changes without having to spend (waste?) time on the forums, until I get it to run well. I'll even change the secondary slow air bleeds and primary slow air bleeds to get the idle where it's within the range of the air and fuel mixture screws for easier idle adjustments down the road as it continues to break in. Oh, I guess the sec slow air bleeds can stay as they are because it's getting mech secs and the vacuum diaphram housing will be removed... unless the sec slow air bleeds affect primary running in some way? All my reading hasn't answered that question. Do you happen to know? Sterling is MIA right now so just wondering (don't want to bother him).
As for the brake booster fitting, I was going to test it on one of the primary runners, but Mike doesn't think it's necessary as his 20B was fine with just a little 3.5mm nipple pulling vacuum from the back of the UIM. Mine used one on the side and worked fine. So instead of going through the trouble of adding a nipple, I'll start by using the stock booster fitting. The manifold has full separate runners so it should be fine. I think all FBs have a built in check valve too. Ask hyper4 mance2k about that.
Hey Mike, what year is the chassis occupied by peepers? I'll be testing the half BP in an '81. I think '81 was the first model year that upped the size of the booster from the smaller SA/old school size. Then they stayed unchanged to at least '83. Then the 84-85 changed again.
I'm sure I'll test all the jets I have. I've got some 170s and 150s for the secondaries and also some stock 120 secondary air bleeds from a 6 port 12A carb. I don't have an O2 sensor installed yet, but I might go ahead and add a bung if this engine stays in the FB for any length of time (it's for a local guy so I might leave the final tuning up to him).
I'm just glad I have some prepping on Nikkis so I'll be able to jump right in with jet and air bleed changes without having to spend (waste?) time on the forums, until I get it to run well. I'll even change the secondary slow air bleeds and primary slow air bleeds to get the idle where it's within the range of the air and fuel mixture screws for easier idle adjustments down the road as it continues to break in. Oh, I guess the sec slow air bleeds can stay as they are because it's getting mech secs and the vacuum diaphram housing will be removed... unless the sec slow air bleeds affect primary running in some way? All my reading hasn't answered that question. Do you happen to know? Sterling is MIA right now so just wondering (don't want to bother him).
As for the brake booster fitting, I was going to test it on one of the primary runners, but Mike doesn't think it's necessary as his 20B was fine with just a little 3.5mm nipple pulling vacuum from the back of the UIM. Mine used one on the side and worked fine. So instead of going through the trouble of adding a nipple, I'll start by using the stock booster fitting. The manifold has full separate runners so it should be fine. I think all FBs have a built in check valve too. Ask hyper4 mance2k about that.
Hey Mike, what year is the chassis occupied by peepers? I'll be testing the half BP in an '81. I think '81 was the first model year that upped the size of the booster from the smaller SA/old school size. Then they stayed unchanged to at least '83. Then the 84-85 changed again.
03-01-11, 11:39 PM
#56
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Hey Mike, what year is the chassis occupied by peepers? I'll be testing the half BP in an '81. I think '81 was the first model year that upped the size of the booster from the smaller SA/old school size. Then they stayed unchanged to at least '83. Then the 84-85 changed again.
03-02-11, 12:33 AM
#58
Originally Posted by 84stock
I would tap the primary and secondary runner (1 each) with a vac fitting. Easier while it's apart and you would have the opportunity to hook a vac gauge to wither when you test drive to prove some of your theories.
03-02-11, 12:53 AM
#59
Old [Sch|F]ool
I know that using a half bridge as described to keep the apex seal corner pieces towards the center may be beneficial. But a well cut full bridge will not damage corner pieces. I drove a full bridge engine daily for over 50k and had no problems with abnormal wear or damage on the corner pieces. So lets just knock that "myth" right out of this thread. The key is ensuring that the bridge is wide enough to spread the spring tension over a wide area of the seal, Any more timing or opening to make up for the wide bridge can be gotten if you j-port towards the water seal.
Just my 2 Eurocents...
(thread jack disengaged)
Just my 2 Eurocents...
(thread jack disengaged)
You're saying you used the two piece seals with a full bridge? How wide were the bridges? (the strips of metal, not the eyebrows) I've been using 5mm.
I hear what you're saying and I'm listening. But, I've also seen and been told that the corner piece must never be allowed to run against a bridge, even an unrelieved one. This never quite made sense to me since the way the seal would have to angle to spread out into the eyebrow seemed impossible, but the people saying this had a lot more rotary experience than I had, so I just ran with it.
I say this because I have been contemplating a full bridge 12A but the price of carbon seals has been the sticking point. If I can use the 2-piece seals then this greatly simplifies my operation! I would only relieve the secondary ports (not as far as a J-bridge, personally - have had enough fun keeping coolant in an engine without having to worry about a breached water jacket) and not the primaries.
So - innnnteresting.
Jeff - Remember 10 years ago or so, the first street port I did? I modified the shutter valve style intake to be a four-hole intake, no runners. The bottom end torque was incredible, to say the least. Unfortunately, I discovered that the channels are important because the primary runners can't flow everything that the primary barrels can, and vice-versa for the secondaries. I later took that same manifold, cut channels into it to make it look like a 79-80 manifold, and went almost as fast on a stock port engine. In a heavier car. Through a muffler, not open header (which was worth half a second plus in the street port). So, er... let's see what happens!
03-02-11, 12:55 AM
#60
Old [Sch|F]ool
ive learned with the P port, that this doesn't work, the P port, is more like european politics.
tuning the P port is a balance between what i want, what the engine wants, what the neighbors will tolerate and what the carb is capable of doing.
what the engine wants; you can give a stock port anywhere from 10:1 to 16:1 afr and it will still run, the P port this window is much smaller.
so examples. i got the carb to deliver about 14.5:1 from idle to 2500rpm, i'm fine with this, the engine is ok with it (it didn't like being leaner though), there are no clouds of smoke, and its not too stinky, so the neighbors are ok with it.
i want a muffler, the neighbors want three mufflers, the engine doesn't want any!
tuning the P port is a balance between what i want, what the engine wants, what the neighbors will tolerate and what the carb is capable of doing.
what the engine wants; you can give a stock port anywhere from 10:1 to 16:1 afr and it will still run, the P port this window is much smaller.
so examples. i got the carb to deliver about 14.5:1 from idle to 2500rpm, i'm fine with this, the engine is ok with it (it didn't like being leaner though), there are no clouds of smoke, and its not too stinky, so the neighbors are ok with it.
i want a muffler, the neighbors want three mufflers, the engine doesn't want any!
03-02-11, 03:14 AM
#61
I actually do remember that, and it was the inspiration I used when cutting channels in a couple of 74-75 13B intake manifolds. Only later I discovered that it's not strictly necessary if for one the carb was originally calibrated for a separate runner manifold, and two if the manifold itself is a high flow design, not some poor excuse like the crappy 79-80 or the even worse 81-85. The best 4 port manifolds ever made range from 71 to 78. Then choose channeled or sep runner based on the carb's original matched setup, otherwise the idle will be weird and can't really be tuned far enough with the air and fuel screws to correct it (this is due to the size of the vertical slits in the cast iron TB which aren't really resizeable).
I did get decent results from an 81-85 manifold after removing the shudder valve and cutting a channel. It still wasn't as awesome as a real channeled 77-78 manifold, though. That was quite a summer.
I guess what I'm saying is if you've got a matched setup (carb and mani) that was channeled from the factory, keep it that way. Likewise if separate runner, keep it separate. But if you're into experimenting, go for it. I just know for sure that the manifold above will stay separated and only the secondary ports will be bridged. Doing it any other way doesn't make a lick of sense.
I did get decent results from an 81-85 manifold after removing the shudder valve and cutting a channel. It still wasn't as awesome as a real channeled 77-78 manifold, though. That was quite a summer.
I guess what I'm saying is if you've got a matched setup (carb and mani) that was channeled from the factory, keep it that way. Likewise if separate runner, keep it separate. But if you're into experimenting, go for it. I just know for sure that the manifold above will stay separated and only the secondary ports will be bridged. Doing it any other way doesn't make a lick of sense.
03-02-11, 03:23 PM
#62
My idea would be a racing beat intake (it's channeled), a 4 hole spreadbore adapter, and a holley spreadbore with the large secondaries feeding the thirsty bridged secondaries. Notice the carb is channeled primary to primary and secondary and secondary.
03-03-11, 01:29 PM
#63
Ah yes I remember your beautiful quadrapuke. 
Too bad they're so rare because that's like the perfect two sizes for a nice street performing rotary with monster secondaries. Probably about as rare as an old school Nikki like mine above.
Fixed that for yah! Unless you cut channels in your RB mani or added a spacer with channels?
All Nikkis are believed to have a channel connecting both primaries together at the lowest point on the TB. This allows the air fuel screws to adjust for both barrels. But I think both secondaries are always separate.
Hmm, aren't all Holleys channeled like your quadrapuke? I only have three here to look at but only one has easy access before I install it on the (now fixed) 7" Camden later today. I also should look up under an Edlebrock if I remember.
Too bad they're so rare because that's like the perfect two sizes for a nice street performing rotary with monster secondaries. Probably about as rare as an old school Nikki like mine above.
Originally Posted by 84stock
My idea would be a racing beat intake (it's fully separate)
All Nikkis are believed to have a channel connecting both primaries together at the lowest point on the TB. This allows the air fuel screws to adjust for both barrels. But I think both secondaries are always separate.
Hmm, aren't all Holleys channeled like your quadrapuke? I only have three here to look at but only one has easy access before I install it on the (now fixed) 7" Camden later today. I also should look up under an Edlebrock if I remember.
03-03-11, 01:52 PM
#64
I have a question about vacuum advance. I've never messed around with it because I've never had a fully stock engine. lol But would it be a good idea to incorporate it on the half BP? I ask because the primary side will be stock (maybe with cleaned up runners or casting flash smoothed but definitely stock timing to match the manifold runner length and carb venturis etc). Would having vacuum advance help or hurt performance when the secondaries open up? I ask because I've never experiemented with it. I've only ever done mechanical (centrifugal) advance on engines ranging from stock ports up to extend/extreme streetports. Mech advance only has always worked perfectly. But am I missing out on some low end torque and/or gas mileage? Thanks.
03-06-11, 01:35 AM
#66
I just got the engine in the car today (not the half BP). Found out my clutch master went bad so I ordered one from RockAuto. Otherwise I'll make progress at a good rate between rain storms. You don't need a clutch to test fire an engine.
03-06-11, 01:07 PM
#68
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I have a question about vacuum advance. I've never messed around with it because I've never had a fully stock engine. lol But would it be a good idea to incorporate it on the half BP? I ask because the primary side will be stock (maybe with cleaned up runners or casting flash smoothed but definitely stock timing to match the manifold runner length and carb venturis etc). Would having vacuum advance help or hurt performance when the secondaries open up? I ask because I've never experiemented with it. I've only ever done mechanical (centrifugal) advance on engines ranging from stock ports up to extend/extreme streetports. Mech advance only has always worked perfectly. But am I missing out on some low end torque and/or gas mileage? Thanks.
i'm sure you are missing a little low end/response, but the better the VE the less you need the vacuum advance.
its definitely something to play with
03-07-11, 09:56 PM
#69
Originally Posted by 84stock
This project is like a gorgeous virgin that wants to wait until after the wedding.
Ok the first engine runs nicely now. Got it to idle at 725-750rpm on a Nikki I borrowed from a friend. Next move is to strip/clean and test run the old school carb and manifold.
03-07-11, 10:02 PM
#71
I have new plans for the 83 fb project now. Was debating between the 12a and 13b thing. It has 121,000 km with a coolant seal leak and I decided to keep it 12a to preserve some originality especially since I can likely get away with just a soft seal kit. And to sweeten the plan, i scored a light steel flywheel (off an 84), healthy clutch & pressure plate (5,000 km on it) and a racing beat intake all for, now are you ready....
$100.00
and it was local!!!
$100.00
and it was local!!!
03-08-11, 08:18 PM
#74
It's in and working (now I can feel that I've got a stock pressure plate in there where before it was so stiff, right before it failed, that it felt like a typical RB street strip!). I could technically take it for a test drive right now, but I'm going to concentrate instead on getting the old school carb up and working.