Is there a ported vacuum port on the Nikki? What have YOU tried timing?
09-08-09, 09:49 PM
#1
Is there a ported vacuum port on the Nikki? What have YOU tried timing?
So I've got an '82 GSL here. Motor was rebuilt and installed by Pineapple racing. They had the vacuum pods hooked to manifold vacuum.
Seems some of the older wise folk have theirs hooked to Ported.
I am putting a pre shutter valve intake on mine and wondering if there is a ported vacuum port on the carb itself? I plan to ditch the spacer plate in favor of a custom higher rise spacer. Just to see if I can gain some velocity.
When I took the rats nest off the car still LOVED manifold vacuum. Idles Awesome at 600. Plenty of adjustment in the mixture screw. NO vacuum leaks.
So after getting a headache reading the "why did mazda retard timing on carbed cars" post.... I thought I'd try it out and see for myself.
Since this is the only Rotary I've ever had I don't know that much about timing. I know how ported AND manifold vacuum work and effect vacuum advance. All the V-Engines I've ever owned with any performance or worked on (Work in a Hotrod shop) run way better on Manifold Vacuum. Typically because of larger camshafts needing the extra timing to idle properly. My 12A is a stock port... so maybe ported will help that low end grunt?
Any REAL LIFE input here? Not just theory? Who's tried what and what's worked for them? I'm used to setting a non vacuum total timing, then putting the vacuum advance where the motor likes it. This is new to me. Car runs **** though as it is now!
Seems some of the older wise folk have theirs hooked to Ported.
I am putting a pre shutter valve intake on mine and wondering if there is a ported vacuum port on the carb itself? I plan to ditch the spacer plate in favor of a custom higher rise spacer. Just to see if I can gain some velocity.
When I took the rats nest off the car still LOVED manifold vacuum. Idles Awesome at 600. Plenty of adjustment in the mixture screw. NO vacuum leaks.
So after getting a headache reading the "why did mazda retard timing on carbed cars" post.... I thought I'd try it out and see for myself.
Since this is the only Rotary I've ever had I don't know that much about timing. I know how ported AND manifold vacuum work and effect vacuum advance. All the V-Engines I've ever owned with any performance or worked on (Work in a Hotrod shop) run way better on Manifold Vacuum. Typically because of larger camshafts needing the extra timing to idle properly. My 12A is a stock port... so maybe ported will help that low end grunt?
Any REAL LIFE input here? Not just theory? Who's tried what and what's worked for them? I'm used to setting a non vacuum total timing, then putting the vacuum advance where the motor likes it. This is new to me. Car runs **** though as it is now!
09-09-09, 12:06 AM
#2
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mazda had emissions to meet.
the only 12A i've played with this on is a PP, the rest are 13B/20B's, but idle timing usually ends up in the 0-5 btdc range, higher doesnt make much difference?
they DO like more timing in the midrange/top end.
the only 12A i've played with this on is a PP, the rest are 13B/20B's, but idle timing usually ends up in the 0-5 btdc range, higher doesnt make much difference?
they DO like more timing in the midrange/top end.
09-09-09, 06:08 AM
#3
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Ported vacuum? Just find a nipple that shows no vacuum at idle, but does show vacuum when the throttle is opened. I believe the 1st and/or 2nd nipple from the front of the car is ported vacuum.
I switched to ported a couple of years ago, and it really seemed to improve the low end grunt. Car idles fine.
There have been several people who have driven my car, and none have had any complaints in regards to the power my little 12a is putting out. But this is still a very touchy topic, and many people will argue with me over which setup is best.
I simply advise people to try it both ways, and see which one you like. Just keep in mind that if you change the vacuum source, the timing at idle will also change. So, you might have to retime the motor, and maybe even play with idle tuning and speed. But if you do it right, and try it out, I'm sure you will be happy with the improvements.
.
I switched to ported a couple of years ago, and it really seemed to improve the low end grunt. Car idles fine.
There have been several people who have driven my car, and none have had any complaints in regards to the power my little 12a is putting out. But this is still a very touchy topic, and many people will argue with me over which setup is best.
I simply advise people to try it both ways, and see which one you like. Just keep in mind that if you change the vacuum source, the timing at idle will also change. So, you might have to retime the motor, and maybe even play with idle tuning and speed. But if you do it right, and try it out, I'm sure you will be happy with the improvements.
.
09-09-09, 06:39 AM
#4
Nikki-Modder Rex-Rodder
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Making the spacer thicker isn't going to have much impact. -Not nearly as much as porting the stock manni or fitting the Nikki to a RB Holley manni.
Gains from "velocity stacks" and intake manni length increase are higher in engines that have much lower power bands than the rotary (like V-8s). The rotary is already flowing a great deal of velocity while in it's power band, so such efforts yield only minor gains.
Gains from "velocity stacks" and intake manni length increase are higher in engines that have much lower power bands than the rotary (like V-8s). The rotary is already flowing a great deal of velocity while in it's power band, so such efforts yield only minor gains.
09-09-09, 09:42 AM
#5
Are you still refering to the spacer plate with all the nipples or on the carb itself? I was looking to ditch the spacer plate to eliminate potential vacuum leaks.
Originally Posted by Sterling
Making the spacer thicker isn't going to have much impact. -Not nearly as much as porting the stock manni or fitting the Nikki to a RB Holley manni.
Gains from "velocity stacks" and intake manni length increase are higher in engines that have much lower power bands than the rotary (like V-8s). The rotary is already flowing a great deal of velocity while in it's power band, so such efforts yield only minor gains.
Gains from "velocity stacks" and intake manni length increase are higher in engines that have much lower power bands than the rotary (like V-8s). The rotary is already flowing a great deal of velocity while in it's power band, so such efforts yield only minor gains.
I will be removing some bump passageways in the intake tract. Aluminum welding is fun!
09-09-09, 11:40 AM
#6
Nikki-Modder Rex-Rodder
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I don't know.
I've always read the same thing.
Jeff20B knows a bit about that, I think. But good flow gains can be had by removing the bumps, like you said, as well as opening up the mid parts of the runners. -Enough to make it worthwhile, anyway.
Flow wise, nothing will beat Racing beats Holley manifold, though. I believe is is port-matched. I'd have to go dig mine up to look.
I've always read the same thing.
Jeff20B knows a bit about that, I think. But good flow gains can be had by removing the bumps, like you said, as well as opening up the mid parts of the runners. -Enough to make it worthwhile, anyway.
Flow wise, nothing will beat Racing beats Holley manifold, though. I believe is is port-matched. I'd have to go dig mine up to look.
09-09-09, 11:54 AM
#7
The RB Holley manifolds typically have short intermediate runners. This mismatch helps reduce reversion waves that would otherwise screw with idle quality. At high RPM it is less of an issue. Case in point are the '76 reverse runner manifolds. The primaries run to the end plates and the secondaries run to the intermediate plate; the secondary runners are quite large in diameter, short in length and tall where they enter the engine. This works because they only are used at high RPM when the carb secondaries open. Mazda kept the intermediate ports tall in later years to keep compatability with the reverse runner manifolds, but they also found it worked fine with normal runner manifolds.
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09-09-09, 01:23 PM
#8
I thought I'd try this intake before hitting the RB one. Since this mod only costs me an intake gasket and some welding material.
So smooth out the intake bumps, leave it rough so the fuel doesn't wet out, and don't port match the primaries. CORRECT?
As far as timing goes.... Ported or Manifold? Setting timing if manifold, set to the marks w/ or w/o vacuum on the pods.
Then, is there any benefit to increasing or decreasing base timing?
So smooth out the intake bumps, leave it rough so the fuel doesn't wet out, and don't port match the primaries. CORRECT?
As far as timing goes.... Ported or Manifold? Setting timing if manifold, set to the marks w/ or w/o vacuum on the pods.
Then, is there any benefit to increasing or decreasing base timing?
09-09-09, 02:27 PM
#9
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I thought I'd try this intake before hitting the RB one. Since this mod only costs me an intake gasket and some welding material.
So smooth out the intake bumps, leave it rough so the fuel doesn't wet out, and don't port match the primaries. CORRECT?
As far as timing goes.... Ported or Manifold? Setting timing if manifold, set to the marks w/ or w/o vacuum on the pods.
Then, is there any benefit to increasing or decreasing base timing?
So smooth out the intake bumps, leave it rough so the fuel doesn't wet out, and don't port match the primaries. CORRECT?
As far as timing goes.... Ported or Manifold? Setting timing if manifold, set to the marks w/ or w/o vacuum on the pods.
Then, is there any benefit to increasing or decreasing base timing?
so without the vacuum advances the timing at both ends is about where you want it anyways, the vacuum is just for cruising MPG, as at say 2500 rpm cruise you'd want timing in the 28-32 degree ballpark.
the info on the distributor curves are in the shop manuals, which are all online.
09-09-09, 02:58 PM
#10
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I run a Dellorto and have manifold vacuum hooked up after setting
the timing at 4K to the RB specs for the Dell. Really helps with off idle
response and the dreaded bog as well. Also improved mpg since at
cuise and low throttle the timing advances some.
The only downside is my idle hangs around 900 rpms and has a lope
to it due to the vacuum at idle but the positives far outwiegh this
one negative.
the timing at 4K to the RB specs for the Dell. Really helps with off idle
response and the dreaded bog as well. Also improved mpg since at
cuise and low throttle the timing advances some.
The only downside is my idle hangs around 900 rpms and has a lope
to it due to the vacuum at idle but the positives far outwiegh this
one negative.
09-09-09, 03:12 PM
#11
Nikki-Modder Rex-Rodder
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-There's gotta be a way to utilize one of the stock vacuum solenoid valves to get around this idle issue. (Such as, the vacuum advance from port needs to meet a certain threshold before the valve opens, so that at idle the port is closed off, allowing for a reasonable idle RPM, etc.)
I can't afford the time to find this solution, but whoever does will achieve "Carbed 12a Owner Rock Star" status! lol
I can't afford the time to find this solution, but whoever does will achieve "Carbed 12a Owner Rock Star" status! lol
09-09-09, 03:34 PM
#12
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-There's gotta be a way to utilize one of the stock vacuum solenoid valves to get around this idle issue. (Such as, the vacuum advance from port needs to meet a certain threshold before the valve opens, so that at idle the port is closed off, allowing for a reasonable idle RPM, etc.)
I can't afford the time to find this solution, but whoever does will achieve "Carbed 12a Owner Rock Star" status! lol
I can't afford the time to find this solution, but whoever does will achieve "Carbed 12a Owner Rock Star" status! lol
09-09-09, 06:03 PM
#13
I run a Dellorto and have manifold vacuum hooked up after setting
the timing at 4K to the RB specs for the Dell. Really helps with off idle
response and the dreaded bog as well. Also improved mpg since at
cuise and low throttle the timing advances some.
The only downside is my idle hangs around 900 rpms and has a lope
to it due to the vacuum at idle but the positives far outwiegh this
one negative.
the timing at 4K to the RB specs for the Dell. Really helps with off idle
response and the dreaded bog as well. Also improved mpg since at
cuise and low throttle the timing advances some.
The only downside is my idle hangs around 900 rpms and has a lope
to it due to the vacuum at idle but the positives far outwiegh this
one negative.
09-09-09, 11:04 PM
#14
Rechecked mine tonight. It's a Cali car, no rats nest. Hooked by diagram to the 2nd nipple from the left. It's indeed ported. Calls for 20 trailing, 0 leading. RB says 19 trailing, -2 leading. So I set it that way, we'll see how it goes!
Could have sworn it was on manifold vacuum. Oh well. Looks like the spacer plate stays!
Was hoping to find more milage! I only tick off 18mpg combined mostly city. And I don't redline THAT often!
Could have sworn it was on manifold vacuum. Oh well. Looks like the spacer plate stays!
Was hoping to find more milage! I only tick off 18mpg combined mostly city. And I don't redline THAT often!
09-10-09, 10:21 AM
#15
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I use ported vacuum because then there is no advance at idle. However, as soon as you tip into the throttle, the advance starts coming in. This results (I feel) in much more low end grunt than the other method (manifold vacuum).
This is because, with manifold vacuum, you are getting all of your advance at idle. Then, once you tip into the throttle, the timing starts retarding right away. This can result in bogging, and loss of that low end grunt that I mentioned earlier.
Anyway, this is an argument that has gone on for years now. Like I said before, just try it both ways and see what you like the best...
This is because, with manifold vacuum, you are getting all of your advance at idle. Then, once you tip into the throttle, the timing starts retarding right away. This can result in bogging, and loss of that low end grunt that I mentioned earlier.
Anyway, this is an argument that has gone on for years now. Like I said before, just try it both ways and see what you like the best...
07-19-10, 09:51 PM
#17
I use ported vacuum because then there is no advance at idle. However, as soon as you tip into the throttle, the advance starts coming in. This results (I feel) in much more low end grunt than the other method (manifold vacuum).
This is because, with manifold vacuum, you are getting all of your advance at idle. Then, once you tip into the throttle, the timing starts retarding right away. This can result in bogging, and loss of that low end grunt that I mentioned earlier.
Anyway, this is an argument that has gone on for years now. Like I said before, just try it both ways and see what you like the best...
This is because, with manifold vacuum, you are getting all of your advance at idle. Then, once you tip into the throttle, the timing starts retarding right away. This can result in bogging, and loss of that low end grunt that I mentioned earlier.
Anyway, this is an argument that has gone on for years now. Like I said before, just try it both ways and see what you like the best...
(hate to bump an old thread)
So did you have to plug the vacuum line to the vacuum advance when you set the base timing? the FSM isn't clear on it IMHO.
07-20-10, 10:47 AM
#18
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If using manifold vacuum, then yes you need to disconnect and plug the vacuum source.
If using ported vacuum, then no. It only starts to affect things once you open the throttle.
If using ported vacuum, then no. It only starts to affect things once you open the throttle.
07-22-10, 07:33 AM
#20
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If you are using manifold vacuum, then you do need to. Manifold vacuum means that the system is seeing vacuum at idle, which will be advancing the timing.
This is assuming that the rat's nest has been removed. If the nest is still in place, then there will be a solenoid in place to prevent this.
This is assuming that the rat's nest has been removed. If the nest is still in place, then there will be a solenoid in place to prevent this.
07-22-10, 10:52 AM
#21
Yep. On a stock setup, you time with the vacuum lines intact, at idle. The FSM doesn't mention it because nothing needs to be done.
Likewise on a stock setup, when setting idle & mix the only plumbing change you're supposed to make is to disconnect and plug the line for the idle compensator.
Likewise on a stock setup, when setting idle & mix the only plumbing change you're supposed to make is to disconnect and plug the line for the idle compensator.
