Dual Plane Fuel Distribution

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Valman

Valman

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On dual plane intakes on a few occasions, I’ve seen that the higher plenum side can show a richer mixture on the plugs than the lower plenum side.

Seems to depend on what carb & spacer you use, if you open the divider or not etc. I’m seeing a bit of this ATM, not a radical difference, but noticeable. I’m running an adapter on an Eddy RPM with an open phenolic spacer (3/4’’). With an 850cfm TQ on top. Interested what other guys have done to get around it. I’ve done stagger jetting in the past, but that’s kind of a band aid.

A penny for your thoughts on it..:) Pic of manifold / adapter / spacer.

IMG_0086.jpeg
 
Stuff Kleenex or paper towel in the side that's getting too much fuel. That ought even up fuel distribution.
 
We run Dual Plane production manifolds on our
Stock Eliminator and some of our street stuff.

We have ourselves not noticed much difference in the
exhaust gas temps between different cylinders although
it makes sense to me it might do so considering the geometry
of the intake.

We ourselves have never found any benefit to stagger jetting the
Thermoquad in either a dual plane or a single plane intake.

Most of our experiences is with small block applications although
we race a 400 in Stock with a 400 and our experience was similar.

Now on a manifold with a huge difference in passage length such as
a Max Wedge, we definitively stagger jet the AFB carbs.

My .02 worth = for Free!
 
Plug coloring was how I accidentally noticed the difference in distribution as well in my 360. I believe it was a 2# difference that corrected it. But this was with a Weiand Stealth, Canton 1" tapered 4-hole phenolic spacer and a square jetted Holley DP. The sides were isolated from each other. It's been a while but I believe I picked up around .05 in ET. However, a single plane Holley Strip Dominator was still faster in my particular application.

Stagger jetting side-to-side is easiest to compensate but it will involve more of a visual trial & error or using sensors because of the spread bore design. Also, the bigger the "window" between dual plane plenums (i.e.: thick, open gaskets, open spacer and/or cut down divider) there will theoretically be more air flow sharing that can reduce the A/F ratio difference between the sides.
 

My modest DailyDriver 11/1Scr 367 has the AG with a 750DP on it.
Plugs had over 50,000 on them when the car went 93 in the Eighth.
Those plugs went another 50,000.
I can't read street plugs.
But-um, I run her at a solid 207F, and on 87E10, so that might have something to do with it.
The Coil is an old Accell square-top, new in 1999.

But one thing about a TQ that may be worth mentioning is that the metering-rod holder doesn't always sit square to the base of the carb .......
and depending on how high you have them set, and where on the taper they are running, at Part Throttle, I can imagine them running a lil wonky.
 
Locomotion said:
Plug coloring was how I accidentally noticed the difference in distribution as well in my 360. I believe it was a 2# difference that corrected it. But this was with a Weiand Stealth, Canton 1" tapered 4-hole phenolic spacer and a square jetted Holley DP. The sides were isolated from each other. It's been a while but I believe I picked up around .05 in ET. However, a single plane Holley Strip Dominator was still faster in my particular application.

Stagger jetting side-to-side is easiest to compensate but it will involve more of a visual trial & error or using sensors because of the spread bore design. Also, the bigger the "window" between dual plane plenums (i.e.: thick, open gaskets, open spacer and/or cut down divider) there will theoretically be more air flow sharing that can reduce the A/F ratio difference between the sides.
Click to expand...
I may try taking off the phenolic spacer and try the thick TQ heat insulator gasket, see if that evens the plug colouring.
 
GTX JOHN said:
We have ourselves not noticed much difference in the
exhaust gas temps between different cylinders although
it makes sense to me it might do so considering the geometry
of the intake.
Click to expand...
I’m thinking that there probably isn’t much difference in the mixture, but the deeper plenum side has an effect on providing a finer, more homogenous mixture. Then showing slightly leaner on the plug.
The deeper plenum side also sits lower in the ‘V’, so probably hotter on that side as well. Great info, thank you!
 
The lower plenum has more air volume that the carb signal has to fight through, so not surprised that it may need slightly richer jetting than the upper plenum. But have also seen the reverse...
Something else you could try: production TQs had the top of the air valve bent forward. Comp Series had it straight. If you have TQ parts you could try this because it would have some effect on airflow.
 
Bewy said:
Comp Series had it straight. If you have TQ parts you could try this because it would have some effect on airflow
Click to expand...
I do have a spare secondary air valve from a junk carb that I re-plated. Could give it a go, would you have a pic of a C.S air valve? Thanks for the info.
Click to expand...
 
Might have a pic in a book/magazine. Will have a look. It differs in two ways from the production carb:
- the front of the AV is straight, not bent, like the production TQ, as described above. What that does in practical terms is more air is entering the carb during the initial rotation of the AV. May also increase total airflow slightly, & reduce turbulence because the bent section is gone.
- does not have the opening in the AV for the choke linkage. I remove all that linkage & braze a small plate over the opening.

If you try & remove the AV screws, you will likely snap them off because they are staked. Grind the thread down flush to the shaft & they will come out easily with a 3/16" spanner. Loctite the screws back in place.

Steve Dulcich flow tested the 850 [ He says 'we' & I think that is when he worked with D. Vizard ], reckoned they flowed over 900 cfm in stock form..

img398.jpg
 

Valman said:
On dual plane intakes on a few occasions, I’ve seen that the higher plenum side can show a richer mixture on the plugs than the lower plenum side.

Seems to depend on what carb & spacer you use, if you open the divider or not etc. I’m seeing a bit of this ATM, not a radical difference, but noticeable. I’m running an adapter on an Eddy RPM with an open phenolic spacer (3/4’’). With an 850cfm TQ on top. Interested what other guys have done to get around it. I’ve done stagger jetting in the past, but that’s kind of a band aid.

A penny for your thoughts on it..:) Pic of manifold / adapter / spacer.

View attachment 1716394576
Click to expand...
On the dyno we use egts, sparkplugs and O2's as an indication of fuel distribution. They are just indicators and not gospel. I don't know how you're doing your testing but this might be something to consider.

Idle mixture, cruise mixture and full throttle mixture can each have it's own air/fuel ratio and distributon characteristics. On top of that even if you are looking just at wide open throttle at full load the distribution and air/fuel ratio can change throughout the rpm range. I'm saying this to get get your and others ideas about reading spark plugs and how they control for these variables when reading spark plugs. Admitingly I am weak at best when it comes to reading sparkplugs. I usually use it as a confirmation to what I think I might be seeing with egts and o2s.

I'm not saying that tuning can't be done to improve fuel distribution for individual cylinders. We do it alot at the dyno. We employ various methods to do so and when it works often you are rewarded with a bump in power or a smoother running engine.

Some of things we have done to improve fuel distribution are:

Add a spacer and or different types of spacers. If it already has a spacer take the spacer out. Some spacers are adjustable. Sliding them around might help.

Air cleaner bases and lids can change fuel distribution and air/fuel ratio. How tall the filter is can also have an effect. Especially very short filters used for hood clearance.

Try a different carburetor. Carburetors, even the same part number can have different distribution characteristics. Stagger jetting.

Bending, twisting, notching, shifting and changing boosters and or booster type.

Changing to a different or modifying the intake manifold. Seems like the dual planes are more challenging.

If anyone else has some tricks or ideas on how to change distribution that has worked for them please share.
 
I agee. At low rpm with low throttle, the fuel distribution has a lot to do with the vacuum and reversion if there is some. Wide open throttle, full load, fuel distribution is going to have a lot to do with the air flow and paths. At mid throttle positions mixing and flow can be different...
Another factor which is harder to fiure on is whether the distribution in the chamber is good. This gets into the same area as such as spark plug indexing to minimize shadows.

Keeping with just the issue of high flow distribution, your choices are stagger jetting, notches and spivies on the boosters, and working the intake (dams and removing material). Experimenting with stagger jetting and spivies are the easiest options. There's examples of all three in the Direct Connection racing tips, but of course none are for the Performer RPM.

www.tapatalk.com

racingfuelsystems-Spivy

Spivy It isn’t necessary to use such a large tie-wrap as in these pictures. Those just happened to be what was available close at hand in that dyno
www.tapatalk.com www.tapatalk.com
Thank's to tapatalk the photos are gone but the text is all there.
 
Valman,
Below is the pic of the CS TQ air valve. You can see it is straight, not bent.
Were you at E/Creek a few weeks ago wearing a TQ T shirt? If so you were talking to Peter who has a factory TQ on his 455 LeMans. AV has been modified as described. His car ran 119 mph. 3.36 axle, T400, street radial tyres, 3950 # without driver. Sol Lifter roller cam, idles in gear @900 with enough vac for power brakes. Oh...& it has a rev pattern cam [ less exh ], [ you know, the ones they say don't work..... ]. With 48* of timing at idle, it ran so cool he had to run the engine in the staging lanes to get heat into it....while others were using leaf blowers to cool their engines!! He could never get enough runs to experiment trackside with shift rpm, tyre pressure, ign timing or adjustments on the TQ. I am quite sure it would have run 120 mph, maybe more...

When these products were released for sale, many were supplied to magazine editors for testing. I have one of those mags & there is a pic of the CSTQ sitting on a 426 Hemi. The manifold is a cross ram with removable top; they claim when the baffle in the secs was removed, it picked up 30hp!
 
Bewy said:
Were you at E/Creek a few weeks ago wearing a TQ T shirt
Click to expand...
No, wasn’t me but I do have a TQ T-shirt! Haven’t been to Eastern Creek for a little while now. If I do go there, it’s usually to circuit racing events nowadays.

I don’t think the photo uploaded mate..
 
Bewy said:
CSTQ sitting on a 426 Hemi. The manifold is a cross ram with removable top
Click to expand...
I remember seeing an article once where the Hemi was the engine Carter & Chrysler tested the TQ on. Possibly the 404ci ‘ball-stud’ hemi?? Going off memory, which might be hazy
 
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