The Six-Pack Manifold Thread

[F-BIRD'88]

You don't need to block the outer carbs to tune the center carb.

[Aussie Chrysler]

I don't agree with that method of tuning at all. The factory designed the outboard carbs to contribute to the overall idle/part-throttle in order to keep fuel circulating and fresh in the outboards. If you tune it that way, what happens when you re-introduce the outboards to the mix? You would have to completely re-calibrate the factory design.

I would agree with keeping the outboards wired closed while tuning until you get the center carb completely dialed in, then retune full throttle with the outboards engaged.

Fair point. The author of the article seemed to think the idle circuit was to compensate for machining tolerances between the throttle blade and bore, but what you say makes sense. Luckily, it's not something I need to consider with sequential injection.

[Geoff2]

AC,
I realise you are a 6 pack fan, but don't let that cloud your judgement. If you can, take a look at a 64-66 Pontiac intake manifold that takes the Carter AFB carb. Then compare it a 67 or later Pontiac manifold that takes the QJ. You wouldn't think they were from the same engine...
The 67 manifold is a true hi-rise design, with generous, smooth passages. A quantum leap in design. Folks are using these manifolds & running low 11 sec times, & even 10s with a light car. It pains me to say it because I am a Chrysler fan, but the Chrys 4 bbl dual plane manifolds were poorly designed, it is that simple.
Also, many other companies used triple 2 bbl carbs before Chrysler did.

[Aussie Chrysler]

Obviously I'm biased! But there are plenty of big block and small block Mopar six-packs running 11s, 10s and possibly even better. Even the old Small Block 'A' Engine handbook from the 70s details a number of 11-second build six-pack small blocks (including 273-318!) using factory parts.

Yes, I know Ma Mopar wasn't the first to introduce the six-pack, but they were arguably the most successful at developing and marketing it. The fastest Mopar in the top-50 fastest US musclecars tested in the 60s/70s - and third overall - is the 1969 Road Runner 440 six-pack: https://www.hipforums.com/forum/threads ... le.151109/

So again, I'm not saying it was the best intake ever invented, but credit where it's due.

[F-BIRD'88]

And the more radical the motor build EG: aftermarket heads, roller cam etc the bigger the tri power holley 3x2bbl carbs advantage over a single 4 bbl on the same style intake manifold.
If you put a tri power carb setup on a racing single plane manifold or on a tunnel ram ( with custom plenum carb top) it will eat a single 4 bbl.
All while being more street friendly too.

[b73]

Thread dig!

Only a few years ago you could by a 3x2 SB Mopar intake from Summit for under $400, but they are no longer made

Does anyone happen to have one they bought and would like to sell?
Please PM me if you can help.

https://www.summitracing.com/parts/DCC-4529054

[rebelrouser]

There are a couple on ebay with carbs, kind of expensive. I would look up the A-body forums or other mopar forums and ask around, should be a few left lying around.
https://board.moparts.org/ubbthreads/ubbthreads.php

[b73]

Thank you. I had tried the A body forum but didn't know about the other one.

[Rick!]

I'm also wondering if it's worth running O2 sensors on all 8 cylinders (exhaust) - instead of right/left bank - to compensate for uneven flow. If #1 and #7 are the problem, then a left-bank O2 sensor might be able to compensate. The ECU I'm planning on running will be able to compensate for individual cylinders on a sequential fire basis with up to 8x O2 inputs and 8x injector outputs.

Thanks.

Some dyno shops have headers with individual cylinder bungs. Since a sbm may not be popular down there, you may have to create your own dyno headers.
On the dyno, run 8 heated O2s and dial in the fueling with closed loop and a learn table if the system has the capability.
Trim individual cylinders as needed.
In the car, dual 02s in the collectors is all you'll ever need.
Dial in all the part throttles in the base fuel map and tune TPS_rate of change for the accel pump and run closed loop everywhere.
Avoid leaded race gas.
YMMV.

[Aussie Chrysler]

I realize this is an old comment, but here we go any way... fuel distribution by virtue of having the carburetor’s barrels spread over the length of the engine’s intake ports is superior to having a single carb mounted in the center. Whether or not fuel distribution is actually improved depends on intake manifold design. But, the potential for superior distribution goes to the Tri-Power.

Old thread revive – just in time

Do you think the same applies for EFI in relation to airflow? I will be using direct port sequential injection.

OK, I hate to admit I still haven't installed this set-up. Various reasons, including a few years of remote work while the car was in storage. However, the engine and gearbox are out and the whole car is finally being fully restored, including the EFI installation.

As I never got an answer as to how the six-pack manifold flows from port to port, the only option left is to get it flowed myself. I have an ECU and dual wide-band controller and will be running bank-to-bank injection. A manifold flow test is probably going to be cheaper than time on the dyno, so if I can get the ports to flow as evenly as possible, then I have a set of sacrificial headers I can drill and weld for O2 or EGT bungs which can be used to monitor individual cylinders.

The problem with the six-pack manifold is that at face value it appears #1 and #7 have not only a dog-leg runner to contend with, they are at the ends of the manifold so don't benefit as much from flow from the centre carb/throttle body. Conversely, #3 and #5 have an almost direct line from plenum to port and are also close to the centre carb/TB, so are likely to flow even better, leading to uneven distribution on the left-hand side.

That's the theory anyway and no-one else seems to be able to shed any light on this. I've looked everywhere.

[Aussie Chrysler]

I noticed that you have what appears to be a #6 cross over fuel line between the to fuel rails.Do you think there will be enough fuel volume for the other side of the engine??

the reason I ask is I just finished up a 383 using the holley system and it was lean on the other side.I used a #8 cross over line and the issue went away

I should mention this was a single 4 barrel style base plate not a 6pak set up.

Re-reading this thread some years later, I realise I misunderstood what you meant in regards to running AN8 hose between the AN6 rails. I will see how much room I have to fit a Y front and regulator back (as per solution below), and if not, then I will likely run 8AN between the rails as suggested.

Instead of fuel crossover, it’s better to let the fuel in at the front, via an y, to both banks. Tie together at rear to a regulator.

[panic]

My remarks on my site: http://victorylibrary.com/mopar/weiand.htm

[tjs44]

FWIW,I have been driving-racing multi carb pontiac since 1962.Never found anything better than a good 2-4 intake system.Tom

[tjs44]

Im running a Bathtub tunnel ram on my 62 421 GP,same on my 63 Lemans SD 421.Preparing to put another on my 455 69 Firebird.Have run Tripowers and 2-4s since 1962 with every factory intakes and also the Offy and E 2-4 intakes.Right now running a pair of factory 421 SD NASCAR 750 AFBs.On the other factory 2-4s I ran the 625 factory 421 AFBs.Tom

[tjs44]

The GP

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