The Six-Pack Manifold Thread

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Re: The Six-Pack Manifold Thread

Post by Aussie Chrysler »

Continuing on from the previous post, as long as you have even fuel distribution in a carburetor engine, it doesn't matter so much that some ports flow better than others, because they will all (mostly) get the correct AF ratio. The only real issue is uneven cylinder filling.

The problem with sequential EFI is that you have to feed individual cylinders by setting the injector pulse and then rely on O2 (and other) sensors to trim the fuel to match the desired AF ratio.

As far as I'm aware, this can be done one of two ways: set all 8 injectors pulses the same based on an average AF ratio and then have individual O2 sensors to trim each cylinder; or set each injector pulse individually to match each cylinder, and then use the O2 sensors to trim the average.

The first method requires an O2 sensor for each primary exhaust pipe and an ECU that can process all eight inputs. The second method would require setting the engine up on a dyno and measuring the exhaust from each cylinder whilst setting the individual injector pulses to the required AF ratio, and then letting the ECU trim those pulses based on the average from two O2 sensors (one on each bank of cylinders).

The last - and arguably easiest(!) - method would be to try to even the airflow so that each cylinder has the correct (or ballpark) AF ratio to begin with.
Last edited by Aussie Chrysler on Wed Feb 21, 2018 10:45 pm, edited 1 time in total.
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Re: The Six-Pack Manifold Thread

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turbo2256b wrote: Wed Feb 21, 2018 2:53 pm would start by finding out what your heads flow then bolt on the intake and do a flow test. runners on the intake not being tested must be taped off
Thanks - this makes perfect sense. The individual cylinder only sees what the head - in conjunction with the manifold - flows for a particular port. So it could well be that the best flowing manifold ports are matched to the worst-flowing head ports and vice versa.
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Re: The Six-Pack Manifold Thread

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Powertrip wrote: Wed Feb 21, 2018 4:02 pmYou're not kidding when you say info on 6-Pack manifolds is hard to find. Hughes Engines does a lot of 6-Pack porting, but I am sure they are not willing to share.

I while back there was an article in one of the rags about modifying a Big Block 6-Pack for performance, one of the things they tried was cutting down the dividers, it turned it into a turd on the dyno. I don't know if that would hold true for EFI. I can't for the life of me find that article on line.

I have a complete BB 6-Pack sitting on the shelf, one of my future projects will be full porting, carb mods, and then a direct comparison to a big single combo. I will NOT be cutting down the dividers. :lol:
Yeah, the more I thought about it, the more I came to the realisation that each side-by-side port is open to the other, which would equalise pressure between the two manifold halves (left/right), as each port is fed by a different venturi in dual-plane mode before the secondaries open up.

I did find an interesting write-up here: http://www.bigblockdart.com/forum/showt ... E-SIX-PACK

The gist of this post is that - at least on the carby six-pack - you should block off the outboard venturis to fine-tune the centre carb first, then seal any vacuum leaks from the outboards before tuning the rest of the engine. Apparently the outboard carbs leak a lot of air even when closed, which interferes with the central carb metering at idle and part throttle. This is why the outboards also have an idle circuit. The idea is to eliminate the outboard idle circuits and seal the venturis so that engine can only draw air/fuel from the central carb at idle/part-throttle, making it much easier to tune and realising the manifold's full dual-plane potential (with no air leaks or fuel/air interference downstream from the outboard carbs).

I hope that all makes sense :-?
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Re: The Six-Pack Manifold Thread

Post by F-BIRD'88 »

Yes those are cross rams that already exist. I am suggeting a tunnel ram SB mopar manifold that already exists, but changing the upper plenum on it to use the 3 carbs or 3 EFI throttle bodies.
Getting the cylinders to flow the same and getting he AFR's the same will be a lot easier with the tunnel ram over a cross ram. You can also play with the tunnel ram runner lengths by adding runner spacers between the bottom and custom 3x2 plenum top sections for effect...
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Re: The Six-Pack Manifold Thread

Post by Geoff2 »

So why were six pack intakes 'invented'? Only two reasons that I can see:

[1] There were no single 4bbl carbs large enough to flow enough air
[2] They look great & sell cars...

The problem that I see with the inline design 6 pack is one of equal distribution. Example. The rear carb sits over the rear 2 cyls. Very short runner from THAT carb to the 2 rear cyls. This carb is jetted to provide the correct F/A mixture to the rear cyls. But what happens when it is time for the front cyls to draw air? Mixture from the rear carb will now be lean because of the long runner length.
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Re: The Six-Pack Manifold Thread

Post by turbo2256b »

first would make sure each port in the head flows the same.
as for the right side and the left side ports of the intake needing different porting has more to do with push rod location.
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Re: The Six-Pack Manifold Thread

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Geoff2 wrote: Thu Feb 22, 2018 4:35 am So why were six pack intakes 'invented'? Only two reasons that I can see:

[1] There were no single 4bbl carbs large enough to flow enough air
[2] They look great & sell cars...

The problem that I see with the inline design 6 pack is one of equal distribution. Example. The rear carb sits over the rear 2 cyls. Very short runner from THAT carb to the 2 rear cyls. This carb is jetted to provide the correct F/A mixture to the rear cyls. But what happens when it is time for the front cyls to draw air? Mixture from the rear carb will now be lean because of the long runner length.
You must have never taken a ride in a 1965 GTO with Tri-Power!
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Re: The Six-Pack Manifold Thread

Post by Geoff2 »

Er,
I have been for a ride in a 66 GTO with Tri Power, which has a larger centre carb than the 65 Tri power.

There is NO getting away from the fact that F/A distribution of 6 bbls feeding 8 cyls is going to be worse than a single 4 bbl that is centrally located on a well designed 4 bbl intake manifold.
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Re: The Six-Pack Manifold Thread

Post by 427dart »

The reasons for the Tri Power was yes back in the day 3 2bbl. carbs offered a bit more total flow than the current single 4 bbl.
Plus the setup offered the economy of the single 2bbl. when cruising and for performance image and sound it was VERY COOL!
These setups in cases like Pontiac often cam with a hotter cam as well.

We weren't thinking about ultimate fuel distribution back then....we just knew it was faster than the base single carb setup!
I must mention some of the 3x2 setups were troublesome like the Chevy 427 and Chrysler 440 triple Holley 2bbl setup where getting the vacuum actuation to function correctly. I believe the Pontiac system worked much smoother.
When I was 11 yrs. old summer of 1965 a neighbor had just bought a new '65 GTO with Tri-Power and it was a wild ride and left me with a big impression!
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Re: The Six-Pack Manifold Thread

Post by pdq67 »

I would love to have the Weiand 3x2 intake above, but for a SBC!

I would think that the long cross runners would make great torque...

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Re: The Six-Pack Manifold Thread

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Geoff2 wrote: Fri Feb 23, 2018 4:42 am Er,
I have been for a ride in a 66 GTO with Tri Power, which has a larger centre carb than the 65 Tri power.

There is NO getting away from the fact that F/A distribution of 6 bbls feeding 8 cyls is going to be worse than a single 4 bbl that is centrally located on a well designed 4 bbl intake manifold.
Be that as it may, there's more than one dyno comparison out there showing Mopar six-packs making equal or more power than 4bbl combos on the same engine. Even if you argue some of the comparisons put more time into tuning the six-pack than the 4bbl set-ups, it's proof they make power. I think it was Hughes who said he likes six-packs because "they make more power than they rightfully should!".

I'm not trying to gild the lily, but Chrysler did a pretty good job (in its day) of designing an induction that combined dual-plane driveability and economy with single-plane type top-end flow. It may be a 50-year-old design, but the dyno figures don't lie:

http://www.hughesengines.com/TechArticl ... 012007.php

http://www.hotrod.com/articles/mopp-021 ... stem-test/
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Re: The Six-Pack Manifold Thread

Post by Geoff2 »

Aussie,
Quite agree with you about Chrysler six pack engines. Whether 340, 440 or the Aussie 265, they performed.

However, before you sing the praises of the 340/440 six pack engines, you need to look a bit closer. I will use the 440 as an example, the 6 pack was rated at 390 hp, the 4bbl engine at 375 hp. Both engines used the same cam, same heads & pistons, same Hi Po exh manifolds. So the 15 hp difference was in the induction system.

The 6 pack intake manifold was a true high rise manifold, with sweeping bends in the ports for good flow with minimal restriction. By contrast, the 4bbl manifold was very poorly designed, one of the few times that Chrysler stuffed up. Manifold was low slung, with tight bends, small plenum & restrictive. If the the 4bbl manifold had been better designed, I think the 15 hp difference might have disappeared...
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Re: The Six-Pack Manifold Thread

Post by Aussie Chrysler »

I'm not going to argue the six-pack is something isn't. But fact the old 4bbl factory manifolds can't keep up with newer designs just proves how far ahead of their time the Mopar 3x2 manifolds were. Here's a Victor 440 making almost 25hp more than a six-pack: http://www.hughesengines.com/TechArticl ... st7279.php

Except on a 645hp engine, that's less than 4%. The six-pack also makes an average 13hp more than the Victor across the entire rev range and kills it on bottom end and mid-range up to 4300rpm. I know what would work better on the street . . . though you could argue something like an Air Gap would work even better (maybe).

I think we all know that advertised horsepower figures were grossly underated in the 70s by all manufacturers for insurance (and possibly media "super-car scare") reasons, and that the 4bbl 440 made closer to 410hp while the six-pack made closer to 430hp: http://www.ultimatecarpage.com/forum/sh ... hp?t=33343

So to be fair, when builders say you can make better horsepower or torque with modern manifold designs, they're not wrong . . . but they're not right by much either!

Let's just agree that it was a good design for its time and is still none-too-shabby even in the modern era.
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Re: The Six-Pack Manifold Thread

Post by turbo2256b »

my first engine build back in 66 67 was a 312 Y block police interceptor dual quad. it kicked but after some rework isky cam some port work ,carb jetting. installed in my dads 56 ford
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Re: The Six-Pack Manifold Thread

Post by Powertrip »

Aussie Chrysler wrote: Wed Feb 21, 2018 11:30 pm
The gist of this post is that - at least on the carby six-pack - you should block off the outboard venturis to fine-tune the centre carb first, then seal any vacuum leaks from the outboards before tuning the rest of the engine. Apparently the outboard carbs leak a lot of air even when closed, which interferes with the central carb metering at idle and part throttle. This is why the outboards also have an idle circuit. The idea is to eliminate the outboard idle circuits and seal the venturis so that engine can only draw air/fuel from the central carb at idle/part-throttle, making it much easier to tune and realising the manifold's full dual-plane potential (with no air leaks or fuel/air interference downstream from the outboard carbs).

I hope that all makes sense :-?
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.
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