3x2 intake build.

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pdq67
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3x2 intake build.

Post by pdq67 »

I think that somebody tried to or did make a 3x2 intake that used a whole Q-Jet as the rear carb. and only the big rear barrels for the front carb!

Like this O o O
...........O o O

Anybody know how this worked out?

Kinda like a Pontiac GTO 3x2 intake that used a little Rochester 2G carb for the middle one and the bigger Rochester 2GC carb's for each end.

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Re: 3x2 intake build.

Post by superpursuit »

I think what you are referring to was posted by "F-Bird'88". You may want to PM him for more details.
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Re: 3x2 intake build.

Post by lefty o »

thus far, i believe its a fantasy piece. essentially what you show is a basic mopar six pack manifold, 350cfm in the center with 500's for the outboard.
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Re: 3x2 intake build.

Post by pdq67 »

superpursuit wrote: Fri Apr 12, 2019 10:40 pm I think what you are referring to was posted by "F-Bird'88". You may want to PM him for more details.
hey, F-Bird88, are you still here?

If this was you, then how did it turn out?

Sounds like a great idea if both 750 cfm Q-Jets are mechanically connected for tip in...

And if they aren't enough cfm, then use two 1,000 cfm T-Quads!

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Re: 3x2 intake build.

Post by chevyfreak »

From what i remember it was fbird that posted about it.


I could be mistaken but from what i know the mopar sixpac all barrels worked together and the gm tri power were progressive setup and only ran as a 2 bbl and 6 bbl at wot.
Am i mistaken or not?

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Re: 3x2 intake build.

Post by F-BIRD'88 »

Yes it was me. No I have not built it yet.
But it is on the list.
Did you have any questions?
This is somethibg that anyone can do.
A lot of different ways you coukd use it too.

It will be relativly simple to modify the front carb
To disable the primary side so it is a (secondary carb only) yet the throttle action and linkage is simple.
Have not decided wether the front primary accelerator pump should be kept active, with a modified discharge path into the plenum. The front carb primary throttle is not exposed to the plenum.

The total cfm if/when at WOT and if both secondary air doors are wide open the cfm capacity would be some 1290 cfm @ 1.5". Of course that is fully adjustable and progressive by nature of the (2) secondary air doors design.
You also gain the benefit of having 2x fuel inlets, 2x fuel bowls, and can be 2 accelerator pumps or 1.
Bigger fuel metering capacity for high output engines.

Yes the front and rear carbs throttle connection is a simple rod link. But the 4 secondaries are progressive by the action of the QJet throttle linkage action.
It idles and drives around on just the 2 primary barrels, which are now (very near) in the center of the manifold plenum say on a 4 bbl intake manifold.
On the front carb the lower half of the primary throttle blades is removed. The primary metering rods are removed. The primary main jets are blocked. The primary idle fuel feed passages are blocked. The primary side is not used. But other than cutting off the lower half of the primary throttle blades all the linkage is intact.
On the under side the lil passages between the primary and secondarys on the base are blocked.
Last edited by F-BIRD'88 on Sat Apr 13, 2019 5:24 am, edited 4 times in total.
F-BIRD'88
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Re: 3x2 intake build.

Post by F-BIRD'88 »

Yup the Thermoquads would be candidates for this too.
The early QJets pre 1975 "4mV" can be mounted relativly close together, in line and also if back to back.
This scheme is inline, useing 6 of the 8 venturi , of the 2 q-jets.
No rules...;-)
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Re: 3x2 intake build.

Post by mag2555 »

You guys must have a lot of time on your hands for such a project?
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Re: 3x2 intake build.

Post by lefty o »

chevyfreak wrote: Sat Apr 13, 2019 4:00 am From what i remember it was fbird that posted about it.


I could be mistaken but from what i know the mopar sixpac all barrels worked together and the gm tri power were progressive setup and only ran as a 2 bbl and 6 bbl at wot.
Am i mistaken or not?

Chevyfreak.
on the mopar, the outboard carbs are vac.
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Re: 3x2 intake build.

Post by chevyfreak »

lefty o wrote: Sat Apr 13, 2019 8:59 am
chevyfreak wrote: Sat Apr 13, 2019 4:00 am From what i remember it was fbird that posted about it.


I could be mistaken but from what i know the mopar sixpac all barrels worked together and the gm tri power were progressive setup and only ran as a 2 bbl and 6 bbl at wot.
Am i mistaken or not?

Chevyfreak.
on the mopar, the outboard carbs are vac.
Thanks for the correction.

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Re: 3x2 intake build.

Post by F-BIRD'88 »

mag2555 wrote: Sat Apr 13, 2019 6:58 am You guys must have a lot of time on your hands for such a project?
It's those long cold Canadian winters, maybe the high octane Canadian beer too..;-)
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Re: 3x2 intake build.

Post by falcongeorge »

I understand the creative urge, but if you want to run 3x2's on a sbc, just get a 4 bolt 357-B and run 3 rochesters. Its a surprisingly stout intake, I saw a magazine dyno test where it beat a performer RPM and AFB on a 350ish hp 307 by a solid 10hp and 5-7 ft lbs, and that was with 3 bolt strombergs. The rochesters will pick up power over the strombergs. Don't be fooled by the fact that its a 60 yr old design, its a pretty good piece. I think guys overlook it as a legit performance induction for street small blocks in the 400-450hp range, and with 3 rochesters and progressive linkage, I bet it would surprise you in terms of part throttle economy and streetability as well.
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Re: 3x2 intake build.

Post by SchmidtMotorWorks »

Any regular 3x2 manifold has too short of runner length.
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Re: 3x2 intake build.

Post by F-BIRD'88 »

A Edelbrock Dual Quad Perf RPM air gap hi rise Dual plane manifold can be modified to accept 3x2 holley carbs..
Reqjires cutting the 2x4 carb flange tops off it and fitting a bolt on custom plenum top. Could then be 3x2 or 1 x4 + 1x2 carbs. Or could be 3x2 rochesters.. or 2x4 holleys on spacer adapter. The taller the custom bolt on divided adapter plenum top, the better. . Still same or shorter carb height than most racing single planes..
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Re: 3x2 intake build.

Post by F-BIRD'88 »

A taller 3x2 intake manifold allows longer tuned runners of equal or near equal length. Like a Tunnel Ram.
Further: any good powerfull single 4 bbl intake manifold should work very very well with a proper height/plenum contour 3x2 carb to single 4 bbl adapter. Its going to add about 3" carb height for a good transition, all said and done.
May not have mass market appeal but will have a few advantages over a single 4bbl carb. Including making a bit more power when on a hungry high output engine.
Now you got a reason to run a hood scoop and or actually need a aftermarket cowl induction hood.
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