Custom Intake Manifold

[2.8/3400 1985 Camaro]

Well long runners aren't necessarily bad, I can never remember which gives more torque and which gives more hp, but I'm wanting to say that longer runners give more torque, while shorter runners and more plenum volume give more top end power. Headers have the same effect, but once again, can't remember if longer is more torque or shorter is....but I think its longer=more torque.

[ericjon262]

yeah, but long bent up runners are no good...

[2.8/3400 1985 Camaro]

If there's two things I never got about the 60/6 its that GM gave all the love to the fwd cars when all they had to do was change the pistons to a lower dish to give the RWD cars a much needed performance boost, esp considering firebirds and camaros are GMs 2nd notch in the performance sector after the corvette.....the other being the 3.4 intake design.....they could have made it so much better...it would actually be relatively easy to adapt the 3.4 rwd UIM to a dual TB setup, and give it more volume, I would probably do it if I weren't planning to go hybrid.

[TiredGXP]

Once upon a time I saw some flowbench numbers for the gen 1 head with and without the stock intake manifold attached. IIRC, the intake is a significant restriction on overall flow. The neck on the intake is significantly smaller than the 52mm throttle body, and the u-turn bewtween the top and mid sections of the intake both hurt flow.

I have plans for a divided (but siamesed) plenum set-up to replace the upper and mid intake sections for my Gen 1 3.2 . This will be fed by a dual 48mm LT1 throttle body, Total plenum volume of nearly 5 liters and an intake runner length of 14.5 inches from back of the intake valve. The large plenum is because this is a turbo application.

Wish I had solidworks, or something equivalent, to create a 3D model.

[Superdave]

in general longer runners give more overall torque with peak HP lower in the RPM range, shorter runners are the opposite. Hilborn injection works the same way with the different length ram tubes but in that setup it's all adjustable. That's for a N/A engine..

[TiredGXP]

Agreed.

Not too worried about long runners for low RPM operation in my application - the turbo will take care of generating torque as it spools up, I'd be designing a bit differently for a n/a application.

Just an aside, 2000-4000 rpm in my Subaru is a rush - starts boosting at 2000, with 16psi by 3000, but the turbo can't hold full boost much past 4500. Drops to 11 psi at 7000.

[trotterlg]

Anyone ever tried this? Machine a pad on the top of the upper intake manifold, cut a couple of holes in it to match up with a 2 barrel carb. Run the carb totally closed until you run out of TB opening, then start opening up the carb, sort of like flipping the switch on a Nitrous system. Upper intakes are dirt cheap and so are 2 barrel carbs. Larry

[robertisaar]

that would essentially be adding mechanical secondaries to a MPFI setup... LOL

[trotterlg]

Make a good science experment.

[pocket-rocket]

Are you going to run a dual MAF so you don't throw the computer way out of whack?

[robertisaar]

Are you going to run a dual MAF so you don't throw the computer way out of whack?

dual MAFs wouldn't be required, so long as the MAF measures the combined flow of all intake sources... like this:




the box on the left is your air filter, the black band is the MAF, and then the tube splits into two sections for each TB/carb...

[pocket-rocket]

Well, then there's the custom hole in the hood mod you would need for the TB and the tubing, but if you are going to go through all that, you may as well throw an M90 on it like Dave with the Monte did.

[robertisaar]

mah arts is teh greetest!

[pocket-rocket]

Except that your upper TB tube is almost pinched shut, yeah, lol.

[robertisaar]

well, all concepts have flaws... a 2 barrel carb can't draw that much beyond what a fully opened TB can do anyway.