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Intake design and sizes

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91-GS

Proven Member
1,390
65
Jan 12, 2013
Paris, Tennessee
Not sure if N/A and turbo intakes are different, but for this discussion set's assume that we are building a N/A car that will compete in time trial races. That means that we have to maximize performance throughout the RPM range.
Some time ago i had in idea for a manifold that was built similar to a equal-length exhaust header and in such a way that air gradually turns from throttle body into the runners and into the engine. In that configuration air does not have to make that sharp 90 degree turn into runners as with standard design. (see design here)

Are there any other possibilities other than stock?
And what would be a good way to make them adjustable on-the-go so to produce best results throughout the RPM range?
And what about everything that is before the throttle body? It it important, or does it not matter as long as the air is clean and measured?

*Please note that this thread goes together with this exhaust system discussion thread
 
ITB.

or, take the time and $$$ to build a tuned intake. Takes the intake pulse (when the valve closes the air bounces back off the valve into the intake, then bounces back toward the valve) and tune the pipe to the exact moment the pulse makes it back to the intake valve when it opens. It "forces" the air in... exact length and size all depend on when you want this phenomenon to happen in the rpm range.
 
Been looking at online calculators and found out that for low-end torque on 4G63 the runners need to be 12" long and have a 2" cross-section (that is exactly what stock 1G is). On one hand it sounds simple: take correctly sized pipes and weld them together into a manifold. But there is that feeling that it can not be that simple, especially after reading replies in the exhaust thread.
 
Take a look at a stock 3g 4g64 intake manifold. Looks like an aftermarket v8 header. Perfect for an engine that will never see over positive manifold pressure. Not good for a boosted engine in the case that one or more cylinders may get less airflow per intake stroke over positive pressure, causing a power imbalanced engine
 
No, it's not a V6, it's an inline 4.

The multi tube "intake header" design ins't really ideal. It's very complex, doesn't offer flow gains, and is mostly so you can put very long runners into a smaller space to improve low end performance.

There are two areas to be improved upon when comparing the stock manifold, flow and power band. Flow comes from having things like velocity stacks, smooth, tapered runners, and plenum design. Power band comes from runner length and shape, and also from the plenum size. You can spend a lot of time designing these things and not get a lot of gains over a basic manifold.

2.0L NT engines make power with revs. There's not really any way to get more torque out of the engine, so you'll want to design it to gain power up top without sacrificing a lot of low end. Increasing overall flow is really the only way to gain power over the whole rpm range. I haven't spent a lot of time with 4g63 stuff on a flow bench, but it doesn't seem that there is a ton of flow to be had over the stock manifold.

You're then left with camshafts and changing the RPM range the power is made. Slightly shorter runners with a larger plenum will probably go well with larger camshafts and make it rev happy.

You can get resonance tuning in the intake tube, but the effect is minimal. It would be more beneficial to switch to speed density to get rid of the mass air flow restriction. It might be a fraction of a hp, but when you don't have boost you need every little bit you can get.

Oh yeah, making sure you get cold air is important too. Using fast acting temperature sensors you can find where you're getting the coldest, densest air possible.
 
I would think making a modular setup would be ideal to start with. Something like what the RWD 4g63 guys have been doing with the cut & flip on the runners. That would allow you to adjust the length of the runners. You could also make the plenum detachable, and sleeve the runners to vary the ID. Even with ITB's, you will have a LOT of guess and check tuning, and what you think you want may not pan out in on-vehicle testing.
 
Even with ITBs, the best route is to configure a well designed box for them that gets air directed from the front of the car. Help get some positive pressure to the engine.
 
Cut the runners and flip the plenum of the manifold, realign the runners and weld.
 
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