[Zeemax]

Part of the Grassroots Motorsports article on the Protege/EscortGT caught my eye. According to David Avard, "most of the intakes sacrifice torque...besides the stock VAF is restrictive enough to limit anything you might do with intake piping."

My question then is whether there´d be any benefit to going with a slightly smaller diameter than stock for the intake pipe. Keeping the stock VAF, but a 1/4" less sized pipe might yield greater airflow speed, better filling of cylinders, etc. Don´t know if there´d be any measurable horsepower reduction at high rpms. Has anyone tried using a smaller diameter pipe in order to maximize torque over horsepower? Or anyone want to discuss the merits of such an effort?

 

[birddog]

This would be an interesting test to do. If I get the time this year, I may try to get some runs at the strip with some different sizes. there would have to be some real gains in low end torque to justify giving up any of the high end hp. now you have me curious!

 

[siragan]

Great idea, but what about the TB...

and yes, the VAF is restrictive as all hell.

 

[TheBlade]

After everything I´ve done to my car I´ve come to the conclusion the more pressure I run...the more power I get :-D Sorry guess that doesn´t help anybody...but boost is fun.

 

[92gt5spd]

alright, yeh, i hate the vaf too. I adapted a new system. See, that little valve on the inside of the vaf.. air pushes it open right? Well, i took an old tb and attached the rod going throught that to the tb and had it so that it would spin the same when air pushed the tb open. i scrapped the project, cuz i got bored, but who knows, someone might try working on it again.

 

[Pimp_scort_89_GT]

I wonder what relation ship the VAF signal and TPS signal have to each other. If they rise at the same rate you could essentially wire the VAF wires to the TPS and forgo the whole intake system.

 

[TheBlade]

actually the best thing to use is a MAP sensor. then all you need is a filter and that´s it. calculating manifold pressure will account for temperature, air density, all aspects of sensors for air flow/fuel calculation.

Problem is you need an ECU designed to use manifold absolute pressure....like a Haltech.

 

[Zeemax]

When using a smaller diameter pipe, at the same engine rpm, the intake air would have to be moving faster through the pipe, that´s just physics. But the speed effect would be negated when the diameter increases at the TB and then into the intake manifold. I suppose that only somebody like Blade running turbo would notice the effect of a smaller diameter pipe, since he´s pushing more air through a smaller pipe, intake velocity would be even greater, resulting in increased cylinder filling during the intake stroke... It´s all theory, but hell, it might make a difference?

 

[TheBlade]

yeah, I lived with a guy that had a turbo´d civic. He ran like 2.5" IC piping. The piping was WAY too big, so he had horrible turbolag and in-efficient boost.

After seeing that happen to him, I chose to go for 2" piping. The 2" piping seems kinda big for 5psi or so, but I think it will be needed when I go for 12-15psi.