subaru wrx VNT

a friend of mine has an 04 subaru wrx. although he got 14.8 out of it at the strip, it feels like theres plenty of room for improvement in the power delivery. when you go for a ride in the car you immediately notice poor throttle response, and feel hard acceleration only between 4,000 and 5,400 rpms where power drops off slightly. When i thought about the problem for a while and came to this conclusion... most 4cylinder cars are in straight/inline 4 layout, the subaru however is a boxer engine. The turbo on any inline 4cyl is usually no more than 15" away from the exhaust ports on the cyl head. on the boxer motor due to the two separate heads placed at opposite ends of the crank the turbo has to wait for the exhaust manifolds from both sides to come together, placing it much further away from the ports... based on my limited knowledge of turbos, i would think that this dramatically increases lag and causes the delay in response and power?? MY QUESTION: the garret VNT was designed to dramatically reduce lag and improve throttle response, and was supposed to be dependable to 14psi. although the vnt reduced top gear acceleration, it didnt effect 1/4 mile times of the 2.2's it was mounted on. the wrx runs 12psi max right now, can anybody tell me what they think would happen if we put a VNT on the wrx's boxer engine at 12psi

[contraption22]

WRX's respond extremely well to exhaust upgrades. Especially when you remove the 3 cat converters they have.
He is lucky in that the WRX is a popular vehicle, and he can very easily just pic a tried and true buildup formula and go with it. No sense in re-engineering the wheel with '80's technology.

i guess this isn't the place to ask that question is it...

[contraption22]

Quote:

Originally Posted by Ominous i guess this isn't the place to ask that question is it...

I moved the thread to the appropriate forum.

[cybermrc]

Sure it is!
If you remove any exhaust restrictions, you will notice increased throttle response, faster spool, and faster spool at lower RPMs.

3 catalytic converters is a huge exhaust restriction.

[Kryp2nitE]

well how mechanically inclined is he?

im new to turbos but i would guess that the mounting pattern wont b the same, the cooling lines will have to be re routed how is boost controled on the WRX by the comp or some stand alone system?

you would probably need a custom computer, new lines new intake plumbing

do they make really small turbos? could he run twins?

it would be nice to just go with an exhaust upgrade or remove the cats but on a subaru a good exhaust system will easily set you back $1000, especially if you want to make sure theres no boost creep i guess...in an article i read in an import tuner? magazine when testing a full exhaust they put a boost controller on the car afterward and set it to 12psi, where they discovered that their real power gain was only a few hp, around 5 at the wheels if i remember correctly. i think they spent around $2000

i think twins would cause more plumbing problems and since i would be the one working on the car i dont think installing different oil/coolant lines on the vnt would be a big deal, aside from some different fittings. fabricating a mount plate wont be too bad ive already done it once. boost is controlled by the computer, but if a boost controller was set at 12psi i dont think the computer would have a problem would it?

p.s. its funny how the dodge forum is more helpfulthan the wrx forums

[The Barron]

Quote:

Originally Posted by Ominous p.s. its funny how the dodge forum is more helpfulthan the wrx forums

Probably cause most of the O\/\/nerZ probably dont even know how to change the OIL!

[Dan Culkin]

Sounds like the WRX motor flows comparably to a T3 engine (220ish hp@12psi for the wrx, 224@11psi for the T3).

A single VNT would be a poor match for that motor.

[Kryp2nitE]

lets not get too hasty here

do you have the specs on the stock turbo? wheel size and stuff
if we compare the specs of this turbo to stock TD's maybe we can find a better match

the problem with the VNT as you alreayd know if that it must spin several times more to make the same boost


are you serious about the cost for exhaust? holy crap even if you go to a shop and have them bend new pipes? how about side exit?

[contraption22]

Yeah the exhaust is expensive.. but certainly less of a headache than re-engineering the turbocharger system would be. and a freeflowing exhaust should ALWAYS be the first step in upgrading a turbo car.

[Phreakish]

I gotta chime in here - a little longer exhaust manifold, or longer turbo plumbing will make almost NO difference in lag. The true lag comes from the ability of the engine to spool the turbo. When you step on the gas, you dont immediately get more flow from the engine - after a little bit, the engine flows a little more, which spools the turbo, which flows a little more, and voila; boost. Pressure is pressure - ever try to time how long it takes an exhaust pulse to get from the cylinder to your tail pipe? Not long. And as for long hoses to intercoolers and such, it doesn't take long to fill that amount of volume, so long as there is no large restriction, there's no problem.

Drop the exhaust as an experiment and see what happens, try a grainger and see if the car complains (I've read that some newer cars dont like to be grainger'd, but who knows).

After trying those (to rule out their involvement), THEN I'd move onto the turbos and such. Its much cheaper to buy a hacksaw blade and an exhaust coupler than modify an exhaust manifold and plumb in a new turbo

ok i guess we'll have to check out some low cost exhaust options, thanks for the help and explanation fellas

[aenimacs]

Correct me if I'm wrong, but don't they (WRXs) have a cat before the turbo.