i have a 2001 gsr. im running the skunk2 pro series manifold. to my knowledge, i would have to buy the ls/rs kit so that the charge pipe fits correctly? is this the only difference between the ls/rs and gsr kit?

 

Mainly, yes. But getting an intake manifold for a greddy kit will not net you any more power, if that is what you're trying to obtain. Stay with stock.

 

The downpipe lenght is different between the ls and the gsr, so you will have to get it shortened for a gsr if you get the ls kit.

 

I'd have to disagree with Shodan. The larger IM and the longer runners will flow alot more effiecient than the stock. I would open the IM inlet to about 68mm and throw a larger throttlebody on it. With more volume to flow through, the more effiecient the turbo will spin and with a proper sized exhaust and tune the more hp you will achieve. By the way I'd ditch the stock elbow and dp that it comes with and get a larger custom downpipe built. Believe me you won't regret it.

 

Just get the GSR kit, the charge pipes will fit just fine.

 

with a stock greddy kit it wont be able to flow enough to where changing the IM will make much of a difference (i doubt even a 5hp gain). if your going to get an intercooler then it wont make much of a difference which kit you get. i have a greddy kit with an intercooler, its worked and hooked up perfectly to a LS, b20, and a GSR motor.
if you wnat more power (or even enough power to where changing the IM will make a difference) you need to change the elbow/DP on the greddy kit. also doesnt hurt to change the actuator and to slightly port the inside of the internal WG so it can open and close fully

 

Can anyone elaborate as to why this would be true? At what point/horsepower is the stock GSR manifold restricting power? I'm not doubting the statement, just curious.

 

on an NA set up the force driving the air into the motor is the vacuum created by the pistons inside the pistons. while it does take less force to pull than to push, there is considerably less pressure created by the vacuum than there would be by a turbo. but more importantly is the density of the air.
aftermarket IMs are designed to restrict airflow less than the stock ones, but looking at the general equation for aerodynamic drag (resistance): drag= 1/2 Density x Area x coefficient of friction x Velocity^2. the biggest contributor to drag is the velocity of the object (sinec the object is still in this case, the velocity of the air moving through it) and the smallest effect is the density of the air. so in theory the gains of an IM would be exponential, not linear based off of the amount of air (density speed and L/s) being pulled through. so while a turbo that compresses it to 3x density and pushes it at 10 m/s into an engine that eats 1 L/s of air per second would see some gains, a turbo that compresses it 5x, pushes it at 10 m/s into an engine that eats the same amount would see a MUCH larger increase in HP by switching to a IM with less resistance. as for when your IM is tapped out to its potential: when flow and resistance are equal to each other.

to more directly answer the question: a stock IM will always restrict more power than an aftermarket one, but the point that it restricts it is rather small. the T28 is not a very powerful turbo, so going off the fact taht gains are exponential, not linear: it would be a small gain to upgrade. you would definately free up a few more HP, but not a lot. controversly, on an NA build an aftermarket IM normally gives a pretty good increase in power (despite the fact that gains are exponential), because of the lower density and velocity of air.