YEa Isent the stock exhaust tubing 2.5''

 

ok a bigger exhaust will almost always help a turbo, a stock 2.5 exhaust will def hold back your potential, 3inch is usually best even if your not going to run a big turbo as you dont need any more back pressure since thats what the turbo creates

 

A larger diameter pipe will cool down exhaust gases much faster than a smaller diameter pipe. Cooler gases mean a slower exhaust velocity. You're speaking of exhaust velocity, not backpressure. A turbo running a small to moderate amount of boost can use the stock piping and give no regard to "holding back potential".

99% of backpressure happens between the primary pipe/turbine area and the valves...before the exhaust piping. A turbocharger creates more backpressure because of its turbine in the path of said primary pipe. Whether you have 2.5" exhaust piping or 16" exhaust piping, backpressure in that area would still be the same.

There is no accurate way to calculate what pipe diameter would be optimal for a particular after-market setup...there are too many variables. Many people claim they can, but ultimately, they cannot. Anybody who says otherwise is trying to sell you something. But, a widely known rule of thumb is 3" - 4" for 250 - 350 BHP. Putting 3" piping on the '08 would be a waste of money, time and effort. Get a high flow cat, keep the stock piping, ditch the muffler and there's your turbo exhaust setup. Keep it simple. As a real life reference, Garrett recommends 2.5" for up to 250 BHP.

You do want high exhaust velocity with a turbo setup, no doubt (high-flow cat, less restrictive or no muffler). But, an unnecessarily large pipe diameter will produce diminishing, or more likely, no returns, I promise. The most important aspect of a turbo setup is your primary pipe on the exhaust header...if the diameter of that is too large, the turbo takes eons to spool. As another real life reference, I'll use myself: I kept stock piping on my GVR4 while a friend of mine went 1" larger on his. We are both skilled drivers. His car would fall flat on its face noticeably sooner than mine.

I'm sorry to disappoint...but bigger isn't always better and stock isn't always bad. That XYZ brand exhaust looks awfully good with its giant piping, but it's ultimately worthless. And I KNOW...I just KNOW I will be accused of this post being wrong because it rubs against almost all popular knowledge about exhaust systems. Once again, I hate to disappoint...but I'm right

 

^ to true on the you dont know nothing because my ________ (fill in the blank) said that 4'' pipe is the best what you only have 3'' ooo that's holding you back.

 

lol showtime whats up dude your back now I see

 

but i think with this turbo kit you will be over 250bhp, so that would mean 3 inch like i said, no?

 

If it's over 250, then yes, 3" would be OK. But your original logic as to why was incorrect, hence my rant

 

but i think with this turbo kit you will be over 250bhp, so that would mean 3 inch like i said, no?:

But don't forget that our cars are dynoing in the high 120's/low 130's, so even with a 100 HP turbo, you would fall short of an exhaust upgrade.

 

lol ok enough bickering with us, lets agree, if most go over 250, you would want a 3, thats what i thought we would easily accomplish, agreed lol

 

250 sounds nice...

 

250 does sound nice but based on most of the previous posts, you're probably going to be looking around high 100's at the wheels with low 200's at the crank, but that all depends on how much boost the turbo and tranny will be able to handle.

 

I would like 250 but I do remeber Rob saying it may be 280 I could be wront tho, 3 inch is the way to go....

 

It's well known that the whp from the factory is about 130. The turbo kit from RRM has supposedly 7 lbs. of boost. I also hear that as a general rule for every pound of boost the turbo provides is good for a 10% increase in power.

130whp X 10% = 13whp
13whp X 7 LBS. = 91whp
91whp + 130whp = 221whp

Even with a high-flow cat and other stuff like crank pully I'm guessing the car will still be under 250whp.

 

Ideally, yes you get 10% for every pound of boost, but this isn't an ideal world and a more realistic figure is around 6-8% so figure

130whp X 7% = 9.1whp
9.1whp X 7 lbs = 63.7whp
63.7 + 130whp = 193.7whp

The results may be a bit better but I, personally, would rather be surprised by a dyno giving me higher whp rating than a lower dissapointing number. Even if you average mine and ProRCRacer's numbers you'll probably see around a total of around 200-210whp, depending on how efficent the turbo actually runs.

 

OT: WOW! huge jump in drivers from IL

we should all meet up some time!