hey whats up im planning on getting my exhaust redone since the car is turboed and running good now, right now i have 2 1/4, but i am thinking about going either 2 1/2 or 3 in, someone told me 3 in is a must for a turbo car, but im wondering if that would be overkill, my downpipe is 1/2 in then they put a flex pipe in and then it goes down to 2 1/4 after the cat, so im wondering should i just change the pipe after the cat and make it 2 1/2. right now i am running 10psi daily, also the reason i am doing the exhaust is because the guy who did it originally did a really crappy job and im tired of looking at it like that, i have dual exhaust on there now
if it can't win a race it better win a show
your exhaust is only as big as your smallest size.
for example, if you have 3" pipe and a 2.5" downpipe. its only going to give you the gains for a 2.5" system.
im running 2.5" turbo back and im fine with it, people say i need 3, but i dont need anything. i like it how it is.
but do u think ur setup would benefit from going to 3 in, im just trying to do it right the first time
if it can't win a race it better win a show
depends on your power level and psi and what not. once i get the built motor in, i might go up to 3".
3"
You wont regret it. Better to do it the first time instead of wanting to upgrade later anyway.
but im concerned about the car having no lower end power or not running right before the turbo begins to spools, i dont pretend to know it all about boost so forgive me if this seems a little noobish lol, i just want to do whatever is gonna be the most effective for the turbo setup, im only running 10-12 psi but 10 daily
if it can't win a race it better win a show
Hi!
Here's what we've learned:
We usually consider 300-350 HP to mandate the 3". Anything below that, 3" has no real advantage. A good example is the new Cobalt TC, whose stock 2.5" exhaust is perfect at power levels of 260-300 HP.
As you mention, in certain instances, 3" can also reduce low-speed torque from lower system velocity as compared to 2.5".
Yep...also keep in mind your current and future desires. Don't worry about losing power to a 2.5" under 300 HP". 2.5" is optimal there, so long as well-designed...I'm only vouching for expert-engineered known name brands that can be depended upon to work well.
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com
ok thanks, it sounds like the best bet for me would be to go with the 2 1/2, i am planning on EVENTUALLY building my other motor to make sure it can really handle a lot more hp but that may not be for another year or so so i think for now i will go with the 2.5 in ....thanks guys
if it can't win a race it better win a show
You'll like it better, especially if you value low and midrange torque.
Some guys could not care less about anything other than WOT...and for them, the 3" might be the right choice, especially if they know they will upgrade to big power soon.
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com
other nice thing would be adding a cut out , when you wanna play at the track , that way you can keep the nice around town driveability
and listening to bill is very sound advice
the cut-out sounds like a very good idea, i have heard of people with electric cut outs, how does that work, and how expensive is that usually in a ballpark figure
if it can't win a race it better win a show
I dynod a gain in hp all over the band going from a 2.5 downpipe back to 3" downpipe back, how ever torque did suffer a little,but I felt the gain in mid and high end hp was worth it. I wont ever go anything smaller then 3 inch on a turbo car regardless of power. Unless its like 150 whp lol
LE61T PTE6262 Powered 
Vincent Morris wrote:your exhaust is only as big as your smallest size.
for example, if you have 3" pipe and a 2.5" downpipe. its only going to give you the gains for a 2.5" system.
im running 2.5" turbo back and im fine with it, people say i need 3, but i dont need anything. i like it how it is.
I don't agree with this... IMHO... you're moving more air with 3/4 of your system 3" then if your entire system was 2.5"
but as vince said it's users desire not mine or his or bills, what you want is what you get
LE61T PTE6262 Powered
In practice, a 2.5" downpipe to 3" catback system will flow more than if it were 2.5" all the way, and less than if it were 3" all the way. The total restriction of an exhaust system is the sum of all its seperate pressure drops, so mixing this way can still work well. Don't start with a bigger pipe and then go to smaller (such as 3" downpipe to 2.5" exhaust). That's just ineffective, unless it is temporary until one ultimately gets the 3" catback.
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com
