can anyone say for sure that 2.5 inch is better than 2.25 and a quarter for our car. I know that 2.5=more exhaust flow but I also now that lots of times people say that bigger is not neccesarrily better for 4 cylinders because they need backpressure. I'm wondering because I did a 2.5 inch axleback with a magnaflow muffler but I keep thinking that maybe my car would respond better with 2 and a quarter. I've been thinking a lot about getting the gm exhaust. I love my car but I've always felt like it lacked torque, it feels like a bitch off the line. Once it's going it's great, but I keep thinking the smaller exhaust pipe will help. Does anyone have any dyno numbers to compare. I know that on the dyno it seemed like my car's torque dropped off a lot after 5000 rpms. Anyone have any input(hoping for input based on numbers not their opinion on how they like their exhaust, no offense)

 

nah you wont have any problems with backpressure on a 2.4 with a 2.5" piping...however if it were 3" then youd have backpressure problems

 

What If I add a 4-2-1 header and downpipe with a high flow cat? I already have the Corsa CB.

 

I have a 2.5" all the way back and my car runs great! I wouldn't go any bigger though.

On a stock 2.4 with no other mods planned the 2.25" would probably be a better choice - not because of backpressure, but because it maintains exhaust velocity better (due to less cooling) with less exhaust volume.

 

well i have the weapon r intake, gm header, and downpipe with high flow cat from zzperformance. I'm not planning on anything else except for maybe a tune. So what do you think 2.25 or 2.5

 

no from everything ive ever heard the exhaust mani. shouldnt make a difference and the catless downpipe isnt any different really...its just missing a cat...whichi is a converter...it doesnt build up pressure or anything...the only real worry is to bigg catback piping

***2.5" piping most definately....theres no gain ina 2.25"***

 

I can't believe no one has said anything on this...

The reason to upgrade your exhaust is to get rid of backpressure. Backpressure is a negative effect. Restriction causes backpressure. The bigger the exhaust system, the less backpressure being created BUT you want to maintain a certain exhaust velocity...this is why you shouldn't get the largest exhaust system possible. It's a balance between the two you want to maintain.

 

you should only go with 3.0 exhaust if your making more than 250 whp, if your under the i think you should run 2.5

 

I'm but even if he was making remotely close to that much power, his exhaust system isn't restricting him from making more power. There are more factors that play into what exhaust you should have for different setups.

 

i completely agree, if you go bigger diameter you lose a little response o the low rpms but make it up on the top end, 2.25 excellent response off the throttle but not as much gains on the top end, 2.5 all around performance off the line and top end as well. at least thats my opinion

 

Yes but it depends on the vehicle of course. In his situation, yes.

I just wanted to further clarify that situations change with different vehicles and setups.

But yes, you are overall correct.

 

 

This makes sense, so if no one understands, its cool. The piping on the G6 GT (224hp V6) is 2 1/4. Having said that, the piping on a Grand Prix GTP (240hp S/C V6) is 2.5". Unless you plan on taking modding your car heavilly in the near future, a 2 1/4" system that is fully mandrel bent with a high flow (or no) muffler, you will not be dissappointed. 2 1/2" wont hurt performance, but the 2.4L seems to lack torque, and a sliiiighty smaller exhaust may benefit until you release that upper RPM bottleneck these engines seem to have. (basically cams, tune, and maybe some headwork)

Just some food for thought.

 

NJHK, how much do you think a GMPP catback would hold me mback on my setup + a 2.9 pulley. Would I benefit alot from a 1/4 mile standpoint? I dont care for dyno's Short answer... I really dont want to steal the trend...

 

What is the size the GMPP exhaust?

 

2.25... Like I have 2.25, how much if any would i benifit from 2.5. I think 3.0 would be to big for my car

 

To me it sounds like it wouldn't differ from your stock exhaust system.

You might want to go for something larger, a full 2.5" should be fine.

 

Damn, well I have bought the 2.25 now allready, other (excluding GMPP) cat's are really expensive in Canada. OH well, guess it'll have to do Thanx for the help anyways!!

Sorry guys, didnt want to jack the trend (2.4)... you can delete these replies if you want!

 

if i were you i would keep the cat and run 2.5 all the way back to a strait through muffler. you might lose some torque but you will love your top end.

 

It's alright.

 

basically 2.5 is the way to go......no sense in putting a full 2.25 on bec ause it wont really make a difference.....especially as far as a ss/sc goes...you definately want to put on a 2.5"....and if your going to push out more than 250-275 horesepower go with a 3.0"....but to the original poster go with a 2.5"....i put it on mine....went with the corsa....and there is a very noticable difference in torque all thw way through the band....and it even feels to me like it smoothed out that rough 1st gear shift.....

 

i agree

 

I get the logic behind going 2.5 inch. I am just exploring the idea of 2.25 because I see a lot of people hear talk about how much they love their gm exhaust. I know that on my neon when I went from just a performance muffler to a 2 1/2 inch cat back my car felt slower(granted I know this car has a great deal more power and displacement then a neon). I am just curious to see if any one with a 2 1/4 exhaust has any numbers before and after(dyno or quarter mile, whatever). I understand the science behind it and the benefit top end, but I would like to hear from some people with 2 1/4 just to see how their cars responded to it.
Too be honest if its not much of a difference I might want to go 2 1/4 just to make it feel more responsive cause it definitely lags off the line(and just in case any one is wondering I do know that I need to lauch from L not drive, I do know about the t/c, still feels slow of the line).