OK, I need some in good solid opinions.... I'm somewhat of a perfectionist and I've been wrecking my brain trying to make sense of this. I've been searching for threads on the whole exhaust piping and backpressure thing. And i dont' know what to do. I've ordered a ZZP Header 3" collector with Downpipe 3" weld in end and I was gonna go 3" straight pipe....so pretty much 3 Inch all the way through.... because I figured I would get more HP gains then going with 2.5" all the way through. The way I look at it you see these 400 horse muscle cars with dual 3" straight pipes and they have no problems. So why can't I have one 3" pipe with all my engine mods I will be reaching somewhere in the area of 280HP and i will be burning alot more exhaust then factory would of and my boost will be alot higher like around 18PSI.... So what do you guys think of going 3" straight pipe with the heavy Mods I have????? Will I be losing power somehow?? Do I need more back pressure?? Any suggestions would greatly be appretiated.... People please only the facts or if you know what you are talking about... thanks

 

What do you have for mods?

In all honestly I don't think you need a full 3" until over 300whp. Not that you won't see gains, but you will see them in the upper RPM range.

 

I second that..2.5" should be plenty good, unless you have some damn good mods.

 

Also the Stock setup is not fully 2.5", it varies in size. You will gain power from a full 2.5" exhaust.

 

I will second and third those statements... A full 2.5" exhaust should be plenty unless you are running over 300HP! There is nothing wrong with 3" but you won't notice any gains untill the top end, you will prolly loose some low end power with 3" over 2.5"

 

Compromise and get a 2.75" exhaust. Dezod sells one BTW.

 

I'm expecting my new 3" Downpipe and 3" Exhaust this week. Look for another of my reviews on the frontpage sometime next week.

Factory is a kinked Downpipe with 2.5" piping with a over the rear axle 2 1/4" piping with a very bad muffler design. A true 2.5" will help but in my opinion a waste of money if you plan on making more power than factory.

Going from 11-12PSI factory to over 17PSI that's a lot more air being pushed threw the engine, I say buy the 3" now and save money down the road.

 

Stick with the 2.5 exhaust all the way through. I have more hot rod toys than just a supercharged cobalt. From experience you need at least 450 real horses to get any justice from a 3 inch exhaust. I can guesstamate that even if you could find a way to make close to 300 horses out of your cobalt you would still not see a gain with 3 inch.
Good Luck!

 

if you're planning to be in the 280 hp range, don't get a 3' exhaust... 2.5 is enough untill you're talking about a lot of mods, and probably over 300whp range... if your'e realistically going to be over 300, then get the 3', otherwise, don't bother because it will hurt more than it will help

 

Guy's please read this REAL experience review with REAL dyno results before you start telling people a 3" will do nothing.....
https://www.cobaltss.net/forums/show...&highlight=cti

hurt more then help?!? wow.

 

ok, so you're saying that ONE car making about 8 hp with a header and catback is a good gain? 8 hp for those mods is not a good gain at all... guaranteed with a 2.5 he would have made more power...

most people gain 8 hp with JUST a catback... jony b gained 12... so yes, i stick with my original statement...

 

I will state from my experience that 3" sacrifices low end torque Noticeably, I don't have dynos but I can feel it i have full three inch and you floor it at about 2000 rpms in second gear and it doesn't build like the stock exhaust the upper rpms seem stronger but not worth it IMO,

I'll most likely be going with the vibrant h/dp and custom 2.5" with borla muffler, in the near future.

but this is just my 2 cents.

 

When I had my 3" altered atmosphere exhaust, My car felt really really slow, I actually felt a little increase when I switched to magnaflow 2.5"

 

my small bit of input will be that gmpp catback exhaust yielded around 15-18hp (crank)peak on my aeroforce interceptor guage (yes i know its not super accurate...)

 

yep... GUARANTEED he will better gains from 2.5. I would like to see zinners response to these posts

 

My Mods this far: K&N air Intake, 2.6 pulley , #60 injectors, 2 step colder plugs, adj tensioner, ZZP Header with 3" downpipe....

So with the replys of the majority I get the feeling 2.5" straight pipe exhaust would be the most suitable?

 

I think so. Maybe a 2.75, but 2.5 should be great IMO.

 

The Cobalt Grand-Am Cup cars went from 3" pipe to 2.5" for a reason! The gains were better all the way around. Why sacrifice when you can have your cake and eat it too! 2.5" FTW!