2.25" exhaust to 2.5" exhaust.. Worth it?
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From: North Carolina
2.25" exhaust to 2.5" exhaust.. Worth it?
Wondering if it would be worth my while to switch to a 2.5" exhaust? At the moment I have the GM Performance exhaust which is 2.25". Any comments or suggestions are welcome! Mods are in sig.
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From: Cincinnati, Ohio
im full bolt on, 2.6 pulley with header and dp with the gmpp and i have no problems... love the sound, best if herd... i cant see 2.5inch making that much of a difference. i would say its not worth the extra money for a new 2.5 catback
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From: Los Angeles, CA
full 2.5 exhaust is ideal for my setup... "2.9, 42.5s" but everyone is entitled there own opinions...
bigger the exhaust piping diameter, the more back pressure lost. the more back pressure lost, the less PSI output.
So in turn you will put out less PSI. So for instance, I'm running a 2.9 pulley. I'm roughly 1200 ft elevation above sea level. I put out 16 PSI with a full 2.5 exhaust.
Basically, opening up the diameter of your exhaust piping allows for a safer more efficient way to make power when dropping in pulley sizes, etc.
maybe some of the big wigs on this site can pitch in...
bigger the exhaust piping diameter, the more back pressure lost. the more back pressure lost, the less PSI output.
So in turn you will put out less PSI. So for instance, I'm running a 2.9 pulley. I'm roughly 1200 ft elevation above sea level. I put out 16 PSI with a full 2.5 exhaust.
Basically, opening up the diameter of your exhaust piping allows for a safer more efficient way to make power when dropping in pulley sizes, etc.
maybe some of the big wigs on this site can pitch in...
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I normally stay out of the LSJ section since I don't have much experience with it but I have CED's 2.75" cat-back exhaust and I'm happy with the performance I feel. I'm still running the exhaust through the GMPP ext-honed manifold and Original DP so there's still a restriction for the "acclaimed" backpressure. Having a larger pipe allows for more gas removal but the sound is harder to keep quiet. I do not feel a loss in low-end power so I can't see what harm a 2.5" exhaust system would do for a 2.0SC.
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From: tucson
be carefull with custom exhaust..i just payed 100 bucks in labor for a guy to cut before the axle were the exh. narrows to 2.25..and when they compressed bent the pipe the crunched way more than the stock one did to get over that rear sway bar...so now i have an exhaust that gets supper narrow then goes back to 2.5..i wish i went with a megan or something mandrel bent....or tell them to use 3 inch for the part that goes up and over the rear axle..that way when it is compressed and shrinks it would be aroun 2.5..better than big than small..
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From: Az
Does anyone really know what the GMPP exhausts flow? We really need a before and after dyno from someone that went from a GMPP to a 2.5 to see. I doubt it's really a huge HP increase. 5-8 hp maybe?
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From: Norcal east bay area
With stage 2 and a 2.9 pulley it doest make enough hp to be choked using the 2.25|" GMPP exhaust cause the stock exhaust manifold is the bottleneck. If you run a header maybe then the "choking" would be the 2.25 pipe and bends down the line..
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From: Cincinnati, Ohio
what ever... you dont even know what ive got done, so i wounldnt say anything... im just trying to help a guy out... and its not worth buying another catback for a few hp
plus i get good back presure but not to much... its not like we are turboed
plus i get good back presure but not to much... its not like we are turboed
Last edited by quadracer0387; Feb 25, 2008 at 11:51 AM. Reason: Automerged Doublepost
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From: Edmonton
and if you were looking to prove to the ss/sc community you know nothing about modifying then you have succeeded. your running a 2.5 inch or 3 inch dp with manifold, yet you think that the 2.25 is fine? WOW
TO ANSWER THE QUESTION.. if you plan on anything over a 3" pulley and no tune, like stage 2 and up, yes the 2.5 would be beneficial. The 2.25" gmpp was originally designed for the ss/na not the ss/sc, it just so happened to fit, and people that it was smart to buy it.
smaller pipe=less flow, less air going out = less air able to come in less air coming in= less power.
the concept is simple.
290 with no meth? you are on glue
me and black 06 and jmac all ran 2.6 setups with full exhaust and meth and all came in in the 290+ whp zone, with ur heat soak and lack of timing youd be lucky to see 265 whp.
sorry to burst your bubble.
you realize that a larger exhaust will drop temperature #'s add to maximum flow, create a larger avaliability for intake air flow.
If the 2.25" gm is so amazing, why is the stock exhaust system mostly 2.5 and 2.75inch piping? SEEMS REALLY dumb to add parts and close off flow.
I should take my 3 inch off my srt-4 stage 3 and put some 2.25 inch on there, i bet my power numbers would be insane!
for those counting, you posted 3 times, and were wrong 3 times
sorry bro. you struck outdont be hating cause you have the 2.25 inch gmpp, we both know u know u should have went bigger, its okay ****
p.s. i can get u a nice one at a nice price when u decide to upgrade
Last edited by MatrixMotorsports; Feb 25, 2008 at 02:02 PM. Reason: Automerged Doublepost
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From: Canada
turbo exhaust is very different to s/c or N/A
you should know that matt.
bigger isnt always better.
for a 230-250hp cobalt, the price/sound/performance of the gmpp catback is pretty darn good.
and a 3 inch, would be a bad choice.
and no im not just saying this.
I spent the money and proved it to myself.
Im not worried about my gmpp one little bit, as thats not where my exhaust comes out when im racing.
you should know that matt.
bigger isnt always better.
for a 230-250hp cobalt, the price/sound/performance of the gmpp catback is pretty darn good.
and a 3 inch, would be a bad choice.
and no im not just saying this.
I spent the money and proved it to myself.
Im not worried about my gmpp one little bit, as thats not where my exhaust comes out when im racing.
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Joined: 02-07-08
Posts: 271
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From: Edmonton
full 2.5 exhaust is ideal for my setup... "2.9, 42.5s" but everyone is entitled there own opinions...
bigger the exhaust piping diameter, the more back pressure lost. the more back pressure lost, the less PSI output.
So in turn you will put out less PSI. So for instance, I'm running a 2.9 pulley. I'm roughly 1200 ft elevation above sea level. I put out 16 PSI with a full 2.5 exhaust.
Basically, opening up the diameter of your exhaust piping allows for a safer more efficient way to make power when dropping in pulley sizes, etc.
maybe some of the big wigs on this site can pitch in...
bigger the exhaust piping diameter, the more back pressure lost. the more back pressure lost, the less PSI output.
So in turn you will put out less PSI. So for instance, I'm running a 2.9 pulley. I'm roughly 1200 ft elevation above sea level. I put out 16 PSI with a full 2.5 exhaust.
Basically, opening up the diameter of your exhaust piping allows for a safer more efficient way to make power when dropping in pulley sizes, etc.
maybe some of the big wigs on this site can pitch in...
and i big wigged up for ya.
turbo exhaust is very different to s/c or N/A
you should know that matt.
bigger isnt always better.
for a 230-250hp cobalt, the price/sound/performance of the gmpp catback is pretty darn good.
and a 3 inch, would be a bad choice.
and no im not just saying this.
I spent the money and proved it to myself.
Im not worried about my gmpp one little bit, as thats not where my exhaust comes out when im racing.
you should know that matt.
bigger isnt always better.
for a 230-250hp cobalt, the price/sound/performance of the gmpp catback is pretty darn good.
and a 3 inch, would be a bad choice.
and no im not just saying this.
I spent the money and proved it to myself.
Im not worried about my gmpp one little bit, as thats not where my exhaust comes out when im racing.
anything over stock would benefit for the 2.5, or stay at stock, dropping doesnt make sense. Jonny mad power on it at STOCK tables, not modified, so his numbers are USELESS.
The cost factor i agree is nice, and remember im not speaking from my turbo expertise, i drove a heavily modified lsj for a long time
Last edited by MatrixMotorsports; Feb 25, 2008 at 02:07 PM. Reason: Automerged Doublepost
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From: Canada