2.5 or 2.25

[XAlliedYouthX]

Which is the better size piping for the 2.4? I've read that 2.5 is "dyno proven" to give the best results on a semi-stock engine. I've also been told that 2.5 is to big and 2.25 is better. Are there any hard results that I can see to help me make a decision on my exhaust size when I get it done?

[The Artist]

spyhunter goes w/ the 2.5 theory. I dont have an answer, but most people that i have talked to say that u dont need anything bigger than 2.25 cause u need the back pressure. I'd say the best place to get ure answer is over at quad4forums.com though...since its only 4 banger related

[jayhawk]

Thats a toughie; it really depends on what you do to the engine, because in some cases bigger is not always better.

[Blackrider]

Originally posted by sweet98gagt
spyhunter goes w/ the 2.5 theory. I dont have an answer, but most people that i have talked to say that u dont need anything bigger than 2.25 cause u need the back pressure. I'd say the best place to get ure answer is over at quad4forums.com though...since its only 4 banger related
You dont want ANY backpressure!

[VanishingImage]

I went with 2.25 on my exhaust setup. I only went with the 2.25 because for one, I don't have a built up engine,only have a AEM air intake, and second, with a 4cyl its not really going to help,now if it was built up with some major horses then yea 2.5 would prolly help,but in a stock engine 2.25 is prolly the ideal size. I noticed some improvements when I went to the track last year,plan on hitting it a lot this spring/summer to find out how much it really helps.

[azeniskid]

Originally posted by Blackrider
You dont want ANY backpressure!

what he said....



2.3 intake mani,
t/b,
good intake,
secret cams,
header,
yeah you'll want a "bigger exhaust".

[urweak]

im going with 2.5 myself, for one the shop i find to do the work will probably do crush bends which will redtrict flow alittle, so the bigger pipe will offset that alittle. And i plan on having more then just an intake or whatever done to the car.

And i read something somewhere maybe SCC a car with more liters is going to want bigger pipe.

[92CamaroRS]

if you want power at the HIGH rpm go with the 2.5
if you want power at the LOWER rpm go with teh 2.25


backpressure is REQUIRED if you want to retain any amount of torque.

the only time you cant go too big is with a Turbo.

[XAlliedYouthX]

The results have lead me towards 2.25. Now I just have to buy my mandrel bends and get ready for summer time.

[1996v6corsica]

go with the 2.25.. i know how an I4 runs with no backpressure :]

back when i first got my celica, there was a piece of flexpipe just behind the cat, that rusted and blew off in a parking lot... the car lost all of its low end oomph.. like.. all of it.. i dont know if it helped the top end at all.. i couldnt get there... anywhere past 3,000 RPM was deafening inside the car, i got it fixed in the morning :]

[Blackrider]

Originally posted by 92CamaroRS
if you want power at the HIGH rpm go with the 2.5
if you want power at the LOWER rpm go with teh 2.25


backpressure is REQUIRED if you want to retain any amount of torque.

the only time you cant go too big is with a Turbo.

Backpressure is almost becoming a Ricer term. Backpressure is bad in any form. It’s called Exhaust gas Velocity!

[92CamaroRS]

Originally posted by Blackrider
Backpressure is almost becoming a Ricer term. Backpressure is bad in any form. It’s called Exhaust gas Velocity!


and withough changing the heads or pistons, backpressure, TO A CERTAIN EXTENT, is detramental.

[azeniskid]

um.... backpressure bad..... high exhaust velocity good.....

[99blackSE]

im getting 2.25 inch on my 3400 but i just have an RSM intake so...
and 99% of my driving is not even close to 3k rpm or above so...

[Matt95GT]

On an automatic 2.3 or 2.4 I would not go larger than 2.25".

[XAlliedYouthX]

I want to go with 2.25 mandrel but the bends are so damn expensive but if I were to go with 2.5 crush bent wouldn't the creases in the bends make it almost as if it was 2.25??

[DontPassTheFence]

i was thinking about that crush bend theory as well, since I am in fact too poor to have an exhaust shop bend up 2.25 mandrel bends.

[MagusXIII]

Originally posted by XAlliedYouthX
I want to go with 2.25 mandrel but the bends are so damn expensive but if I were to go with 2.5 crush bent wouldn't the creases in the bends make it almost as if it was 2.25??
To an extent, that is true. But with crush bent pipes, the restriction will introduce turbulence. This can slow down the exhaust velocity somewhat compared to 2¼" mandrel bent tubing.

[XAlliedYouthX]

Originally posted by MagusXIII
To an extent, that is true. But with crush bent pipes, the restriction will introduce turbulence. This can slow down the exhaust velocity somewhat compared to 2¼" mandrel bent tubing.

That was something I was thinking could happen

[DaemonGA]

My GA is running on 2.5 cuz of my v6 so i already tried 2.25... it backpressure too much... got oil leaks into my exhaust manifolds once so i switched to 2.5 so it worked so great :) so if your car has an turbo or supercharger... go with 2.75 for sounds of high pressure of turbo/ SC of whining and loud pitch tone...

P.S. Oil leaks is cause of piston rings worn out cuz of that 2.25 so i had to tear my engine apart to replace rings with JE piston rings... they runs good from now on.... 108k on my car but 15k on my rebuilt engine