2.5 inch pipe with exhaust... Do or Don't?

[ERIKbronx]

My local muffler shop is going to put on a 2.5inch pipe from behind my cat going to my OBX exhaust for $140, or just add the exhaust for $65. What will I be the gain of the 2.5inch pipe?

[jmgladden]

From what I have read, 2.25" is best for a N/A car.

As old as the piping is on your car, almost ten years, I personally would go ahead and get some new piping along with the muffler.

[TurbochargedSER]

J Gladden is correct, have them run 2.25" piping since the car is N/A!

[P10 WRC]

what is n/a?

[NismoPC]

Originally posted by jmgladden
From what I have read, 2.25" is best for a N/A car.

As old as the piping is on your car, almost ten years, I personally would go ahead and get some new piping along with the muffler.

Strange this should come up. In the May 2002 Issue of Sport Compact Car under Letters, Page 26, Bill Luton, Pres. of Bill's Isuzuperformance.com did some dyno tests and Bill came up with a whole different picture on exhaust diameter.

You should really get this and read it.

He was able to prove that (or should I say recommend) the following should be the standard:

- 2.5" diameter for all 1.5 to 2.5 liter NA engines as the minimum size
- Any thing larger than 2.5" for 2.6 litre NA engines and larger

So with that said, I am still gonna keep my 2.25" piping and wonder if Bill was right about the 2.5". =)

[NismoPC]

Originally posted by P10 WRC
what is n/a?

Normally Aspirated.

Meaning, no forced induction of any kind (turbo or supercharger)

[JustinP10]

Originally posted by NismoPC


Strange this should come up. In the May 2002 Issue of Sport Compact Car under Letters, Page 26, Bill Luton, Pres. of Bill's Isuzuperformance.com did some dyno tests and Bill came up with a whole different picture on exhaust diameter.

You should really get this and read it.

He was able to prove that (or should I say recommend) the following should be the standard:

- 2.5" diameter for all 1.5 to 2.5 liter NA engines as the minimum size
- Any thing larger than 2.5" for 2.6 litre NA engines and larger

So with that said, I am still gonna keep my 2.25" piping and wonder if Bill was right about the 2.5". =)

Nope, he's wrong =) Go with 2.25" There's been a lot of testing about this, and 2.5 is too large for the SR20 motor when it's N/A. Even with full bolt ons they said that 2.5 lost more low end than it gained up top over the 2.25.

[NismoPC]

Originally posted by JustinP10


Nope, he's wrong =) Go with 2.25" There's been a lot of testing about this, and 2.5 is too large for the SR20 motor when it's N/A. Even with full bolt ons they said that 2.5 lost more low end than it gained up top over the 2.25.

That is exactly why I am keeping my 2.25" set up. Fully satisfied with it.

Still was a good tidbit of info for others though.

[G-loads]

Mike Kojima suggested that for pipe diameter:

1500cc - 2000cc motors, use 2 inch
2100cc - 2500cc motors, use 2.25 inch
2600cc - 3000cc motors, use 2.5 inch.

So these info is inlined with what the 2.25" on n/a car you guys are running. Just remember: if the exhaust pipe is too large, the flow will be sluggish with low velocity and the scavenging will not be so good, unless you're turbocharging!! A good exhaust has low backpressure and high velocity!!!

[NismoPC]

Originally posted by G-loads
Mike Kojima suggested that for pipe diameter:

1500cc - 2000cc motors, use 2 inch
2100cc - 2500cc motors, use 2.25 inch
2600cc - 3000cc motors, use 2.5 inch.

So these info is inlined with what the 2.25" on n/a car you guys are running. Just remember: if the exhaust pipe is too large, the flow will be sluggish with low velocity and the scavenging will not be so good, unless you're turbocharging!! A good exhaust has low backpressure and high velocity!!!

Yea, Bill even referred to Mike Kojima's suggestions in his letter and stated that he feels Mike's calcs are off by .25-.50". Ouch!

Pretty bold statement. Don't you think? Personally, I am sticking with Kojima's research. He has been proven.

[flyg20]

Originally posted by P10 WRC
what is n/a?

?????

[NismoPC]

Originally posted by flyg20


?????

I answered that above. :cheeky: Look up ^

[G-Forces]

Originally posted by NismoPC


Yea, Bill even referred to Mike Kojima's suggestions in his letter and stated that he feels Mike's calcs are off by .25-.50". Ouch!

I'd stick with the 2.25" too. We all seem to be in agreement. Although Bill Luton got great peak number he didn't stat what his low/mid range loses were. Bigger piping is always good for peak power. NismoPC already stated the low/mid velocity argument. ;)

[flyg20]

Originally posted by NismoPC


I answered that above. :cheeky: Look up ^

i know that, i just posted some playful mockery for a dumb question

[NismoPC]

Originally posted by flyg20
i know that, i just posted some playful mockery for a dumb question

Smart ass! :cheeky:

Actually, there are some newbies on here that do not know a lot on car talk, gear heads, and monkey wrenching. So be nice!

Hold on! Let me read that again!

Originally posted by flyg20
i know that, i just posted some playful mockery for a dumb question

Hehehe! Now I find it funny!

[casey mathias]

ive always heard 2.5 with cams.... 2.25 w/o

[Glowmunkey]

Originally posted by ERIKbronx
My local muffler shop is going to put on a 2.5inch pipe from behind my cat going to my OBX exhaust for $140, or just add the exhaust for $65. What will I be the gain of the 2.5inch pipe?


Just make sure it's mandrel bent 2.25". If it's crush bent, I wouldn't even bother.

[NismoPC]

Interesting. This thread is almost like an anniversary thread. It was posted March of 2002 and got a reply in March of 2003.

Well, now make that three replies.

Happy Anniversary thread!

Wonder what ERIKbronx ended up doing last year. Hehehe!

[Glowmunkey]

Damn, didn't even notice... see kiddies? Don't drink and surf.

[ERIKbronx]

Originally posted by NismoPC
Interesting. This thread is almost like an anniversary thread. It was posted March of 2002 and got a reply in March of 2003.

Well, now make that three replies.

Happy Anniversary thread!

Wonder what ERIKbronx ended up doing last year. Hehehe!


LOL, I was like whoa!:confused:

I did the 2.25inch crush pipe with my obx exhaust last year:p

This year im gonna do a Hot Shot Header and CAI, with stock piping and a Remus exhaust. Thanks guys for bring back memories, I was wondering how long its been since I installed my current exhaust.:p

P.S. my current setup is kool, a little loud but kool, I love it, I don't know about the people driving besides me tho, oh well pedal to the metal.... Bye:evil::p

Next year they just might hear... tssshhhhh!:p

[JustinP10]

Yeah, there were quite a few OLD threads that resurfaced recently.

[Trag]

http://www.se-r.net/car_info/engine_performance_tuning.html#Exha ust%20Systems

Well i hoped the linked worked, anyways it says that 2.5 is the way to go because if you have a stock motor and going to keep it stock then stick to 2.25, if you have some work like the extras which most of us have anways then get the 2.5, youll increase just as much as putting headers on.

Good luck

BTW im getting my exhaust done in mandrel bend 2.5 inch (no kinks or crushes) done really soon, cant wait.