Exhaust Sizing Question..

LSiNtegraDB7

I enjoy Integras.
Quick question guys; right now I have a 2.5" 4-2-1 header, and I recently picked up an Apexi N1 cat back to replace my ebay/greddy setup. The seller included a resonated test pipe that matches the Apexi's 60mm also. My question is if you guys think it would be better to run the stock cat or the test pipe? I know the inner diameter of the header is very close to the apexi's size, but would throwing the stock cat in between cause a bad bottleneck? If I use the resonated test pipe I'd almost have exactly the same size from the header back. Plus I figure since it's resonated it probably won't alter the sound that much.

Any opinions?
 

jznsn2u

Active Member
If you use the stock cat, you would be bottle necking and that's bad. If you put in your test pipe with a 2.5 exhaust size, don't be surprised if your car is very loud. Does your state require smog?
 

Samurai_Blue

Yolo Whippin'
just get a universal cat and get a bigger flange on the header side. Your car will lose power going the power band with a test pipe since its stock.
 


LSiNtegraDB7

I enjoy Integras.
jznsn2u said:
If you use the stock cat, you would be bottle necking and that's bad. If you put in your test pipe with a 2.5 exhaust size, don't be surprised if your car is very loud. Does your state require smog?
Click to expand...
Well It's not really 2.5". The header's outer diameter is 2.5" so the inner diameter is a little less than that. The Apexi piping is 60mm, so right about 2.36". I'd be able to get away with it if I use an O2 sim or something I think.

Samurai_Blue said:
just get a universal cat and get a bigger flange on the header side. Your car will lose power going the power band with a test pipe since its stock.
Click to expand...
I thought about getting a high flow cat but for now I'll just use what I have haha. Also, how would I lose power? Wouldn't the exhaust size be right about perfect for an LS with bolt ons?
 

Samurai_Blue

Yolo Whippin'
the test pipe somehow makes you lose mid range. I forgot how but i tested it and i have more torque with my cat in.
 

ixcocoyxi

RS owner
see if you could sell the test pipe and pick up a matching size high flow.
 


jznsn2u

Active Member
You're saying your header is a bigger diameter than your mid pipe right? That's called bottle necking. To be honest, on a stock ls the most I would go is 2.25.
 

ixcocoyxi

RS owner
as a matter of fact, i say fuck it and run a test pipe. pop flames!!

every now and then, my exhaust will pop super loud when i shift driving normal. i get super excited when it does.
 

LSiNtegraDB7

I enjoy Integras.
ixcocoyxi said:
see if you could sell the test pipe and pick up a matching size high flow.
Click to expand...
Yeah I might do that. I just hate to spend more money now that I got the exhaust; I already have to get an extension for it to fit the DB.

Edit:
ixcocoyxi said:
as a matter of fact, i say fuck it and run a test pipe. pop flames!!
every now and then, my exhaust will pop super loud when i shift driving normal. i get super excited when it does.
Click to expand...
Your running a test pipe?

jznsn2u said:
You're saying your header is a bigger diameter than your mid pipe right? That's called bottle necking. To be honest, on a stock ls the most I would go is 2.25.
Click to expand...
Somewhat, but by a few mm. If the outer diameter of the header is 2.5", wouldn't the inner be around 2.38"? Which makes it .2" larger than the Apexi's 60mm. I would think that would be fine.
 
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