Question, i went from single cam to b20 swap recently, and my header is 2.5 outlet 4-1 which goes straight into my stock cat with 2" piping to a gsr muffler......The question is, is that too small to be running my b20? it kinda feels like its restricted and i just dont know what size of piping i should get or if this is really the problem.....Please give me your feed back.....

92 civic eg b20z Stock DD

 

That is not too small to run....it may feel restricted cause in actuality...it is. Stock piping is 1.75"...do you know the basis on why it was upgraded to a 1/4" bigger? Waste of $ IMO. Unless you have plans to build the motor, and add some compression, get 3". If you dont and just want to keep adding bolt on's as a fun daily driver, just get 2.5".

 

The exhaust came on the car when i got it....Worked good for the SOHC....Anyone else think i should stick with the 2" or go bigger? I really dont want to go with a bigger exhaust....maybe replace the stock cat with a test pipe? I dont know guys, help me out.

 

I had the same question and ended up going with 2.5" all the way through. I'm still on my stock P75 ecu, and honestly, I couldn't tell a difference. As a matter of fact, it felt like I lost power from 1~4k rpm, but that's my unscientific, butt dyno talking.

I say just rock what you got until you see someone selling a cheap 2.5" setup locally. Or buy a cheap 2.5" ebay setup and change the muffler.

 

I would get a new exhaust. If your header has a 2.5 in. collector and it is connected to a 2 in. cat, there may be a bit of a leak in there somewhere. I am betting that you would notice a difference between the two. I have never messed with a 3" exhaust as I have always been told by my tuner that 2.5 is plenty large enough for most all motor applications.

How about trying an exhaust shop? Cheap, quick, and essentially accomplishes the same goal. Cheaper than buying a stainless brand name exhaust. The reason that it seems like you lose pressure when increasing the diameter of exhaust is because you usually lose low-end torque and power. Honda's aren't really known for great low end power anyways, but the larger diameter will give you the power up top where you need it (especially with a b20).