I have a mildly modified b16 (1999 Si), with CTR/ITR valvetrain and cams, dynoing 167 WHP. I am currently running a JDM 4-1 header and 5zigen fireball exhaust. I was considering changing my exhaust. is 2.5 inch piping too big for my application?

 

167whp - in my opinion - is enough for 5zigen to handle

 

2.5inch would be just fine.

 

 

Since you already have an exhaust you can save some money and buy another mod. Unless you plan to make a lot more whp in the future.

 

i dont think 2.5 in piping for a mild setup like that is necessary.....i would just stick with 2.25 in. piping

 

Your exhaust is fine.

 

You make 167 whp with CTR cams? Can you list your mods. I agree with Exody, your 5ZIGEN exhaust should be fine for your application..

 

My setup is as follows:

CTR Cams
ITR Intake Manifold
ITR Valves and valvesprings
11:1 Compression
3 angle valve job
JDM 4-1 with modified stock cat
5zigen Fireball
Comptech Icebox intake


I am probably closer to 170 now without power steering. I also have a spoon TB on the way. I was thinking about getting a new cat to match my header, but I am hesitant to do even that if it is all going into 2.25 inch piping anyways.

Thanks for the input. This is why I hang out in this forum instead of the EG forum.

Cruzer

 

Nice #s. How did you get the 11:1 compression? Milled head, thinner headgasket? You are still using stock (b16) pistons? Thanks..

 

2.5 would be fine

 

I raised compression by milling the head.

It seems like 50 % feel i need to go to 2.5 , and the other feel 2.25 is fine....hahahaha

 

60 mm

 

Would a 2.5" loose some low-end compared to a 2.25" with his particular application?

 

60mm piping is more than enough for your mods. I believe the 5ZIGEN fireball piping is 60mm. Most of the aftermarket exhausts like GReddy, Tanabe, APEXi, Skunk2/RSR, etc. are 60mm, aprx. 2.38" diameter piping. I think Thermal R&D uses 2.25" piping. You can't go wrong with either, but 60mm is more than enough..
How much was the head milled?

 

I believe the head was milled .30, just enough to bump up to 11:1 where it would be safe to run 91 or 92 octane gas, and just enough so that i could run bigger cams if i wanted to.

Thanks for all the info...

Cruzer

 

modifed stock cat? man ditch that thing for a carsound 94006. 170whp+ is yours.

 

2.5 would be nice.

 

Get a new cat