I just realized I have 2.5 intake, 2.5 throttle body, ported plenum, ported lower, stillen headers, and 2.5 hfc. But went cheap on exhaust (topspeed pro 1 cat back) and its 2.36 not quite 2.5.

Is it worth the upgrade to 2.5? Or is the difference of 0.14 of inch not something to worry about? I'm pleased with the sound of pro 1 but on the hunt for some extra power. Figured I'd ask around the forum, I would think the 2.5 would make more power just not sure if it would make 1hp or 10hp more.

I couldn't find what Topspeed claims to make for a 2.36 but as reference stillen claims 18 with their 2.5

Help!

 

Short answer: no , it's not worth the extra money.

 

5" straight pipes or go home.

 

Lol. Ended up getting the stillen. Hope it fits the X sedan!

 

Exhaust does not have to be as large at the intake due to working pressures. You have over 200 psi pushing spent exhaust when the exhaust valve opens. Pressure drops quite a bit by the time you reach the muffler, but still... Absolute best intake working pressure you can get on a naturally-aspirated engine is 14.7 psi.

 

I assume you mean 14.7 psia (absolute, or about 0 psi gauge)
A stock G37 at wide open throttle has about 1.8 inches/Hg (0.9 psig) intake vacuum. (well, that is what I happen to recorded today for a different reason )

 

I meant dP, i.e. the amount of pressure head to push air into the cylinder. The difference of a perfect vacuum in a cylinder to atmospheric pressure. Realizing, of course, that perfect is unattainable and real engines have reversion to further lower dP.