2.5" vs. 3" Decision

[KillerBjt]

I just double checked the page in question in my copy of Maximum Boost, and the graph does say that a single 2.5inch exhaust is good for 450hp and dual 2 inch pipes are good for 700hp. But if you read the fine print for the graph it says "Approximate exhaust pipe flow area for specific power output". The key word here is approximate, this is a rough guideline and shouldn't be taken as fact.

[letitsnow]

I just double checked the page in question in my copy of Maximum Boost, and the graph does say that a single 2.5inch exhaust is good for 450hp and dual 2 inch pipes are good for 700hp. But if you read the fine print for the graph it says "Approximate exhaust pipe flow area for specific power output". The key word here is approximate, this is a rough guideline and shouldn't be taken as fact.

 

That sounds like maximum possible horsepower with that size pipe. As in, take a 500hp engine and make it breathe through a 2.5" pipe and it will only make around 450hp.

[HowlerMonkey]

A perfectly straight 2.5 inch pipe won't diminish performance from that turbo but, once you add the bends required to fit a car, you end up with some restriction.

 

I'm sure somebody could spend a ton of time making a perfect bends to a 2.5 inch exhaust but a 3 inch would be much more tolerant to an awkward bend that might be dictated by the layout of the car itself.