3inches or 2.5inches???;)
 

Hey guys i just want to know which is better in a exhaust setup. this of course would be on a n/a build.. when i mean better i mean it as in hp/tq gains. im planning on getting op fp and a catback all the same pipeing size. would this be a good idea? should i mix sizes on pipeing and would it have any benefit? ill appreciate the help thanks!

From what I have read before, there isn't much gain between 2.5 and 3inches for exhaust on N/A (someone check for me on this). The most gain you would get for sure is noise.

No need for 3" unless you are going FI

well according to my ruler its about 9 inches, however I am italian.

You mean 9cm?You are Italian....

Not necessarily true. http://blog.perrinperformance.com/3-...ults-and-tune/

Any independent dyno tests I wonder? Manufacturer's claims are always suspect, at least to me.

I have the perrin 3" exhaust and I love perrin products but you really need to take dyno charts published by companies for what they are, a tool to help them sell a product. Its highly unlikely a 3" exhaust makes 8 more whp than a 2.5" exhaust on a NA engine and independent testers confirm that.

To the OP: stick with a 2.5" exhaust as the increases in volume and rasp (even on the resonated systems) on the 3" exhausts is to excessive IMO.

Do you have an unbiased, third party dyno results..bigger is not always better ~3-5 whp or wtq difference may occur between pulls, 3" exhaust for NA cars (even for many FI is pointless)

Most of the time 3" becomes necessary at around 400whp levels and I highly doubt third party dyno results show otherwise

This has been debated for years and some people claim too large of an exhaust (for SC not for a turbo application of course) even hurts the low end torque.

Also some superchargers such as Rotrex kits -in general- makes a lot more power up top and lacks some low end power -as opposed to positive displacement SC s- I always thought it would be more beneficial to keep the low end TQ in expense to lose some top end (after 7200 rpm !!) and of course if it makes any difference

IF the header collector was 3" and a 3" over pipe and front pipe were included... then maybe I would agree.

But for just a catback or an exhaust that still has a bunch of restrictions, then no, just stick with 2.5".

I'm also guessing folks with the 3" have more scraping issues with the pipe goiing under the rear subframe..

No, there is no scraping issues with the 3" catback. I had rubbing issues with my JDL overpipe though which is 2.5" - doesn't fit great.

I have no independent tests although I trust Perrin is one of the more reputable shops. I understand that most manufacturers claims are usually optimistic though.

I vote for the 2.5" pipe for a NA, FR-S engine.

Why? Because that's what I bought ..... so, it must be .... "right" ....:D


humfrz

that's what i hear from guys with fi :/