What exhaust diameter???

bb1boy · Post by **bb1boy** » Thu Jul 31, 2014 6:03 pm

106pete wrote:A semi decent mild steel exhaust should last 5 years and more with repairs. That'll easily out live most preludes

come on now, you know that's not true! Newkid is right, go stainless.

farlow · Post by **farlow** » Thu Jul 31, 2014 6:33 pm

I run a 2.5 system on mine but wish I'd gone for bigger. I've recently read that H22 engines will run well however big the exhaust is whereas most will start to lose power if an exhaust is to big. I'll be swapping mine for a 3" when my lude project gets back up and running.

I'm guessing that 2.5" would be big enough for most though.

Post by **GreenyUK** » Thu Jul 31, 2014 7:57 pm

I've read a few things now that H22s love bigger diameter exhausts, namely 3"
However I thought this sort of sizing territory was for turbo cars?

farlow · Post by **farlow** » Thu Jul 31, 2014 10:29 pm

If there's any chance of something smaller causing a restriction, and your looking for big power of course, then you might as well go as big as you can. I wouldn't however go any bigger than 3" as your then talking drainpipe territory and it would just be overkill.

Post by **NafemanNathan** » Thu Jul 31, 2014 11:20 pm

2.75" FTW

Post by **GreenyUK** » Fri Aug 01, 2014 7:41 am

NafemanNathan wrote:2.75" FTW

I was actually thinking that but thens it's bad enough saying it's only 3 inch don't want smaller..

Post by **NafemanNathan** » Fri Aug 01, 2014 8:31 am

GreenyUK wrote:
NafemanNathan wrote:2.75" FTW
I was actually thinking that but thens it's bad enough saying it's only 3 inch don't want smaller..

ONLY 3"?!

Don't think I've ever heard of a lude with bigger... Even turbo'd

Post by **SPYDOR** » Fri Aug 01, 2014 9:31 am

H22a8 is 2", only the Type-S and S-SPEC were 2.25" according to a post by Merlin on PreludePower a couple of years ago:

The H22a8 has the same diameter exhaust as the H22a5, both are 2.0". Its a common misconception (along with cylindrical exhaust manifold) that the H22a8 has a larger diameter exhaust. I measured my brand new OEM H22a8 exhaust and it was only 2.0". Only the Type-S and S-SPEC have 2.25" exhausts.

Does the new section fit length wise? The H22a8 has a longer downpipe and larger CAT than the H22a5, the difference in length is made up by having a shorter B-pipe on the H22a8. The length of the H22a8 exhaust sections is similar to the Type-S. The orientation of the flange will be different as well. On JDM exhausts the flange is slightly rotated in comparison with UK and Euro exhausts.

I have a full custom 2.25" system on my stock H22a8 and that has always performed very well. I have been in discussions lately with numerous exhaust specialists along with a LOT of research on this subject, as I am planning for an increase to 2.5" or possibly 3" when I get around to having my motor built.

The guys who built my original exhaust (Hayward & Scott) say they see plenty of Subaru's running 300-350bhp on 2.5" exhaust systems without any trouble and they only move to 3" exhausts above those power levels.

Solid Fabrications say a 2.5" exhaust system will be good up to around 260-270bhp at most on a Prelude H22 and Performance Autoworks said a 3" system is ideal to realize the full potential of upgraded cams and headwork on an H22. They both stated a 3" system would be better for power levels in this region and is proven to give gains across the rev range.

The theme seems to be that perhaps the higher revving Honda engines benefit from having a more free flowing system, however on the flip side is the fact that an exhaust needs to be the right size for your power levels, if you go too big you will lose the scavenging (vacuum) effect in the lower rev ranges due to lower exhaust gas velocity, which will lose you a noticeable amount of low-end and midrange power.

For my own part I will be speaking to a few more places before I decide on the ideal solution, although if Performance Autoworks recommend larger than 2.5" for the power levels I am looking at then that has to be some of the best advice you can follow.

Going by this recent advice it would seem that a 2.5" system would be best for a stock H22 around the 200bhp mark, although as I mentioned my system has always run very well with a full, custom 2.25" exhaust.

Best of luck with your decision and let us know how you get on!

nitin_s1 · Post by **nitin_s1** » Fri Aug 01, 2014 11:07 am

I'm going for 2.5"

bb1boy · Post by **bb1boy** » Fri Aug 01, 2014 11:25 am

I measured my exhaust diameter last night with a pair of digital calipers, it is 2.48"