Corky's engineering goal is obviously good, since it keeps heat down, but given equal IATs, a car making 220whp at 15psi is going to be more fun to drive than a car making 220whp at 6psi or 8psi.

These two statements seem to contradict themselves. "All things being equal" meaning 2.5 bare piping vs 3.0 piping into the same brand/length muffler, the 3 inch is substantially louder. Now if you add resonators, etc, you can certainly quite a 3 inch to 2.5 levels. But then you're adding cost.

Exhaust cools the further down stream it gets. A lot of Suby guys run 3 inch DP->midpipe into a 2.5 inch axleback. There isn't a significant difference (above the dyno error) in sub 350 whp cars when switching to a 3 inch axleback. ~5 whp difference which falls well within the dynos error.

Frank

Eh? How do yo figure?

ben, the blast of torque when the turbo spools most likely.

fmowry, Mark probably is saying. a 2.5" with one muffler will be about the same noise level as a 3" with one muffler. all things being equal as in the components on and before the exhaust. the variable being the size of the exhaust piping.

The only reason I dropped the hat on a 3" was because I've heard one that isn't any "louder" than my 2.25", just deeper. Granted it used one large muffler, but if need be I'll add a cylinder muffler between the cat and diff.

Ha, ok, I suppose some could see that as "fun." Personally, I think a more usable power band is more fun ;)

I want to see what the torque curves on a dyno look like with the same engine, but one setup at 220hp @ 15psi, and one at 220hp @ 8psi. then i'll figure out which I like best.

The way I imagine it right now is that the 15psi is like that super hot chick that is showing massive clevage and gets every guy to look at her, but if you dated her she would take all your money and be a total bitch and thinks she's amazing in bed but isn't, and just wants to party and hang out with her friends instead of you.
the 8psi sounds like a decent looking girl who dresses conservatively, but you can talk intellectually to her and she happens to be a nyphomaniac and bi-curious.

i just join the rest of the guys in checking out the hot chick with massive clevage, then turn to my girlfriend and she says "damn i'd like to see her naked"

Interesting comparison.. :nuts:

The 3-inch turboback on my car does pretty much what Corky describes -- only has slight bends, and keeps the wastegate pipe separate from the main pipe for as long as possible (in this case, almost all the way into a high-flow cat).

https://www.miataturbo.net/general-miata-chat-9/pics-my-3-inch-mazdaspeed-exhaust-divorced-downpipe-10096/

Do I really need this big of a pipe for 200 rwhp? No, but it's nice headroom for when I have more $$ and build a 300 rwhp beast someday. :)

Oh and it sounds awesome. Not obnoxious but a really nice rumble.

My setup is 2.5" DP and 3" from the DP back... I decided (For the looks) to go with dual exhaust, with 3" thus meaning a larger area for exhaust gases, but my design wasn't the best and I believe I have turbulence where the pipe splits... And I also added more weight, so my $0.02 would be to stay with a single pipe...
\
miatex

Am I off in thinking that a 15psi 220whp car will build boost sooner and produce a more useable powerband than a car that won't build boost as quickly, which will produce a peaky powerband? Or is it somehow the other way around?

15psi and 220whp makes me think late spool, and a huge, quick rise in torque near late in the rev band, whereas a 6-8psi setup would more than likely build boost much earlier in the rpm band, to perhaps a lower peak torque, but much more flat. I guess you could have a quick, early spooling 15psi setup only reach 220whp, but it's be horrible inefficient/poorly tuned!

Car A has a teensy turbo that needs to be pushed to 15psi in order to make 220whp, while Car B has a bigger turbo that only needs to run at 8psi to make the same 220whp.

Car A would likely make peak torque earlier in the rev range than Car B.

Talk about pooping out in the upper rev range ;) That's no fun at all!

It wouldn't necessarily poop out in the upper RPM range. It's got a turbocharger, so boost pressure is controlled. This means, as long as you're not out of the flow range of the 'charger, torque curve should remain relatively flat.

There are so many variables, though, it's silly to make sweeping statements like these.

I've got that :bigtu:....hope she doesn't read this though :nono:

Well there's one thing to be said though. If you can make 220 hp on 6psi you probably have a much safer engine. Besides, no one is going to think you are a tuning guru if you can only make more hp by blasting the shit out of psi. If you have over 1 bar of boost you better be making at least 350 hp and in my opinion..more than that.

Well, it goes without saying that if you and your buddy have the exact same turbocharger setup, but he's making 220rwhp out of 10-12psi and you're pushing 15psi to make the same 220rwhp, either you're engine is tired, you're tuning too conservatively or he's tuning to aggressively.

It obvious that you'd want the most amount of power per PSI without sacrificing spool.

hence the 3" exhaust :rofl:

Generally, hp aside, running a higher psi at your wg will cause your turbo to spool up faster because it will reach peak efficiency faster.

So whats the verdict? 2.5 inch or 3 inch when the target is 200 - 230 hp?

btw, whats the stock exhausts diameter?

Go big or go home, Oregon or bust!