Is my quiet exhaust costing me power..? (kinda long)

[vTaKwiTHsLiCkS]

Bone stock to Exhaust Mod v1 (91 Pump/ 9bs)
Stillen DP (removes front precat and main cat)
Gutted Stock Rear Precat (before)
Modified HKS Super Drager (sp?) Exhaust

This is picture of the exhaust setup.


This is a drawing explaining how it had to be modified a bit. Lol.


I bought this car bone stock and ran a 14.1 with some boost leaks (Fontana/California Speedway @ 9pm). Then I gutted stock rear precat and threw on DP/CBE and ran a 13.6 (Fontana @ 12:15pm aka warm time during the summer). I was very happy with the results of the exhaust mods considering the differences in temperature before and after.

Currently on car now v2 (e85/DR750s)
DNP o2s
3sx Shorty DP
3sx Test Pipe
Modified HKS Super Drager
Now my car is REALLY quiet… As in I never worry about cops pulling me over though my tip is HUGE. I’ll shift at 4k all day in front of the local law enforcement with no issues. My buddy has gutted precats/dp/stock cbe and his car is louder than mine. And remember that there are some dime sized holes in the pipes near the muffler.
All this sounds fine and dandy since I daily drive my car BUT I wonder if its restricting power at WOT.

Considering.. v3
Same as v2
Modify test pipe with 60mm (2.3’) External wastegate ($140 for part)
or
Modify test pipe with 2 44mm (1.7’ each) external wastegates ($50 each)
This would essentially be a cheap boost actuated cutout. I’ve ran the motorized ones before and NOT a fan. Motors breaking.. Scraping.. I even broke one completely off when I hit a dip on the freeway and my car is not low by ANY standards (3 finger gap and I have fat fingers).

This thread got me a little excited about the external idea..
60mm ebay wastegate as a cut out 65+ whp gain - DSM Forums

Then I found out that English Racing has designed a setup for the evos similar to what I was thinking..


Curious.. I asked them IF they might have any before/after dynos..
GT35R Evo
Blue is stock catback with English Racing testpipe/wastegate combo
Red is XS Power 3’ exhaust


This mod should cost me less than $200 no matter which way I approach it. I don’t care for the additional noise but will welcome ANY additional power I can gain from this. Figured since I am a turbo car AND I'm pushing higher boost.. it will only benefit me. Or am I just tripping..? lol. Thoughts? Any constructive input will be greatly appreciated.

[vTaKwiTHsLiCkS]

Kind of surprised that I didn't get any type of feedback at all on this...

[mb3000]

Ray tested stock catback vs. open downpipe and gained something like ~16 whp, so I don't think it is going to affect you that much. If I was you I would just order that straight section of 95mm piping and get it welded in.

[vTaKwiTHsLiCkS]

Thanks for the feedback.

I believe it was like 14whp but for the discomfort of running open DP to OEM wasn't worth the gain in his opinion.

I've looked everywhere for 3.75" (95mm) piping but can't seem to find it. After someone explained the venturi effect to me, I'm considering just going 3.5" from test pipe back till where the 3" ends and merging back into the 3.75.

[Ange]

Ray tested stock catback vs. open downpipe and gained something like ~16 whp, so I don't think it is going to affect you that much. If I was you I would just order that straight section of 95mm piping and get it welded in.

totally depends on what hp he's at no?

it may not be restrictive at all for a 300hp 3s while it's probably very restrictive for a 500hp...

2,5" is adapted for stock power.

when you tune it for more hp you need 3" or more for it not to bottleneck too much.

this is how I understand it anyways..

[striker2]

totally depends on what hp he's at no?

it may not be restrictive at all for a 300hp 3s while it's probably very restrictive for a 500hp...

2,5" is adapted for stock power.

when you tune it for more hp you need 3" or more for it not to bottleneck too much.

this is how I understand it anyways..

it was already a 600AWHP car and it only gained 16WHP going from the stock catback to the open downpipe.
stock exhaust vs open down pipe at 600plus awhp - 3000GT/Stealth International Message Center

[TurboSinceBirth]

Ray also tried it again later with an open downpipe and had no power gains so he was a little unsure how much gain it was good for. The exhaust turbine is going to provide the majority of the exhaust back pressure. I think with TD04s you'll see negligible power gains with an upgraded exhaust because of how small the wheels and exhaust housing outlets are.

[UTRacerX9]

Go with 4" piping on the section before the Super Dragger. That's what I did with mine, it welds just fine to a flange that is the same size as the one on the SD. It's like a 3 or 4 ft section total. Stainless steel is fine, I looked into using titanium for weight savings but it only would have saved ~4 lbs.

EDIT: My 4 inch piping is the pink and green section of your original diagram up there. I didn't have the resonator/muffler on mine.

[vTaKwiTHsLiCkS]

So basically you ran 4" all the way back starting with the pink section..?

I'm tempted to do so but since I live in CA, I do worry about drawing attention. Figure going 3.5" starting with the pink section back and merging into the 3.75" should net me whatever gains are there and not get TOO loud.

How does your car sound with the 4"?

[UTRacerX9]

So basically you ran 4" all the way back starting with the pink section..?

I'm tempted to do so but since I live in CA, I do worry about drawing attention. Figure going 3.5" starting with the pink section back and merging into the 3.75" should net me whatever gains are there and not get TOO loud.

How does your car sound with the 4"?

Yes, 4" all the way back.

I loved the sound. It also wasn't nearly as loud as you'd think... Until you hit the throttle. It had a nice deep rumble that sounded like a V8. Because it was a deep sound, it never sounded loud to me during regular cruising, but some people who rode in it thought it droned a bit. I disagreed, my car now drones a bit between 2k and 3k, the Stealth never sounded anything like that. The only time you could really tell how loud it was, was either at WOT or going through a parking garage/tunnel, which sounded awesome IMO.