toddk911

Well, there has been numerous threads about bigger exhausts and I always tell myself if I went bigger I would just go with a cutout and be done with it and mount it as far up the exhaust path as possible.

The electric ones didn't tickle my fancy and the manual un screw ones would be a pain with our cars being so low. So I had the idea of a pressure or boost activated cutout with some sort of pre determined spring on the cover that would open as the pressure/boost built so you would only have the really loud exhaust sound at WOT and/or once you start getting on the boost. And this could be adjusted to each owner's taste based on different spring rates. Some set for 1-2 psi and some for only full boost, etc. So one could retain a fully stock system and then when WOT it instantly becomes a 4", 5", 6," exhaust. lol

Well, as usual someone beat me to market. lol

I assume their results are with cat installed and the cut out is mounted pre cat. But even without it is not hard to believe a 10% gain at the wheels at 17psi and higher. As Dave L. has posted how crazy the backpressure is once you get over 12-15psi.

Dave/Mike L.: If you run with this idea I get a royalty. Or at least one for free. LOL


http://www.youtube.com/watch?v=mvCl-v_AzLE

Paulyy

It would of been better if it had no BG music to listen to the noise... and 50 hp does seem alot just for the exhaust cutoff. LR only gets a small gain, more of a spool gain from their 3" to their 4" exhaust.

dillon410021

looks very cool and i love supras

JDS968

Maybe get a "stud" mounted under the accelerator like they use for the kickdown on automatic transmission cars, and hook up a short cable or pushrod so that when you bury the pedal and it hits that stud, it opens the cutout and dumps the exhaust.

toddk911

Yea, 50 hp seems a lot, but is about 10% given the hp of the car. Also, I figure still running cat so just like our car we know how much difference cat bypass makes.

JDS: Very cool idea!!

So should the cut out be controlled with mechancial pressure by the exhaust or electronically controlled?

jerome951

My early-ish 996 has an exhaust bypass as part of the factory sport exhaust package. But in this case it's to quiet the car between 27 & 45 mph to meet Swiss noise regulations.
Circuitry is complex because it uses a speed signal to close the solenoid-driven bypass valve, but I would think something similar driven off a WOT electrical signal wouldn't be that difficult.

JDS968

I want to say electric, it would be SO simple to wire...in fact I think it would be simpler than doing it mechanically.

toddk911

Maybe a pressure sensor/Hobbs switch? X psi of boost and it opens. So it would be based on boost not rpm. That way if you happen to be in the revs but not really boosting you don't need it to open. But as boost builds, depending on each person's taste, it would then open at X pressure setting. Plus a pressure switch is easy to adjust how you want it on any given day.

Scott H

Maybe use a relay and have it activate when the DME goes into full load/WOT map? Would be a lot easier if the 951 had a WOT switch.

Edit: Another idea: If you have Zeitronix I believe they have a programmable trigger that you would be able to use and activate a relay at a % of TPS opening.

Tom M'Guinn

Here is an electric one on my car. Never dyno'd it because it was just WAY too loud inside. Mine was also a bit too low for higher speedbumps and the like, but you could probably find a way to mount it higher. The cut-out was also a bit slow to be activated on WOT, unless you are keeping it a WOT for a while. I duuno, but would think if you are picking up 50hp from a cut out, that your exhaust may be a smidge too restrictive to start with.

toddk911

I heard back from that company and they said:

"@toddk911 No, the 50whp gain was seen on a fully catless turbo-back exhaust."

So that is more impressive but like Tom says, maybe their exhaust was fairly restrictive, but if it was on a catless turbo back exhaust... ????

Tom, is that mounted off the wg tie in pipe? I'm thinking I would mount it as close to the turbo as possible so probaly right off the downpip or right before where the cat would be.

Maybe the audio is different than what you heard in person, but that sounded pretty nice to me. At least for WOT.

Duke

Don't you know the Rennlist "truth" that a 3" exhaust is "good" for at least 10.000 hp

hockeydude

why not just vent wastegate to atmosphere? Wouldn't this be quite the same?

toddk911

No, as you still have the exhaust path from the turbo all the way out the back.

JohnKoaWood

OK, how about installing a second BIG wastegate after the turbo to dump to atmosphere?

Isn't that effectively what you are pondering, a boost controlled dump valve of sufficient size to eliminate backpressure at the turbo caused by the exhaust system?? sounds like a post turbo installed waste gate to me...