BaronVonBigmeat

I don't think a complete exhaust bypass would be a good idea due to the insane earsplitting noise, but I had an idea a while back for a cat bypass. You'd have your factory cat sort of kicked off to the side of a straight midpipe + resonator. You drive around with the midpipe and hopefully the resonator keeps it from being too ricey; then when you need to pass an emissions test (or when you see a cop), you divert the flow through your factory cat. No more burned out cats, and no more getting under your car to swap midpipes once a year for the smog test. Plus it would probably be cheaper than the hi-temp cats which seem to be having problems anyway.

rotarygod

I had a Q-tec cutout on my RX-7 for a very brief time. It almost made it a full day but not quite! Insanely loud if you are bypassing a muffler. If you are bypassing a cat, that's another thing. On the RX-8, you'll pick up 6 or 7 horsepower or so from a cat bypass but only 3-4 hp from bypassing the muffler. Neither of those is a feelable gain. You also can't just add them up to equal a 9-11 hp gain from bypassing both. It doesn't work that way. Save your money and spend it somewhere else.

lone_wolf025

I don't suppose you happened to have video of it with the cutout open? And may I inquire as to why you got rid of it?

In my personal opinion performance wise rotarygod is quite right put the $200 into something else. If not well it is kinda a fun toy to play with. Noisy and obnoxious when you want and stealth when you want/need it.

Theoretically (at least for piston engines I can't say for rotaries) a cutout is ideal because it allows you to retain that little bit of restriction to aid the scavenging effect on the low end (closed) and little to no restriction on the high (open). But since we're on this topic would someone knowledgable jump in and elighten me if the effect would be the same for the rotary?

BoosTED

iTrader: (2)

There is not much benefit if any from scavenging with the Renesis due to not having overlap.

Would the bypass still be earsplitting with a turbo in line before the cutout?

BoosTED

iTrader: (2)

Might have been said before but the cutoff in the pic would be better if it was closer to the bypass to the cat than in the middle like that as the exhaust would backup some before diverting through the cat.

Was the problem with that setup the lack of room?

rotarygod

It was barely tolerable for long enough to play with. It wasn't even fun. It was funny for about the first 30 seconds but after that it wore off. No video. It sounds like crap. If you want to get an idea of what it sounded like, take your entire exhaust off! I got rid of it as I had no use for it. It now lives happily on my girlfriend's dad's Camaro. A V8 with headers and a cutout is nowhere near as loud as an unmuffled rotary! It's not as annoying sounding either.

rotarygod

It doesn't matter. A closed valve will cause a higher pressure region in that closed pipe and air won't want to go down there. It doesn't matter where the valve is in the bypass pipe. The air will still behave the same at the Y and just go around it.

BoosTED

iTrader: (2)

Okay so will a turboed rotary with an exhaust bypass be unbearable?

BaronVonBigmeat

I whipped that sketch up in AutoCAD without really putting much thought into it.

I have no idea if there's actually any room for something like this, I'm too lazy and cheap to mess with any of this at the moment. If I had a turbo or an aggressive N/A tune and was burning up cats I would probably try it, but I don't have money right now so I don't have to worry about that sort of thing.

rotarygod

It would be better on a turbo as the turbo muffles somewhat but it will still be quite loud.

BoosTED

iTrader: (2)

Ahh one less thing to do

Could kick to a short muffler I suppose

It sure would sound different running out the back all quiet and then wide open going off under the car.

rotarygod

It would just be easier to use a butterfly valve that had a vacuum actuator on it rather than an electric motor. That way you can run a vacuum line to the intake manifold and have it open up at a set amount of boost. You wouldn't need to do anything. It does it for you.

BoosTED

iTrader: (2)

Like in post 7 except the valve would be in the pipe, no bypass.

maxxdamigz

iTrader: (1)

I should think the geometry of exiting a cylinder around a valve would cause some cancellation/muffling of the sound coming out of the engine. Having a redline 3k lower helps a lot too. The rotary port, though, is just wide open.

SureShot

I ran the BadlanzHPE as a header dump on my 91 turbo for almost a year before the crash.
It was the most fun & bang for the buck option on the car.
They work great on a turbo, where exhaust tune is not an issue, but pressure differential across the turbine is.
There is a video of my run through Deals Gap on Google videos. (search for "DGRR")
The turbine cuts the edgy racket from the exhaust sound, but it's still loud as hell.

On an NA renesis you would still need a tail pipe to tune the exhaust, which will make it LOUDER THAN HELL.
But, then you can close it for normal driving.
As was said, space is a big factor.

SureShot

They are most effective on turbos.

SureShot

They kill the tune on an NA.

And are LOUD AS HELL!!

cajunrx8

When I uncorked my 89 RX-7 and drove around the block, the po po was quickly cruising the neighborhood looking for the drag car!!
Hauledass to the house and put the exhaust back on.
WAY WAY too Loud!!

BigOLundh

iTrader: (1)

yes.

i've driven my turbo'd 8 with no cat a few times for some diagnostics and it was the loudest car i have ever heard in my life. Sounded completely awesome. I'm sure every cop within a few miles heard it (no understatement). My friend heard it from her house lound and clear, and she lived pretty far away from where i was doing the pulls.

Now i'm running midpipe (w/ resonator) and full 3" exhaust... i dont think doing a cut out at this point will be worht a dime for power. If i still had a stock exchaust system i would do it. Then again if you have turbo and stock cat... your cat will be dead very soon.

When i was looking into it, I was looking at the QTEC cutout rotarygod metnioned earlier. RG, did you have any problems with the cutout getting stuck in the open/closed positions after having it on for some time?

-hS

BigOLundh

iTrader: (1)

i wouldnt do that.
say you have set to open at 4lbs of boost or something. While the turbo is spooling up to that point, your exhaust will be closed and can probably cause more turbo lag than a free flowing exhaust sytem would. At that point it opens you'll get a huge surge.

Tuning for that can probably be pretty annoying.

sauceyI986

ok i thought about the idea but

theboy

is there any switches involve? photos?

anyone saw the new Lexus exhaust with pedal? suck air out.

SureShot

(Merge clean up)

SureShot

Last spring I taped my first solo run through Deals Gap.
Near the end of the 10 minute video I opened the dump all the way.
The camera mic adjusted for the loud so you can only tell by the way the other background sounds disappear.
Turbos act a little like a silencer, so the sound is not as harsh as NA.
The valve was controlled by a DPDT toggle switch on the center console.

http://video.google.com/videoplay?do...9486451&q=dgrr

The run was at low boost because of the wet road.
Also the dump was only opened slightly to make it easier to control wheel spin.
After about 7 minutes I was getting better with gear shifting & traction limits.

RXSeven1

you have no idea how LOUD a rotary can be....hehehehe, take your car off and start the car....hahaha see of you like it