pHEnomIC

I have a 97 z and i got it with corsa. I understand corsa is pretty high flowing and can give up to 13rwhp on a stock car. It's tone is amazing but it just wasn't loud enough for my tastes (It is designed to be quiet unless you are wot when it does get loud).

I just had a cutout put on and i was wondering if it would have any benefit to have it open hp wise or would the car be more powerful with it closed? I know it probably would only be a 1-2 rwhp difference but i was just curious

also, about how much fumes are going out the cutout is it even 50/50 out of the cutout and out the muffler or mostly out the cutout, or mostly out the muffler?

JAG05

Most would go out the cutout. Because that is the easies way for the exhaust to travel. Your muffler still has some back pressure and the cutout as none because its just wide open.. so its going to travel the way with the less back pressure.. HP I'm not sure about..

97 30TH Z

On my 99 Z28 I installed a cut-out in the middle of the I-Pipe and wanted to see what it was putting out with it colsed versus open so I ran back to back dynos expecting very little difference, but the gains were incredible. The first 2 runs I put out 295 RWHP consecutively, and then popped the plate off of the cut-out. Next 2 runs I put 321 and 323 to the ground. That's right going from closed to open I picked up 28 RWHP just by openning the cut-out. so is having your cut-out closed robbing power? In a word...Yes!

Now I may have only picked up about 10 horsepower going from no cut-out installed to cut-out installed and open, because I believe the turbulence that the closed cut-out caused, made the exhaust flow inefficient, but there was definately a gain never the less.

BTW the only other mods at the time were a lid, a pulley, and free mods.

Valkyn71

On the same subject, is their any benefit to running two 3'' cutouts on a Y-pipe as opposed to one at the end of the Y?

FlyboyZ28

How can you lose power by running a closed cutout? I'm not saying you are wrong or right. I just dont understand the turbulence thing.

redcamaroz28

7hp 9tque gain for me

TransAmGT

I normally gain about .2 ET and .25 mph if that tells ya anything!

Bersaglieri

I have actually seen people report worse times and dyno numbers with the cut-out open. Glad I have a GMMG and dont need one Works for some, others it doesnt, I'd rather save the cash and spend it on more reliable power gains.

-Dustin-

pHEnomIC

ITs cool that you can get hp gains from it. I was wondering if it created any turbulence when closed as well too. I got mine mainly for sound because corsa wasn't loud enough with dual cats in a suburban area. I didn't really get it for hp gains at all but its nice if i got some because it wasn't a terribly expensive investment.

Spinner

My cutout gains me .05 at the track, so 5hp or so?

RansZ28

they sound awesome

turbo_Z

Back when I had SLP shorties the cutout gained me about 1-1.5 mph at the track.

97 30TH Z

It's all just an assumption of mine, but I know that when I first dynoed the car, I put down 307 to the wheels and then after adding the lid (probably good for 15 RWHP by itself) and the cut-out I actually LOST 12 rwhp with the cut-out closed. Now the unfortunate thing is the 307 base and the other runs were done on different dynos, which may have affected the numbers.

My whole theory though is that once the cut-out was intalled, and closed, that it was causing turbulence/back pressure in the path of the exhaust. What use to be a straight pipe, now has a new path with the cut-out and when some of the exhaust turns to try to escape out of the cut-out, it is running into the plate and has to come back against the flow of the rest of the exhaust, causing back-pressure, thus hindering performance. Not sure if all that made sense or not, some times it's difficult writing my theories out.

brain

I gained 10 rwhp on a bone-stock LT1 (except for the cutout, lol). Power and torque increased across the board as well.

JoeliusZ28

i have no way of proving what i say, but it feels like I lose a bit of low end power (1500-3000 rpm or so) but gain some on top (3500 and up) with it open.