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      12-07-2018, 06:19 PM   #1
amtk2007
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E92 M3 QTP Exhaust Cutout

Hello all!

I am contemplating getting a qtp exhaust cutout for my M3. For those of you who have this installed, what are the benefits and drawbacks? Is there any maintenance required for the valve. One more question: What size is our exhaust diameter. As I've scoured the threads, I see mixed results ranging from 2.5" to 3". Which size should I order?

I'd love to get everyone's opinion before making this purchase and install.

Thank you!
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      12-08-2018, 09:08 PM   #2
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I have no personal experience with the electric cutouts, but a good friend of mine used them on his LS car and they worked great until they didn't. There's not a heck of a lot you can do to help them. Grease the butterfly shaft? Its getting hit with hot exhaust probably pushing 500 degrees - the grease disappears. Theres a reason Kreis Sieg, Bomiz, and others use valves at the back box instead of the collector flange, and thats probably one of them.

If you spend time searching on any American forums you'll find that both the Quick Time cutouts as well as the DMH ones both freeze up, usually at the most inopportune time. That was enough to get me to go away from them.

("Why no officer, this car isn't modified - why would you think otherwise?")

But... the psychological advantage of a cutout is extremely valuable. Riding with that aforementioned friend - while we were on a trip to Mexico - we happened upon a guy who incidentally spoke perfect English and wanted to race. So lining up at a perfectly legal spot in a deserted area, we waited for the light to change. (No idea why there was a traffic light out in the middle of nowhere, those Mexicans are odd chaps) "Bill" revved his motor a couple of times, which was venting through Kooks long tubes into the stock exhaust, while the guy in the very built SR20 next to us was massaging his rev limiter. Once the guy was good and absorbed in the upcoming launch, "Bill" activated the cutouts.

The light changed, we both dropped the hammer. The resulting scream from Bill's car was so loud and unexpected, the other guy swerved and most likely screwed up a shift. We won. We also won the race on the way back. The guy came up and thanked Bill afterwards for a good, exhilarating race. Or at least I think he did.

I don't speak Spanish.

Now aside from the possibility of the butterfly sticking in a given position, you're also going to run the risk of losing exhaust velocity by dumping where I'm sure you'll be dumping, which is ahead of the primary cats. If you had a boosted motor, there would be a benefit. If you had a lot of cam overlap, you'd see a smaller benefit. But for an NA S65 - even FBO - you're going to lose torque. Not like we have a lot to spare, y'know?
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      12-09-2018, 02:47 AM   #3
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Quote:
Originally Posted by amtk2007 View Post
Hello all!

I am contemplating getting a qtp exhaust cutout for my M3. For those of you who have this installed, what are the benefits and drawbacks? Is there any maintenance required for the valve. One more question: What size is our exhaust diameter. As I've scoured the threads, I see mixed results ranging from 2.5" to 3". Which size should I order?

I'd love to get everyone's opinion before making this purchase and install.

Thank you!
I have the Jegs brand exhaust cutouts and i am very happy with them. I am running on the second set, as the first one came apart after 4 years.. The motors never gave out. As for maintenance, i would periodically try to tighten the bolts holding the butterfly, those bolts tend to get loose. You need to get the 3inch for our exhaust system. The 3 inch is closer to to 2.75 inches and matches perfectly. The 2.5 inch valves are way to small, they measure out around 2.25inches.
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      12-10-2018, 05:52 AM   #4
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Just get the bomiz muffler.
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