[Z OH 6]

Originally Posted by MartinLe

There is a thread commenting on this very question. I can't find it, but the poster says that with the suitcase removed, for an aftermarket exhaust, around 150-160mph, the turbulence wants to rip the rear bumper off the car.

One person said this and no one else even the high performance shops that build these cars daily have said its not an issue. If it were a major issue then everyone with an aftermarket exhaust would be complaining about it.

[RHD ZL1]

Thank you for the Welcome and the replies guys

Originally Posted by CW3SF

FWIW, I didn’t see any reduction in mph on the backstretch of my local track after removing it. 139mph before and after.

This is good info, thanks. I am assuming the before / after 139mph was without an increase in power? (not sure if you just did an exh change only or more work all at once). As an increase in power could compensate for any drag added due to the removal of the rear OEM muffler.

Has anyone fitted an after market exh system (cat back only) and then run at the drag strip pre/post muffler removal? That would be a good indication if there is any truth to the added drag (assuming weather conditions were relatively consistent etc). Thanks.

[Gunkk]

Originally Posted by RHD ZL1

Thank you for the Welcome and the replies guys



This is good info, thanks. I am assuming the before / after 139mph was without an increase in power? (not sure if you just did an exh change only or more work all at once). As an increase in power could compensate for any drag added due to the removal of the rear OEM muffler.

Has anyone fitted an after market exh system (cat back only) and then run at the drag strip pre/post muffler removal? That would be a good indication if there is any truth to the added drag (assuming weather conditions were relatively consistent etc). Thanks.

The suitcase and crimped pipes have no effect on power (NPP valves open). That much has been proven multiple times on multiple cars on dynos (same car same dyno same day, etc.).

Unless you go catless and/or headers, catback/axleback exhaust mods do nothing to the car other than change its sound & tailpipe bling, and possibly reduce weight a bit. Any gains one would see at a drag strip would likely be due to weight differential more than anything else... but you'd be reducing weight in the worst possible spot for traction. Getting apples/apples comparos at a drag strip is pretty damn hard so maybe nothing.

But if it makes you feel better about yourself and your car and you can feel it with your butt dyno then more power to ya. Your car. Your money. Do whatcha want.

[Bangkok_ZL1]

Originally Posted by Z OH 6

People replace the suitcase muffler for weight savings and better sound. If you ever heard an AWE touring exhaust on these cars, you would certainly understand.

I totally agree, I heard it (on youtube) and it did sound freak'in awesome. Made me want to reach right into my back pocket....

[RabbitZL1]

Originally Posted by Gunkk

The suitcase and crimped pipes have no effect on power (NPP valves open). That much has been proven multiple times on multiple cars on dynos (same car same dyno same day, etc.).

Up to a certain point. I myself tested this. Gained exactly 2mph at the track. Didnt totally eliminate the muffler, only added cutouts before the muffler. The muffler itself I would say up to 900 there has no major effect on hp. I was told by Justin Keith that he lost 3mph from replacing the oem muffler with aftermarket mufflers. (air caught under the rear bumper). He goes 9.50s.

[Zl1+911]

Originally Posted by RabbitZL1

Up to a certain point. I myself tested this. Gained exactly 2mph at the track. Didnt totally eliminate the muffler, only added cutouts before the muffler. The muffler itself I would say up to 900 there has no major effect on hp. I was told by Justin Keith that he lost 3mph from replacing the oem muffler with aftermarket mufflers. (air caught under the rear bumper). He goes 9.50s.

what do you mean by cutouts? thanks

[TheRealJA105]

I bought a cheap eBay universal diffuser and some extra plastic sheet. A little cutting, riveting, and "self clearancing" from the exhaust to make it fit. It's far from pretty or perfect, but it's not a huge gap back there.

Originally Posted by Gunkk

Definitive answers? No. You'd need wind tunnel for that and AFAIK nobody has done that in a 6th gen and published the results.

Theoretically, dead air pockets under the car could increase air pressure under the car, increasing lift and reducing rear-end traction. The car has aero panels for a reason. But at anything under 150mph you're probably OK as long as you have something in place of the suitcase like a pair of A/M mufflers.
I would be more concerned about lift at high speed (1/2+ mile runs, etc.) if the car was straight piped or nascar piped, than worried about sub-100mph drag on a road course track.

Almost all road courses will be north of 100mph, probably multiple times per lap, but mostly agree with you.

Originally Posted by Zl1+911

what do you mean by cutouts? thanks

Man I thought every car guy knew what exhaust cutouts are
Maybe you know them as exhaust dumps?

[Z OH 6]

Originally Posted by Bangkok_ZL1

I totally agree, I heard it (on youtube) and it did sound freak'in awesome. Made me want to reach right into my back pocket....

Sounds better in person, I promise you no video or sound clip does it justice in real life but I find that to be the case for most exhaust videos.

[Gunkk]

Originally Posted by TheRealJA105

Almost all road courses will be north of 100mph, probably multiple times per lap, but mostly agree with you.

Oops caught me with a typo... I meant 150 but yeah I could see taking advantage of a void created by suitcase removal to reshape the rear diffuser into something that could provide a lot more downforce. Making lemanade from lemans as it were

[SFV1LE]

If you're concerned you can get a diffuser kit like this from ZL1 add ons, price is very reasonable too.

I will probably get their diffuser for stock muffler.

[RabbitZL1]

Originally Posted by Zl1+911

what do you mean by cutouts? thanks

sorry. exhaust cutouts.

[JT Camaro]

Originally Posted by LT4Greg

JT, check the Classified section of this forum and see if anyone has a take off NPP exhaust that you can get to replace the original one or install a good aftermarket axle back system. Problem solved!

I do frequently, sadly anyone up in Canada is very hard to find

Originally Posted by jaybee924

I've got a Stock ZL1 NPP muffler for sale just doesn't come with the actuators.

Would love to, but I'm sure shipping would absolutely kill the deal

[JT Camaro]

Originally Posted by TheRealJA105

I bought a cheap eBay universal diffuser and some extra plastic sheet. A little cutting, riveting, and "self clearancing" from the exhaust to make it fit. It's far from pretty or perfect, but it's not a huge gap back there.

pics?

[Checkmate1]

Someone in TX said he saw the rear bumper sag on a ZLE that consistently hit over 150mph at COTA. He strongly recommended leaving the stock suitcase muffler intact to prevent the parachuting effect.