[RHD ZL1]

Hi All,

Proud owner of a 2019 ZL1 all the way from down under Australia.

Has anyone here have a definite answer if removing the factory rear muffler (to be replaced with aftermarket exh system) has any effect on the aero of our cars? Removing the suitcase style rear muffler leaves a large void under the back of the car that apparently then allows air to collect up against the rear bar and add drag rather than the air passing under the OEM rear muffler and preventing added drag from occurring. Has anyone any info on this?

Thanks.

[bcasurvey1]

i havent heard anything, your speaking of like a tailgate in a pickup truck? if you are worried about it you could always add a sheet of carbon fiber or aluminum under it to keep the air moving. js

[HCI2000SS]

I actually posted this same question a while back, and the answers I got were basically the same. The consensus was that it wouldn't make any measurable difference on your average type street car.

[hawk02]

As HCI2000SS points out, there was a similar thread on this subject a while back.

https://www.camaro6.com/forums/showt...light=diffuser

If you're tracking your ZL1 and trying to eke out every ounce of performance, having a big gap underneath the car in front of the rear diffuser could have some effect on lap times. The effect of that same gap on the street is probably negligible.

[Z OH 6]

Vengeance Racing told me that they've never heard of any issues with this from their customer using aftermarket exhaust that race their cars.

[Gunkk]

Originally Posted by RHD ZL1

Hi All,

Proud owner of a 2019 ZL1 all the way from down under Australia.

Has anyone here have a definite answer if removing the factory rear muffler (to be replaced with aftermarket exh system) has any effect on the aero of our cars? Removing the suitcase style rear muffler leaves a large void under the back of the car that apparently then allows air to collect up against the rear bar and add drag rather than the air passing under the OEM rear muffler and preventing added drag from occurring. Has anyone any info on this?

Thanks.

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.

[DaveC113]

It can't be good. If it were my car I'd replicate the suitcase with a sheet of aluminum, but FWIW, I can't see replacing the suitcase doing you any good except costing you money and making the car louder, which it doesn't need.

Those saying it doesn't matter are surely wrong. There is a reason why racecars spend so much effort on aero, including under the car, and they'd NEVER leave a gap like that!

It could certainly have an effect on hwy mpg and maximum speeds achieved on straights.

[JT Camaro]

Sadly, I bought my car used and the previous guy had done a muffler delete. I've been looking for a solution ever since to block out the air. There is essentially a big parachute at the rear of the car now

[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!

[CW3SF]

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

[jaybee924]

Originally Posted by JT Camaro

Sadly, I bought my car used and the previous guy had done a muffler delete. I've been looking for a solution ever since to block out the air. There is essentially a big parachute at the rear of the car now

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

[MartinLe]

Originally Posted by RHD ZL1

Hi All,

Proud owner of a 2019 ZL1 all the way from down under Australia.

Has anyone here have a definite answer if removing the factory rear muffler (to be replaced with aftermarket exh system) has any effect on the aero of our cars? Removing the suitcase style rear muffler leaves a large void under the back of the car that apparently then allows air to collect up against the rear bar and add drag rather than the air passing under the OEM rear muffler and preventing added drag from occurring. Has anyone any info on this?

Thanks.

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.

[arpad_m]

I'll just paint the suitcase flat black come next March, maybe the inside of the tips, too. Sure beats the cost of a Borla or a Corsa, and the sound of the factory NPP is fairly good to me. It also "matured" a bit after a while, with less rasp and more low rumble.

[Z OH 6]

Originally Posted by DaveC113

It can't be good. If it were my car I'd replicate the suitcase with a sheet of aluminum, but FWIW, I can't see replacing the suitcase doing you any good except costing you money and making the car louder, which it doesn't need.

Those saying it doesn't matter are surely wrong. There is a reason why racecars spend so much effort on aero, including under the car, and they'd NEVER leave a gap like that!

It could certainly have an effect on hwy mpg and maximum speeds achieved on straights.

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.