[FoundNemo]

Just curious if anyone did a before/after dyno for removing the suitcase muffler with some 2.75 or larger pipes out the back. The stock muffler inlet necks down to 2.25" at the smallest (measured with mine off the car, had flanges put on).

The piping before is 2.75", down to 2.5" around the muffler inlet, down to 2.25" inside the muffler in that order, front to back.

Highly doubt there is nothing to gain on a 650hp car breathing through dual 2.25" pipes in the back and the car certainly feels peppier with the muffler off for sure. My buddy noticed as well.

[Can'tHave2MuchHP]

There will be basically nothing to gain from an axle back only on an otherwise stock car. If you think the suitcase is restrictive, take a look at the quad set of cats the car has. By the time the exhaust makes it through that, it could care less about the muffler. If you were running a high boost, big HP setup, yeah it could eventually become a problem. But people run the stock suitcase on 800+ RWHP builds regularly. Btw, ditto for C7 ZR1s, C7 Z06s, etc. But let's say you're right, you cut the exhaust up and weld in some bigger pipes. You MIGHT pickup 5 HP.

Also, the crimped rear section has been put there for a reason by GM. Owners have cut them out and put a straight through pipe in that area and nothing changed. At the minimum, you'll want to install a full X pipe that ditches the secondaries.

[7WSM]

The exhaust systems for the performance cars of today are not that restrictive at all. I highly doubt you will see any noticable performance difference other then sound. To me, it's one of the biggest waste of money people spend their money on.

[RDBill]

I'm making 900rwhp and I recently put the stock muffler back on after having a Corsa axle back on my car (which is for sale) and actually picked up a couple of HP. Most likely due to the difference in the weather conditions between dyno days but it still picked up

[FoundNemo]

Just took the car for a spin with the muffler delete, and I have to say, I totally disagree that there is no power gain (or at least that it doesnt rev faster/more freely). I can tell for sure. To each their own, sounds awesome too!

[Scottyz]

You gonna put some kind of mufflers on it? Maybe like the track version from AWE or MBRP which basically looks like straight pipes?

[Laststandard]

Originally Posted by Can'tHave2MuchHP

Also, the crimped rear section has been put there for a reason by GM. Owners have cut them out and put a straight through pipe in that area and nothing changed. At the minimum, you'll want to install a full X pipe that ditches the secondaries.

Those crimped sections are for clearance for the x-brace the convertibles have. Mishimoto dyno tested replacing just those sections with round pipe and found 0 gains.

https://www.mishimoto.com/engineerin...he-crimp-myth/

[FoundNemo]

Originally Posted by Laststandard

Those crimped sections are for clearance for the x-brace the convertibles have. Mishimoto dyno tested replacing just those sections with round pipe and found 0 gains.

https://www.mishimoto.com/engineerin...he-crimp-myth/

Re: the crimped sections, the amount of piping diameter needed to support an SS @ 460hp (which is what they tested the crimp delete on, not a ZL1 btw) is substantially less than what is required for a 650hp ZL1. I wouldnt expect much but if the pipe isnt ovaled and is truly crimped below 2.5", i'd bet there is some power there to be had or at least throttle response and a few hp.

Rough calculation for piping diameter supporting power is the pi x radius squared x 2 (two pipes) x 112. Then divide by 2.2 to show a very rough estimate of horsepower that much pipe would typically support without restriction. If you dont believe me, cover up part of your tailpipes to only allow an area per side of 3.46" inches (2.1" diameter) and tell me your car runs great still choked off even though its at the very back. You'll be wrong, i promise.

2.1" dual pipes = 1.05" radius x 1.05 radius x 3.14 x 2 x 112 / 2.2 = 387 horsepower or so, so not much loss on a 460hp SS with drivetrain losses factored in.

2.5" dual pipes = 1.25 radius x 1.25 radius x 3.14 x 2 x 112 / 2.2 = 499 horsepower ish (plenty for SS camaro)

2.75" dual pipes calculates to about 604 horsepower (plenty for ZL1 with drivetrain losses) which is I'm sure why GM kept it close to that overall factory before the OEM muffler.

3" dual pipes (that i use now) calculates to 719 horsepower capability, but is limited to the preceding pipe at 2.75" now unrestricted through the back, which is I'm sure why I feel a nice enhancement in throttle response and a bit more power per calcs above. The OEM cats flow quite well but def would have gains if tuned right with their removal further.


The muffler inlets are not oval'd and are down to almost 2" on each side. I noticed a very nice change removing the muffler and running 3" to OEM tips (dual 2.5" from the 3") after the crimped section around 2.75". Flanged it and adding some 3" in/out x 8" long x 5" outer diameter stainless resonators to tame the bit of rasp it has. Already sounds incredible though overall! Will cerakote the setup after, all in its going to be about 750 bucks after ceramic coating, mufflers and welding and its flanged for easy removal as needed.

Mufflers incoming: https://www.amazon.com/TOTALFLOW-203...=15726991&th=1

[7WSM]

You really think you are going to feel 5-10hp at the HP these vehicles are at already? Making more noise doesn't do anything other then making more noise. There are plenty of cars making over 1000hp with the stock exhaust. Most of the exhaust companies don't even boast any dyno numbers with their exhaust anymore. For the amount of money an exhaust cost, it's not worth it for the measly hp gains if any it gives. It's all for sound.

[Vigilante375]

Only thing to gain is an increase in sound.

[CW3SF]

Originally Posted by 7WSM

You really think you are going to feel 5-10hp at the HP these vehicles are at already? Making more noise doesn't do anything other then making more noise. There are plenty of cars making over 1000hp with the stock exhaust. Most of the exhaust companies don't even boast any dyno numbers with their exhaust anymore. For the amount of money an exhaust cost, it's not worth it for the measly hp gains if any it gives. It's all for sound.

And the tips. Don’t forget the aftermarket tips are a 1000% improvement over stock.

[FoundNemo]

Originally Posted by 7WSM

You really think you are going to feel 5-10hp at the HP these vehicles are at already? Making more noise doesn't do anything other then making more noise. There are plenty of cars making over 1000hp with the stock exhaust. Most of the exhaust companies don't even boast any dyno numbers with their exhaust anymore. For the amount of money an exhaust cost, it's not worth it for the measly hp gains if any it gives. It's all for sound.

And did anyone with 1000hp have a before/after to show no gains in removing the stock muffler on their setup? If so, point the way. If you dont want to and dont believe it, dont do it. Nuff said.

[17CamaroZL1]

With the 2" collectors on the stock exhaust manifolds, replacing the 2" pipes in the back is not going to add any power. Even with headers and X pipes that increase the size to 3", many have claimed 0 gain from replacing the stock muffler. You'd think there would be, but maybe a larger size isn't needed all the way back there, as the exhaust gases cool quite substantially by the time they make it that far. Idk