QUIKAG

Thank you, VasMan! That is good information. First time someone said they had the same sound. So, that might explain my slight perceived performance increase. Better airflow!

I don't have a CEL yet though, so wonder if it was just a small piece that broke off and it wasn't enough to trigger the light yet? I don't have any piece yet out of the exhaust. Though, as hard as I was driving it with the valves open this past Saturday at MSR, I'm sure that is all blown out onto the track.

The sound seems to change around 11:30-12:15 of the video. That is the EXACT time that I run right up to redline on a few straights of the track AND engage the PTM Mode 5 torque management a few times. So, engine near redline for a fair bit of time, plus some decent engine popping/regulating from the PTM system and KAPOW, bye, bye cats?

Good theory...I think.

VasMan

Thats my best guess considering what I experienced...

Hope to see you around at the track. I will be up in MSR-C in May.

Fizzex

As others have said it may be a result of a fractured catalyst substrate, which is a metallic substance.

However, even if a CAT has a fractured substrate you may not get a CEL as long as sufficient material remains within that particular CAT. Therefore, the rear O2 sensor on that side may not detect a loss of efficiency.

You may, however, hear a change in the exhaust sound and/or notice a rattle since there may be loose material within the CAT housing.

This is not an unheard of issue with tracked cars since the exhaust gas temp (EGT) is often much higher than when being driven on the street.

PRE-Z06

I'm betting it's cat related as youve been tracking the car a lot with traction control stepping in pulling timing like a two-step launch limiter, which isn't recommended to be used with cats as it will eventually cause them to fail.

peterpiper

It almost sounds like a spark misfire at lower RPM (not AH/TC related) at higher RPM, it sounds more "normal" (Except in a slide ). check your spark plug wires: disconnect, and reconnect to be sure they are still making a good contact. At higher RPMs they would be OK, but lower might misfire under load. I am curious what the issue is... not that many of us that track the ZR1.

QUIKAG

Okay, I have the diagnosis from the dealership:

BAD MUFFLER. They are ordering new left and right mufflers and I'll have them put on next week. haha. And I thought my LS9 was going to blow up. I'll let you guys know when they get them installed to 100% confirm the sound issue is fixed.

VasMan

So the Muffler bearings did faill

whatcop?

Good to see you figured it out

VasMan

Did they describe the failure? I would be curious if the mufflers were jammed with cat pieces....

QUIKAG

Good point, I will ask them. Though the service director I talked to (seemed like a pretty knowledgeable guy) at Classic (one of the largest Chevy dealers in the country and they service a TON of Vettes) said if it was the cat, the O2 sensors would detect a diff in airflow and trigger a CEL. He was 99% sure it wasn't a cat.

Then, when I started the car in the service bay, 3 of them were standing behind my car and they heard a rattle from the muffler area. When they checked it out later, they determine one of the mufflers was bad.

Either way, I'll ask them specifically what went wrong with the muffler, so I know for sure.

QUIKAG

Yes, I guess you were right! While it's still there this afternoon, I'm going to have them check the blinker fluid and give it an engine alignment!

3LZZ06

Make sure they re-energize the battery cables and don't forget the cabin pressure, it's suppose to be at 30 psi...

Glad to hear that the problem's resolved. Keep us posted with the results.

EyeMaster

The rattling in the muffler could be a piece of the CAT... changing the muffler is not going to fix the problem unless something is actually broken in the muffler.

PRE-Z06

A baffle could have come loose, had that happen on my TI exhaust.

Glad to hear it's nothing serious and they're covering it under warranty.

UGAZR1

Wow, glad that is resolved. I was following this thread, but didn't have anything to add other than what was already posted. Hope you have a speedy/painless experience with Classic and that fixed the problem. If nothing else, thanks for sharing the video. It was

Also, I think most of us would be interested if you created another thread with more detailed descriptions re: the sport cup tires. Haven't heard many firsthand testimonies about their usage/wear on the track

camirocz

Its on warranty. Stop guessing ,take it to the dealer they ll find the problem and fix it for you at no charge.