[F_Two]

Originally Posted by GunMetalGrey

Hmmm seems to be a lot of varying opinions on this, however I'm not sure that could be true if GM says this is the only mode not to race in plus I'm not sure what else would make the stock/factory suitcase muffler blow up in stealth mode like it did for DOHCVTEC on page 5 of the following thread https://www.camaro6.com/forums/showt...=527000&page=5

The guy you are talking about even says the valves open in stealth mode. He did "something like" bypassing the valves so they stayed CLOSED all the time.

Originally Posted by DOHCVTEC

no 1/4 mile pulls
everything stock except secondary cat deletes and also got rid of the crimped pipes near the muffler
not even close to passing the sound test but I don't know what the db level was on my car, i believe the track had a 95 or 96bd level limit
the muffler split at the long weld right between the tips, in front of the rear bumper, after about 20 min of lapping
and no, the valves don't stay closed even in stealth mode at wot especially above 3k rpm, at least not on my car
it looked scary but it was a pretty easy fix, just lots of parts ...
that's about all I can tell you right now
laguna pipes sound like a good idea!

[GunMetalGrey]

Originally Posted by F_Two

The guy you are talking about even says the valves open in stealth mode. He did "something like" bypassing the valves so they stayed CLOSED all the time.

He says the valves are not fully closed in stealth mode, but GT-ER said the valves stay all the way open, those are very different things. Unless DOHCVTEK had a some sort of factory problem with his suitcase muffler I'd say he is right, that the valves must not fully open or else there is no reason why this wouldn't happen to other Camaro's in every other mode and no reason for GM to say not to track the car in stealth mode.

I re-read his post and while you are correct that he made changes to the exhaust pipes before the muffler suitcase, it doesn't sound like he made any changes to the way the valves operate that I can see unless I mis-read something, which I often do!

[Indyblue98]

I would guess the reason GM says not to Track the Car in Stealth mode :
because the valves will close sooner when decelerating and stay closed longer when accelerating in stealth.
Yes they eventually open under enough throttle / back pressure , but the car is not breathing as easily as it would in track mode.

[GunMetalGrey]

Originally Posted by Indyblue98

I would guess the reason GM says not to Track the Car in Stealth mode :
because the valves will close sooner when decelerating and stay closed longer when accelerating in stealth.
Yes they eventually open under enough throttle / back pressure , but the car is not breathing as easily as it would in track mode.

That explanation works for me.

[RUQWIKR]

It also puts too much heat into the plastic housings of the NPP valves, which can start to melt them. Even open, they take a lot of heat. The Vette guys have had the AFM valves / actuators stick and fail after track sessions ran in TRACK mode. Those actuators are upstream of the mufflers in a hotter area of the exhaust, but, even not being actuated, they are exposed to a lot of heat just like the NPP ones.

[GunMetalGrey]

Originally Posted by RUQWIKR

It also puts too much heat into the plastic housings of the NPP valves, which can start to melt them. Even open, they take a lot of heat. The Vette guys have had the AFM valves / actuators stick and fail after track sessions ran in TRACK mode. Those actuators are upstream of the mufflers in a hotter area of the exhaust, but, even not being actuated, they are exposed to a lot of heat just like the NPP ones.

Good to know!

[Johnjan]

Any kind of advertised dB level can be very misleading since there are so many variables in the measuring process. Distance, meter height, angle, humidity, etc. There is no "industry standard" so trying to compare numbers can be pretty meaningless.

Industry Standard:
SAE Engine Sound Level Measurement Procedure(STABILIZED May 2014) J1074_201405

This SAE Recommended Practice sets forth the equipment, environment, and test procedures to be used in measuring sound levels of engines. The purpose is to provide a uniform method of measuring the maximum acoustical radiation from the exterior surfaces of an engine under representative engine operating conditions. The measured sound levels will be useful in development of engines, comparison of engines, and installation of engines in various applications.

[Rodan]

Originally Posted by Johnjan

Industry Standard:
SAE Engine Sound Level Measurement Procedure(STABILIZED May 2014) J1074_201405

This SAE Recommended Practice sets forth the equipment, environment, and test procedures to be used in measuring sound levels of engines. The purpose is to provide a uniform method of measuring the maximum acoustical radiation from the exterior surfaces of an engine under representative engine operating conditions. The measured sound levels will be useful in development of engines, comparison of engines, and installation of engines in various applications.

I was referring to aftermarket exhausts, but thanks for the tip.

[BMWM.D.]

Originally Posted by GunMetalGrey

He says the valves are not fully closed in stealth mode, but GT-ER said the valves stay all the way open, those are very different things. Unless DOHCVTEK had a some sort of factory problem with his suitcase muffler I'd say he is right, that the valves must not fully open or else there is no reason why this wouldn't happen to other Camaro's in every other mode and no reason for GM to say not to track the car in stealth mode.

I re-read his post and while you are correct that he made changes to the exhaust pipes before the muffler suitcase, it doesn't sound like he made any changes to the way the valves operate that I can see unless I mis-read something, which I often do!

I believe he did something to keep the valves closed, but wanted to be quiet about it.

That said, I use Stealth mode to sneak out of my developement, and use my controller to go to ‘fuse pulled’ when I crest the hill a few hundred yards away. I never drive in stealth otherwise. A few times I’ve had people fly up behind me at 60+ mph while I’m creeping away, and I’ve needed to accelerate harder to get up to speed. I’ve had the valves open a few times like this. Seems to be a combination of rpm and throttle. It’s super obvious when they open with my headers.

[Johnjan]

And I was wrong about the previous SAE standard that I referenced. This should be more appropriate for the discussion. And for those that live in Cali, you need of be aware of this if you get pulled over for perceived excessive noise...

Measurement of Light Vehicle Exhaust Sound Level Under Stationary Conditions J1169_199805

This SAE Standard establishes the test procedure, environment, and instrumentation to be used for measuring the exhaust sound level of passenger cars, multipurpose vehicles, and light trucks under stationary conditions. Measurements are taken under steady-state conditions. In this respect, this procedure differs from ISO 5130 which includes measurements under the dynamic conditions of an engine deceleration. This sound level measurement procedure has been developed as a guide for governmental agencies establishing in-service sound level limitations and enforcement measurement procedures. It is directed at the assessment of vehicle exhaust noise and is not intended to determine maximum vehicle sound levels.

[nighttowl]

Originally Posted by GunMetalGrey

Does anyone know what Db level the stock/factory exhaust system is in Tour Mode at WOT?

The owners manual doesn't say anything about not racing in this mode, only stealth mode, so I'm hoping it's under 95Db

Stealth mode??

Is this something only the standard ZL1's have?
My car has only tour, sport, track and snow, plus the PTM modes.

[BMWM.D.]

Originally Posted by nighttowl

Stealth mode??

Is this something only the standard ZL1's have?
My car has only tour, sport, track and snow, plus the PTM modes.

All the ZL1s have it. You need to select it in the MyLink menu where you can set everything individually. It’s not part of the drive modes as far as I know. Maybe it’s active in snow & ice, but I’m not totally sure.

[dlct3]

HELP!

I'm in the same boat. Planning to attend NCM in Bowling Green Kentucky for a 2 day event in April. Trying to figure out a plan for their 103 DBA limit. Currently running 1 7/8' ARH headers, NON Catted, & the 3" ARH long system into stock NPP. DB measurement I'm told is at 50' from track edge. Pulley, intake, tune, etc.. 675 WHP range.

Can anyone chime in on what this power combo produced for DB at other tracks, etc? I'm worried just a Laguna pipe on the outside free flowing side will not dampen or redirect enough to pass. I also saw where restricting the exhaust diverter to closed was catastrophic.

Another Question.. which is better for lowering DB? 2.5" or 3" laguna pipe diameters?

[GunMetalGrey]

I put 2 detachable 3" in / 3" out Flowmaster Super 50 series on my car (it does not have LT Headers yet) so I'd get under the 95 Db max sound level of my local track and I was way under!
79Db according to the tracks measurements.
The app I downloaded for my phone said 89-92Db
When listening by ear, it's barely louder at WOT than it is at idle/start up.

Who knows how accurate the App is and there is obviously a lot of variables and different ways to measure sound level. I think the main point is the Flow master Super 50 series are the largest mufflers I could find that would fit without having to be modified. I think they'd keep the car under 95db even with LT headers and EASILY under 103db

I don't recommend them for the street because they drone and don't go loud enough for my tastes, but that's personal preference.