As I'm getting to know my C7, I've noticed that there's a distinct amount of afterfiring when driving casually, particularly when warming up, but even a little bit at operating temperature. 2018 GS, 17k miles, 100% stock.

Idling, my misfire counts are all zero except for a very occasional 2 or 3 count in cylinder 2. Nothing to fire a CEL, and it doesn't even cycle down to the "previous misfire count" memory. It feels like the engine is missing while at idle, which many state is normal. Bumping the idle up does not resolve this either, which was surprising.

I drive in sport almost exclusively, as I like the NPP's valving behaviour in this mode. Does the OEM tune overinject to create the pops and burbles, or is something awry?

 

perfectly normal

 

unfortunate.

 

Mine is Rear mount turbocharged and no muffler. So its even louder when it does it. Its badass. And the little chop is due to the camshaft. Wish it had just a little more bump at idle.
The C7 wasn't built completly around satisfying the 65 and over crowd. Chevy went somewhere in between. Lol

 

You're likely in the minority in that opinion, but I respect your point of view. It can be tuned to not over run if you hate it that much.

I'm pretty much asked by every client for more over run and crackles.

 

You're probably right. I've never been a fan of that fad, if I'm honest, and the insane number of kids with crackle tunes on their subarus and dodge neons and ford focuses has only made it worse. It just screams shitty tune to me -- poor fueling, timing, or both. We're not in the 200+ hp/litre territory and it's not 1993 anymore. We have very good injector and spark control available to us. There's no reason for it on an otherwise well-running engine, unless it's some emissions wizardry going on.

Thanks for coming to my TED talk.

 

I think it sounds awesome on the Corvette's and Camaro's

 

But what is the consequence of that tune if we did it that way?

 

Generally, little to none either way. If you allow the car to after fire more, you actually get a little better engine braking as a side effect. If you remove this after fire it MIGHT seem like the car doesn't engine brake as much but it would be very minor. The after firing isn't the cause of this at all, its just rather the amount of timing that can be removed to slow the engine down. As long as these changes are not extreme, the ECU will use throttle instead of timing to slow the engine down but it will react slower than if the ECU was pulling timing to slow it down.

Now there is a difference between burbles and crackles. Burbles are what is tuned into many performance cars from the factory to create that sound many of us like so much(and a few hate). Crackles is when you get loud cracks or if very extreme you get bangs or explosion sounds on decel or shifts. Moderate crackles are not typically detrimental to the car or the catalytic converters. But extreme crackles will shorten the life of the catalysts as these are explosions from the combustion event actually finishing when the exhaust valve is open and even some of it can be unignited fuel hitting the hot exhaust and lighting off. This level of cracks and bangs will destroy cats and can even cause manifold bolts to come loose over time. When you hear these extreme bangs on cars on the street, typically they have the catalysts removed and DFCO disabled.

 

I've never heard an argument of there being a difference between burble and crackle. Both are ignition events during or after the exhaust stroke. Whether it's tuned in or due to poor injector control is another concept entirely.

 

What is the benefit of either? Does not seem to be a loss either if you are tuning it out besides the engine braking.

 

I would doubt there's any perceptible difference in engine braking caused by injecting and firing during the exhaust stroke, given the valves are open. I'm sure there is on paper, and theorycrafting it out your 60 to 30 on engine braking alone might be reduced by some insignificant (but measurable) amount.

Having them not there will decrease EGTs, but for street driving there's no tangible benefit there. It'll measurably decrease the obnoxious factor, though but that's really more subjective. It definitely increases legality to have them removed. All OEM tunes that do this are technically illegal where I live, but it's seldom enforced.

I know in the 991 world the afterfiring is disabled if temperatures are outside of a specific range. Usually that only happens on a track though.

 

Short of hurting power or the car, I would want to take out the pops, after firing, crackle, burbles and gerbils. I don't care about making 1950 muscle car noise to remind myself that I have a 465 HP car. This is 2022 and we can make power with less exhaust noise. Come spring, we will get the tune in that cuts down noise without killing power or drivability if possible. So if you or anyone has any reason why it hurts, I definitely want to hear about it.

 

Understandable!

If anything I would say that removing them would (negligibly) improve the life of your exhaust components, from your exhaust valves to your catalytic converters.

 

I was looking for a tune to remove the V4 mode on top of noise reduction so the component improvements would be a additional bonus for the next guy if I get a used C9 in the future.

 

I almost forgot. I believe they can adjust the tip in so you can have the throttle body mods (insert prefered brand here) without having to modify the TB.

 

There is a difference in sound and the aggressiveness of the over run. My point was you can make it mild or extreme or eliminate it all together. I'm going to go out and make mine louder and hope I pass you on the street.

 

Hah! I'll file it in with the rest of the noise -- misfiring car (or subaru, who knows), crackle tune economy car, and now crackle tune corvettes.

 

At least I don't cover my car in stickers and instagram user names

 

oof, now that's something I'd have to properly give you a ration of **** about.