What's the purpose of the crimped exhaust?
 

Al,

What function is provided by the crimps in the section of exhaust pipe near the rear differential?

Thank you!

(I’m not certain if this exists on all trims. It is at least present on the SS and ZL1.)

Attachment 917905

It is crimped to allow a common pet number between the coupes and the convertibles. The convertibles have a brace there which the coupes do not have.

It does not materially impact power, though it does impact sound.

Source: I asked a GM engineer who worked on the development of the car.

Thanks! That sounds reasonable. I suppose I was looking for a slightly more official answer, but this will suffice.

Does anybody have a picture of this brace that the exhaust must avoid? I tried googling, but I didn't find an actual picture.

How does this not affect power? Does it have the same total inside area?

At one time there was an issue with some aftermarket exhaust systems that touched the cross member and slight rattle caused the appearance of knock which would retard timing and pull power.
Not something you want to deal with.

Crimps have definitely been shown as a non-issue as far as power is concerned.

One company ran one test a couple of years ago and saw no gain removing them. Another company recently shows a gain removing them. I can tell you removing them along with the afm valves was my first mod.

I would estimate they are crushed to 60% of their original cross section.

Over the entire length of exhaust pipe, you're only losing a few hp from the pipes themselves. So excluding the mufflers, excluding the cats. Just the round pipes themselves. And thats on roughly a 10 foot length.

That crushed area is what ... 4, maybe 6 inches in length? So no more than about 5% of the total length. Now, its still fairly close to the same overall area. Maybe it increases restriction in that one little section by 20%.

To make the math simple, lets say there was maybe 10 hp lost along the total length of pipe from the engine to the tips. 1 hp/foot. This little 6 inch section, if it were full diameter, would then be robbing you of a whole 1/2 a horsepower. But since its flattened on the one side making it a bit more restrictive its now like 0.6 hp. A difference of 0.1 hp from a 'perfect' pipe. Oh wait, there's two parallel sides ... so its total for the system of 0.2 hp. Give or take. You're not going to notice that tiny of a difference on a dyno, let alone out in the world.

I'm just guestimating my numbers here. But even if I'm way off, its still hard to get it to work out to more than about 1 hp extra compared to a perfect pair of pipes.

here is what holly is claiming with their crush pipe delete kit.

https://images.holley.com/705013126rhkr_dyno.jpg

Those dyno runs were 5 months apart. I'm not saying I don't believe it... well... yeah I am. I don't believe it.

like I said above one place says 0 gain. everyone believes it and preaches it. another place says 12hp. for the cost to get rid of it was a no brainer for me. most people considering this mod will or have all ready done other mods. it would be great to see a same day test.

To me, its a no brainer to not trust a company's data when they're blatantly trying to sell you something based on that data. Thats what 3rd party testing is for.

I agree. it would be great if someone did some back to back tests. this question comes up at least once a month, it would be great to have a little more data on it.

Sorry, but your “theory” is 100% patently false. By your “theory” If there was 1” of exhaust length that was only 1mm diameter it would not effect performance much if at all because the length of the restriction is so short. That’s just not true.

:popcorn: