[BMWM.D.]

This was talked about in several threads recently. That is, questions concerning why headers are really a very important supporting modification on this car — and why the stock manifolds are a restriction.

Well, yesterday I was cleaning out the storage area above my garage. I came across some C6 ZR1 exhaust parts that I need to sell, as well as the stock manifolds off my ZL1. For those that don’t know, the C6 Z06 and ZR1 share the same stainless steel exhaust manifolds that are a popular upgrade for LS2/LS3 cars. I personally made about 700 whp through them and a set of factory ZR1 cats.

Anyway, I decided to take a picture showing the tiny outlet of our LT1 based manifold, as well as a comparison to the ZR1 manifolds I have. I think theae pictures say a lot. I thought some of you might find this interesting. Our 2” outlets compared to the huge oval port of these.

[Vtor_ZL1]

What's needed to make ZR1 based manifold fit LT4 on ZL1 ?

[BMWM.D.]

Originally Posted by Vtor_ZL1

What's needed to make ZR1 based manifold fit LT4 on ZL1 ?

I’m not sure that’s happening. I believe the port design is different. I just wanted to illustrate how small the ports on our manifolds really are. When I saw them side by side, it was pretty eye opening.

Long tube headers are probably the best option, as I don’t think any good factory options exist. The ZR1 manifolds are a good upgrade for a base vette, but still don’t match a set of headers.

[17CamaroZL1]

So this is why no one seems to gain much by replacing the tiny and crimped pipes of the stock axle back exhaust and also why ones that replace manifolds, but keep the stock axle back don't get big gains. The entire exhaust is restricted! Thanks for that visual. Now I know I need to replace everything when it comes time to tune and do an exhaust.

[BMWM.D.]

Originally Posted by 17CamaroZL1

So this is why no one seems to gain much by replacing the tiny and crimped pipes of the stock axle back exhaust and also why ones that replace manifolds, but keep the stock axle back don't get big gains. The entire exhaust is restricted! Thanks for that visual. Now I know I need to replace everything when it comes time to tune and do an exhaust.

In my opinion the 2” outlet of the stock manifold is the biggest issue. 2.75” pipes can support a decent amount of power, though I don’t know how small the cross section is on that crushed piping. It seems to get wider, so I do wonder how much smaller it really is.

That said, exhaust diameter becomes less important as it gets further from the engine. Gasses cool and take up less space in simple terms. I’ve seen tests between 2.5” and 3” exhaust systems where the 3” midpipe picks up power, but 2.5” tail pipes after the mufflers have no negative effect. I’ve heard people say that any bottleneck in an exhaust system is the same, but that’s not really true.

[Stephen12ZL1]

https://www.dailymotion.com/video/x3vupq0

[17CamaroZL1]

Originally Posted by BMWM.D.

In my opinion the 2” outlet of the stock manifold is the biggest issue. 2.75” pipes can support a decent amount of power, though I don’t know how small the cross section is on that crushed piping. It seems to get wider, so I do wonder how much smaller it really is.

That said, exhaust diameter becomes less important as it gets further from the engine. Gasses cool and take up less space in simple terms. I’ve seen tests between 2.5” and 3” exhaust systems where the 3” midpipe picks up power, but 2.5” tail pipes after the mufflers have no negative effect. I’ve heard people say that any bottleneck in an exhaust system is the same, but that’s not really true.

I know on my car, the crushed section is actually pushed inward on top and a little on the bottom. If it was simply flattened to change the shape, there really wouldn't be any loss in area. The pipe also shrinks down again right before it enters my muffler and from a cutaway of the stock muffler I've seen, it shrinks down again inside the muffler before it can separate to exhaust through the 2 additional tips.

I definitely agree that the manifold is the biggest bottleneck. Especially being so close to the engine where the gases are hottest and only being 2"!! Even if the pipe shrinks down to 2" or even a tad less inside the muffler, it isn't going to matter until the manifold is addressed, and even then it will matter less than the 2" manifold due to the gases cooling like you said.

[WEAPON-X]

This is absolutely done for emissions to get the cat light off to happen as they have to get up to 400* within a very short time or they fail. The Camaro is a heavier car and thus more emissions challenged by the EPA. The C7 has a similar outlet as the LS9; however, this will not fit in the alpha body since there are other hard parts in the way.

[Vtor_ZL1]

You have to consider that exhaust flows in pulses, not steady stream, so at any one point, only ONE exhaust port is flowing through those 2".



That's why aftermarket = noise, not much gained in terms of power.

[BMWM.D.]

Originally Posted by Vtor_ZL1

You have to consider that exhaust flows in pulses, not steady stream, so at any one point, only ONE exhaust port is flowing through those 2".



That's why aftermarket = noise, not much gained in terms of power.

Regardless, a 2” collector isn’t ideal for power potential. And I’m not sure if you saw Ted’s dyno recently, but it looked like he gained near 40 whp near redline from a set of green catted Kooks.

[Joshinator99]

Originally Posted by Vtor_ZL1

You have to consider that exhaust flows in pulses, not steady stream, so at any one point, only ONE exhaust port is flowing through those 2".

Well, you’re technically right, BUT at 6000 RPM each header flange is seeing *50* pulses per *second*. The pulses are so rapid it’s going to hit the collector at nearly a continuous stream of air flow, even if they are technically pulsing. It’s no surprise long tube headers show such nice gains.

[17CamaroZL1]

Originally Posted by BMWM.D.

Regardless, a 2” collector isn’t ideal for power potential. And I’m not sure if you saw Ted’s dyno recently, but it looked like he gained near 40 whp near redline from a set of green catted Kooks.

Originally Posted by Joshinator99

Well, you’re technically right, BUT at 6000 RPM each header flange is seeing *50* pulses per *second*. The pulses are so rapid it’s going to hit the collector at nearly a continuous stream of air flow, even if they are technically pulsing. It’s no surprise long tube headers show such nice gains.

Agree with both of these statements

[Fraxum]

So agreed you can only make so much power with the stock manifolds. But even without LTs you can add significant power to your A10 ZL1 so that it can dive easily into the 10s and be noticeably faster than stock. At that point you are maybe 1/2 a second from getting kicked out of any drag strip without a cage.

Yea LTs would help but at a cost to me of taking my ZL1 down a few notches in street driving pleasure. But also to each their own. Owners who just want a little more fun in their ZL1 should not think LTs are required just to sharpen their ZL1 performance.

I agree LTs are a big/max build requirement. So this is good advice for anyone looking for big power just to have it or race it.

But most owners just want to enjoy the car and add some spice.

And some will maybe like or get used to the sound you get with LTs. But I say if you are considering it make sure you hear what you get with LTs, not to mention how super expensive most of them are, before you jump in. When I had LTs on the street the full time stealth setting was the norm for me and that setting sounds nowhere near as good as a stock ZL1 or SS.

[GunMetalGrey]

Originally Posted by BMWM.D.

Regardless, a 2” collector isn’t ideal for power potential. And I’m not sure if you saw Ted’s dyno recently, but it looked like he gained near 40 whp near redline from a set of green catted Kooks.

I believe it was 27whp and half a pound of boost lost.
I wish he did the test after the pulley change to see how much of a difference it made with a pulley change.
Is half a pound of boost considered much?