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Old 04-07-2021, 06:37 PM   #29
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Originally Posted by Modernmusclecar View Post
....just dont straight pipe it and cut off the cats. Thats the real issue in regards to loud exhaust and no cats.
Glad to hear you agree with me!

I've built a few cars from the ground-up and owned a shop. Then got an engineering degree and used Ricardo Wave to design manifolds as one of my projects.

Older log-style manifolds were really bad, well worth replacing as the entire goal was to lower costs, even at the expense of fuel economy and performance. Now fuel economy is such a big deal it's going to be MUCH harder to improve on a stock manifold unless you make significant changes to the motor, like a different cam or forced induction. IMO, unless you are making those major changes I'd definitely leave it stock. In many ways the emphasis on fuel economy pushed a lot of the massive improvements we've seen in performance vehicles, as many of the things that make power also increase efficiency.

I honestly wouldn't be surprised to learn that pre-emission era vehicles used to be purposefully designed to waste fuel, then when emissions standards became a thing those requirements were often at odds with fuel economy and performance because technology wasn't developed to adequately meet emissions, so you had bodges like obstructing intake and exhaust ports in weird ways (TBI injected motors), which massively handicapped the motor. In these cases you could do mods and get significant increases in both economy and performance, and while it may not strictly meet emissions it could be argued that car ran so much better with the mods that it's well worth it.
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Old 04-07-2021, 06:39 PM   #30
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Originally Posted by TheRealJA105 View Post
Hey he said something about a catch can too and I just let that go

Just installed a dual catch can setup on my C6Z. I bought it with catted American Racing Headers already installed, but i think the LS7 manifolds and cats flowed pretty well too. (Still not as well as the LT1/LT4)
Good! I know you track your car, I'd install catch cans on it too.

An LT1 that doesn't get driven on track and is mostly stock definitely does not need one though.
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Old 04-07-2021, 07:46 PM   #31
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Originally Posted by DaveC113 View Post
Glad to hear you agree with me!

I've built a few cars from the ground-up and owned a shop. Then got an engineering degree and used Ricardo Wave to design manifolds as one of my projects.

Older log-style manifolds were really bad, well worth replacing as the entire goal was to lower costs, even at the expense of fuel economy and performance. Now fuel economy is such a big deal it's going to be MUCH harder to improve on a stock manifold unless you make significant changes to the motor, like a different cam or forced induction. IMO, unless you are making those major changes I'd definitely leave it stock. In many ways the emphasis on fuel economy pushed a lot of the massive improvements we've seen in performance vehicles, as many of the things that make power also increase efficiency.

I honestly wouldn't be surprised to learn that pre-emission era vehicles used to be purposefully designed to waste fuel, then when emissions standards became a thing those requirements were often at odds with fuel economy and performance because technology wasn't developed to adequately meet emissions, so you had bodges like obstructing intake and exhaust ports in weird ways (TBI injected motors), which massively handicapped the motor. In these cases you could do mods and get significant increases in both economy and performance, and while it may not strictly meet emissions it could be argued that car ran so much better with the mods that it's well worth it.
Ive kept all my origunal parts and they well go back if need be.If they keep concetrating on the 4 cyl with farts cans and straight pipes it will help get alot of those cars off the streets. I went catted longtubes even with the cam you can stand behind the car and smell nothing. Never got the catless thing but everyone is different.
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Old 04-07-2021, 09:15 PM   #32
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fwiw i've raced a few bolt on manifold cars. i'm sure it wasn't *just the headers but they got drug either way.
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Old 04-07-2021, 10:38 PM   #33
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So I did a test. Keep in mind all I changed was the header dimensions and these header/manifold dimensions are all from my best guess and crude measurements. If anyone has detailed exhaust measurements that would be really helpful. Also keep in mind I am not simulating cats or mufflers or exhaust pipe restriction after the manifolds, I will work on trying to simulate this though.

The modified header dimensions are from what I could measure on my Kooks 1-7/8 headers, they are not equal length but I averaged the primary length to 28 inches so probably 28 inches +/-5 inches. The simulation assumes they are equal length.

This is on a stock engine, stock cam, stock heads, stock intake, etc:
Name:  Stock Comparison.JPG
Views: 146
Size:  98.4 KB

This is on what I intend my new setup to be but I used the GMPP LT1 Hot Cam 228/236 .577/.577 110-ICL 116.5-LSA, stock LT2 intake, TSP PRC ported stock heads milled with thinner gasket (12.95:1 compression), 95mm ported TB:
Name:  Modified Comparison.JPG
Views: 148
Size:  101.4 KB

I am working on simulating the mufflers and cats, but I have to switch the solver in the software to a less accurate solver.

I also would like to add I hate headers too, with how expensive they are it just makes it worse that after you put it on you have extremely bad sound quality where you can hear ticking everywhere and exhaust pulses from up under the car along with a hacked up exhaust you can't put back to stock and an horrible smell and your car now sounds like a old 90s beat up work van with an exhaust leak and blown exhaust manifold gaskets.
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Old 04-08-2021, 07:38 AM   #34
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Originally Posted by DaveC113 View Post
Good! I know you track your car, I'd install catch cans on it too.

An LT1 that doesn't get driven on track and is mostly stock definitely does not need one though.
100%
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Old 04-08-2021, 08:10 AM   #35
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Not surprised with the results. Factory headers with cat delete pipes are a pretty good setup. Most gains I have seen are those moving to cat less headers. There was a member that picked up 19whp on a 650-700whp supercharged car coming from stock headers and cat deletes to cat less headers.

Now If you have to run cats then headers with high flow cats definitely gains over completely stock exhaust.

As mentioned by another member, cat less headers or cat delete stock headers passes emissions with Ethanol fuels. I believe most would run Ethanol fuel if it was available.

So perhaps instead of giving people shit for wanting to modify exhausts to make more power you should be asking our government why are we continuing to run all of this expensive emission equipment to clean up shit pump fuel? Clean burning fuels have been around for years that would not require catalyst to pass emissions.
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Old 04-08-2021, 09:43 AM   #36
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Quote:
Originally Posted by cmitchell17 View Post
So I did a test. Keep in mind all I changed was the header dimensions and these header/manifold dimensions are all from my best guess and crude measurements. If anyone has detailed exhaust measurements that would be really helpful. Also keep in mind I am not simulating cats or mufflers or exhaust pipe restriction after the manifolds, I will work on trying to simulate this though.

The modified header dimensions are from what I could measure on my Kooks 1-7/8 headers, they are not equal length but I averaged the primary length to 28 inches so probably 28 inches +/-5 inches. The simulation assumes they are equal length.

This is on a stock engine, stock cam, stock heads, stock intake, etc:
Attachment 1064199

This is on what I intend my new setup to be but I used the GMPP LT1 Hot Cam 228/236 .577/.577 110-ICL 116.5-LSA, stock LT2 intake, TSP PRC ported stock heads milled with thinner gasket (12.95:1 compression), 95mm ported TB:
Attachment 1064200

I am working on simulating the mufflers and cats, but I have to switch the solver in the software to a less accurate solver.

I also would like to add I hate headers too, with how expensive they are it just makes it worse that after you put it on you have extremely bad sound quality where you can hear ticking everywhere and exhaust pulses from up under the car along with a hacked up exhaust you can't put back to stock and an horrible smell and your car now sounds like a old 90s beat up work van with an exhaust leak and blown exhaust manifold gaskets.
Interesting, thanks!

The 1st sim looks pretty accurate but the 2nd... 600 hp would put it +50 whp over a ZL1, seems a little optimistic?
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Old 04-08-2021, 10:05 AM   #37
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Originally Posted by KingLT1 View Post
Not surprised with the results. Factory headers with cat delete pipes are a pretty good setup. Most gains I have seen are those moving to cat less headers. There was a member that picked up 19whp on a 650-700whp supercharged car coming from stock headers and cat deletes to cat less headers.

Now If you have to run cats then headers with high flow cats definitely gains over completely stock exhaust.

As mentioned by another member, cat less headers or cat delete stock headers passes emissions with Ethanol fuels. I believe most would run Ethanol fuel if it was available.

So perhaps instead of giving people shit for wanting to modify exhausts to make more power you should be asking our government why are we continuing to run all of this expensive emission equipment to clean up shit pump fuel? Clean burning fuels have been around for years that would not require catalyst to pass emissions.
Big battery industry and Tesla will put an end to that haha, but yeah especially the LNG, CNG, natural gas fuels. Do gooders don't want to admit that modern vehicles with modern emissions controls are virtually emissions free. Now they have to create a new "emission" that we breath out so they can continue with their ban. Of course the number varies greatly but ethanol offsets this new "emission". There's no excuse why modern engines should still be 9.5:1 compression.
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Old 04-08-2021, 10:10 AM   #38
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Interesting, thanks!

The 1st sim looks pretty accurate but the 2nd... 600 hp would put it +50 whp over a ZL1, seems a little optimistic?
This is "gross" hp and not "net" at the engine. Bigger cams have been known to produce power numbers even closer to a stock ZL1.

I have been able to get somewhat close to the stock LT1 SAE power rating, the peak power and torque is usually about 500 rpm or so lower than what it should be. Problem is I can't simulate a continuous phasing of the camshaft, but I can run it in its factory calibrated 8-10 degrees retard position at high rpms and get closer to the SAE LT1 rating, but I have to run different simulations.

If you were using Ricardo Wave that should be way more accurate than what I am using, that's a high dollar expensive industry only software?
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Old 04-08-2021, 10:46 AM   #39
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Originally Posted by cmitchell17 View Post
This is "gross" hp and not "net" at the engine. Bigger cams have been known to produce power numbers even closer to a stock ZL1.

I have been able to get somewhat close to the stock LT1 SAE power rating, the peak power and torque is usually about 500 rpm or so lower than what it should be. Problem is I can't simulate a continuous phasing of the camshaft, but I can run it in its factory calibrated 8-10 degrees retard position at high rpms and get closer to the SAE LT1 rating, but I have to run different simulations.

If you were using Ricardo Wave that should be way more accurate than what I am using, that's a high dollar expensive industry only software?

I got a grant to use Wave while in school, that was about 12 yrs ago so I can only imagine how good it is now! Even back then you could take a manifold in CAD, run fluid dynamics sim and then feed that info to Wave. Of course you can start out with a generic manifold and specify only the dimensions, then run sims to optimize it before making a CAD model, this is mostly what I did with it as I was more interested in theory than making a production part, although it was used for the school's FSAE car. It was slow going back then, every virtual experiment took the computer overnight to crunch the numbers, I bet my current computer would do it in seconds.
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Old 04-08-2021, 11:09 AM   #40
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So can someone help me understand what changing to a ported intake manifold or to the LT2 or MSD IM does? Is it similar to the Ported Throttle Body where it allows more airflow, or are there further differences?

Trying to understand what mods are cost effective and street legal, lol.
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Old 04-08-2021, 12:20 PM   #41
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Trying to understand what mods are cost effective and street legal, lol.
I think this is a key point, look at other folks' mods and see what you think.

You used to be able to build a whole new motor that would likely double the hp of the stock motor a few decades ago, these days people are spending similar money on cam, heads, etc. to get 10-20% more power, and in the process losing warranty and making the car incapable of passing emissions.

IMO, you're better off buying a ZL1 if you want more power, and if you have a ZL1 and want more power you got to think about spending 6-figures on your car and what else you could get for that cash, like a 911 Turbo S that can do the 1/4 in low 10s stock, with warranty and reasonable resale value. Your cost of ownership is likely to be less than a modded ZL1 in the end. Modifying modern cars is going down a path of diminishing returns and mostly not worth it, imo.
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Old 04-08-2021, 12:24 PM   #42
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I think this is a key point, look at other folks' mods and see what you think.

You used to be able to build a whole new motor that would likely double the hp of the stock motor a few decades ago, these days people are spending similar money on cam, heads, etc. to get 10-20% more power, and in the process losing warranty and making the car incapable of passing emissions.

IMO, you're better off buying a ZL1 if you want more power, and if you have a ZL1 and want more power you got to think about spending 6-figures on your car and what else you could get for that cash, like a 911 Turbo S that can do the 1/4 in low 10s stock, with warranty and reasonable resale value. Your cost of ownership is likely to be less than a modded ZL1 in the end. Modifying modern cars is going down a path of diminishing returns and mostly not worth it, imo.

I've definitely noticed most mods appear to be either looks/sound-based with small benefits or wildly expensive.

Why I'm keeping it somewhat simple, it is a daily driver after-all, just looking down the road for post-warranty and when I might have a second car.

Apologies, not purposefully derailing just trying to customize my car to a reasonable degree.
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