exhaust, thinking of your options

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
77blue said:
After going back and forth many time I have decided to go with the OEM exhaust manifolds that came on my LS376 /480 crate engine. It's documented in multiple tests/articles that they flow exceptionally well for a mass produced OEM exhaust. Anyway, since I have a new MIG welder, chop saw, and time to practice my technique welding pipe, I've decided to do my own exhaust. Planning to do 2.5" aluminized steel unless you guys convince me I'm on the wrong track. I Like low-end torque and am not concerned with horsepower especially, so I was thinking the 2.5" was sufficient (versus 3.0"). Regarding not going stainless - I was thinking the care to car will receive will help eliminate the concern with the elements - although you guys with more experience could easily change my mind (2x price penalty).

I know it's always dangerous to ask for opinions but that's the great part about this forum is that they are worth something. Thanks in advance.

I've gone through this dozens of times so Ill point out a few things and let you think it though,
first you can ACCURATELY calculate the size of the exhaust pipe that will be required to allow the cars engine to perform well.
next, welding stainless REQUIRED back filling the pipe with shield gas , and temporary seal it while welding and TIG, is the preferred , method, and generally you'll find use of an (X) pipe helpful.
twin 2.5" should work reasonably well below about 5500 rpm, but it will become restrictive as the rpm's increase to higher rpm's, yet from what you've stated , I doubt you'll spend enough higher rpm engine time to worry about the minimal restriction.
grumpy, who makes a really good quality header for my car?

my dad always stated..

"A couple hours , well spent in doing carefully documented &,detailed research,
before.... jumping head first off the dock,
into any project,....can prevent you from wasting month's of non-productive work and a wheel barrow full of cash!!"

I get similar questions all the time, and there ARE certain brands that do have a reputation for better fit and finish on headers,
but your results are totally dependent on you doing accurate ,prior research, your asking the correct questions,
knowing exactly what cylinder heads your using,and yes better quality tends to cost more than bargain basement prices!
knowing exactly what car it will be installed into and if your dealing with a better quality manufacturer helps.
http://garage.grumpysperformance.com/index.php?threads/header-dimension-calculator.15013/
PrimaryPipeSelectionGuide.JPG

tubingsizeversusarea.png

keep in mind installing an (X) almost increases the effective cross sectional area, of the dual exhaust ,or collector cross sectional area to double what it had been behind a single header collector, by doubling the area that the exhaust flow sees, dropping the restriction to flow almost in half
http://www.superchevy.com/how-to/148-0404-best-headers-shootout/

http://www.lemonsheaders.com/

http://www.stahlheaders.com/

http://www.stainlessheaders.com/

http://stainlessworks.net/products/performance-systems/headers

http://www.burnsstainless.com/

https://www.carid.com/performance-headers.html
the links and sub-links should help
http://garage.grumpysperformance.com/index.php?threads/building-an-exhaust-system-for-your-car.1166/

http://garage.grumpysperformance.com/index.php?threads/calculating-required-exhaust-pipe-size.11552/

http://garage.grumpysperformance.com/index.php?threads/x-or-h-pipe.1503/#post-24096

http://garage.grumpysperformance.co...eld-gas-selection-for-welding.1108/#post-2185

more related links and info

http://garage.grumpysperformance.com/index.php?threads/building-custom-headers.961/

http://garage.grumpysperformance.com/index.php?threads/calculating-header-design.185/

http://garage.grumpysperformance.com/index.php?threads/what-diam-headers-do-i-need.7017/

http://garage.grumpysperformance.com/index.php?threads/exhaust-components.361/

http://garage.grumpysperformance.co...-guys-that-just-slap-on-factory-headers.3155/

http://garage.grumpysperformance.co...arder-too-find-exhaust-system-components.496/
 
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Choosing the perfect exhaust also depends on the sound you want for your car.
Not so it really requires a close look at your induction and goals. I have been reading allot on pulse tuning it goes again on building a winning combo of parts that work together. It is like choosing a cam you need to give the engine what it needs to perform at it's peak. Tuning an exhaust has allot of variables I always wondered if dimpling the curves like a golf ball on exhaust would help like it does in a head where curves are present.
 
Id doubt that (dimples) WOULD PROVIDE A USEFUL ADVANTAGE IN EXHAUST PORTS, They work in intake ports because intake ports work at far lower pressure levels, gas velocity and far lower temps,
as a piston drops in the bore outside air pressure tries to fill the resulting lower pressure void, even at sea level thats only about 14.7 psi
on the exhaust the gases are physically forced out the exhaust port by the piston on the exhaust stroke reaching TDC and the inertia of the gases expelled dragging the remainder out of the header primary, and if the cam timings correct the inrush of intake port flow reduces any significant reversion.
every test I've seen indicates a smooth surface and an exhaust tube internal size about 90% of the exhaust valve size comes close to ideal, of course theres calculators that help calculate the best length and diameter, of both intake runners and header primary and collectors and matching cam timing.

http://garage.grumpysperformance.com/index.php?threads/calculating-header-design.185/

http://www.wallaceracing.com/header_length.php

http://www.wallaceracing.com/intake-runner-length.php

http://www.wallaceracing.com/runnertorquecalc.php

http://victorylibrary.com/mopar/header-tech-c.htm

http://www.mk5cortinaestate.co.uk/calculator5.php

http://www.superchevy.com/how-to/engines-drivetrain/sucp-1104-how-to-make-custom-headers/

Cylinder-Pressure-Lrg.gif

Id also point out that cam timing matched to the exhaust scavenging has a huge effect on potential intake flow rates
exhaustpressure.jpg

EXFLOWZ4.jpg

pistonposition2a.jpg
 
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I saw the Doug thorley headers at http://4wheelonline.com and I'm thinking of getting one for my '80 corvette. Is this a good choice? I'm not looking for a huge gain but hope to get better mileage and power. I also heard good things about the Stan headers. I'm kinda stuck on this tri-y setup.
 
I like the tri-y but bigger fan of Schoenfeld Headers design I have been studying header designs allot recently. I will consult with a few people might make my own then have them ceramic coated.
 
http://beyeaheaders.com/
http://www.schoenfeldheaders.com/
Real race car headers there have a wide power band compared to drag headers that are designed for all out only. Expensive yes $800+ non coated but so are real drag headers. Again grumpy has a ton info read his links. There is allot of options bang for the buck summit ceramic coated long tubes properly sized for your application.

This is my opinion based off experience and theory
Exhaust is highly tunable and allot of hp and tq can be made but again remember any system is only as good as it's weakest link so if you choking it with junk heads only so much gains can be had. Small piece of the puzzle add in the pulse width caused from the engine pumping and then scavenging. These things can be changed by intake runner length also. There is allot of info out there to get you close and fitment plays a huge part also on a street car.

Nothing too complex we have been working on it for over a hundred years and still figuring out. If you want to really understand it better here is a great book by John B. Heywood "Internal Combustion Engine Fundamentals" it is 930 pages I have not read through the whole thing yet as it is not light reading seeing it is written for automotive engineers. It is written though where not knowing much or any thing about cars you would not be lost.
 
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