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Resonance tuning in exhaust.

Old 07-11-2008, 11:03 PM
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Default Resonance tuning in exhaust.

I have yet to see any real discussion on this so I'd like to start one. Exhaust tuning seems to be just about as important, if not more than intake tuning. How does one go about tuning the resonances of the exhaust to coinside with resonances of the intake? I know Helmholtz resonances are the ones typically used for intake design but can the same be used for exhaust, despite the fact that the pressure wave it moving away from the motor?

I'm working on a couple projects up at my shop and it would be nice to know the why of header tuning instead of just plugging numbers into the calculator on headerdesign.com
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Old 07-13-2008, 07:34 PM
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in exhaust tuning you are trying to tune for the vacuum wave to arrive while the exhaust valve is still open,using velocity of gases for the exhaust and the speed of sound for the returning pressure wave you can calculate the correct length for the header. i hope someone with a little more experiance will chime in , rather than my arm chair engineering.
o and heres a link i found interesting
http://www.burnsstainless.com/TechAr...ry/theory.html
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Old 07-13-2008, 08:46 PM
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For those interested there is a program called PipeMax. You plug in the specifications of your motor and it will tell your what size header you should have and how long the primary pipes. Then it will tell you what diameter collector you should have and how long.

Also you need to research exhaust termination boxes. They act like and open collector but the outlet is run through the proper size exhaust pipe and muffler. If done correctly you are talking a 30 or so horsepower gain depending on your combination.

I plan on doing this on my 3rd gen.
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Old 07-13-2008, 10:49 PM
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Intake ramming or tuning gives peaks at certain rpms and troughs or "holes" at other rpms between the peaks. Exhaust tuning does basically the same thing.

You coud use exhaust tuning to increase the peaks of the intake tuning if you were running in a narrow rpm band like at Daytona, OR you could use the exhaust tuning to fill in the troughs or holes in the intake tuning to have a smooth torque/hp curvwe for an engine that has to work thru an rpm band like a street or drag engine.

Some folks do this, some do not. Some win, some do not.
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Old 07-14-2008, 05:23 PM
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I've researched resonance termination boxes in the past, they will definately be put into use on these projects. I'm attempting to get the peaks of the exhaust to line up with the valleys caused by the intake for a decent overall smooth powerband like Old SStroker mentioned.

I'm quite familiar with Pipemax, its great software but I'm more interested in being able to do the math myself instead of just being an "idiot" and plugging numbers into software. I want to know the why not just the how of exhaust tuning.

So i understand that you want the exhaust pulse of the cylinder fired before to reach the collector as the the exhaust valve for the current cylinder opens. IE, if it were a 4 cylinder engine with the firing order 1-3-4-2 you'd want the exhaust pulse from #1 to reach the collector as the exhaust valve for #3 opens.

Does helmholtz not apply to this? I realize the pressure wave is moving away from the motor but its still in a tube of tuned length and volume. I would personally believe (correct me if I'm wrong) that since helmholtz goes from plenum opening to back of intake valve you could use the similar tuning (and the same math) to go from the back of the exhaust valve to the point that the tube meets the collector.
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Old 07-14-2008, 06:01 PM
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I don't think the Helmholtz equations are going to work, because of the much higher and more variable pressures and temperatures at work. I'm personally not aware of any simple math based on the underlying physics, but there are rule-of-thumb equations like those developed by Bell.

I'd recommend downloading the Dynomation user's manual from the Pro Racing Sim web site, and reading the section entitled "Wave Dynamic Analysis". This has the Bell formulas, and gives a good overview of exhaust tuning function as well. Incidentally, this manual agrees with David Vizard's observation that broad variations in primary and collector length are not that important in non-competition applications ...
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Old 07-15-2008, 01:36 PM
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David Vizard does believe in exhaust termination boxes. For them to work correctly they have to be of the proper size. That is each back of cylinders of a V8 motor most have a cubic inch equal to at a minimum of 8 times the volume of one cylinder.

The exhaust collector should be of the proper diameter and length for maximum gains. A program such as PipeMax can help you arrive at what is the proper diameter and length of primary pipe for you particular motor combination.
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