Does anyone ever heard of a formula for designing a tuned air box(resonant chamber) for snowmobiles...I have read alot of replies from the forum about tuners designing expansion chambers for their their specific engine...reed valves...hemi-heads, etc. but nothing about tuned air boxes, ie ram air...would'nt this work better instead of just putting on an air filter on the carb? * Thanks Al.

I think that there was a discussion last winter here about ram air. I think that the bottom line was that it doesnt work.

RE: "would'nt this work better instead of just putting on an air filter on the carb?"

Yes it would, but most people have a limited area to "build" a tuned airbox in the sled. Also a tuned airbox will have resonances at one rpm range and anti-resonances at another.
In short it will "push" an air charge at it's tuned rpm range and slow it down air charge (drop HP) out of rpm range. If it's a drag sled and hits optimum rpm and stays there, no problem. Trail use, don't know..
If you pick up a dyno I'd love to work with you on this. Chris

The formula from Kevin Cameron:
"A resonant airbox is a type of Helmholtz resonator, and there is a formula for calculating it's frequency from it's dimensions. In this formula, the frequency of the oscillator, in cycles per second, is equal to 5280 times the square root of the following quantity; area of the intake pipe's cross section, divided by (oscillator volume times intake pipe length)."

"Intake airflow through the carb and into the crankcase can also be treated with the Helmholtz formula; the crankcase volume itself is the spring, while the air in the carb, manifold, and inlet valve is the vibrating mass."



Last edited by toydoc at Sep. 10, 2002, 6:42pm

toydoc: thanks for the reply...What really sparked this thought is all the major auto companys use a tuned air plenium on their cars...ie. Ford mustangs, chevy camaros, corvettes, BMW, Yamaha etc. *The formula you addressed kinda makes sence...crankcase volume, intake volume etc., if you have some information on someone that already has crunched the numbers and the formula is the standard, that would sure help with the R @ D. *Regarding the Dyno...We'll see....I have to convince my wife I need this more than a new sled...Thanks Al.