make 1 for a motorcycle dyno?iethe with a 55 gal drum or 15 gal.how many baffles would work to reduce the sound?copuld i make stackable stages inside the drum to improve the db reduction?
thanks for any help,ideas!i am also looking into used semi truck mufflers.

Dig a pit behind your shop/garage and put them in
the ground.... also get the inlet tube/pipe in the
ground as soon as possible to aid in cooling.... the
cooler the exhaust is the easier it is to control...
you wont need much in the line of baffles if you can
get it cooled

Thanks MR P BODY.i understand you concept.i learned a little from this post i found.
http://www.eng-tips.com/viewthread.cfm?qid=164042&page=1
i am looking for a mobile device for reasons that the dyno may get moved to another location.

I would use the largest barrel you can find. You essentially have a low pass acoustical filter, the bigger the volume, the lower the frequencies passed.

http://en.wikibooks.org/wiki/Acoustics/Filter_Design_and_Implementation