Jerry Hey wrote:
> >>
> >> Does the rotary perform best with zero exhaust back pressure? I am
> >> designing my new system and want to go for max power. I have a zero
> >> back pressure design that will also be quiet. (Did that get your
> >> attention?) But if a little restriction will help that can be done
> >> as well. If so, how much? Thanks, Jerry
> >Due to exhaust/intake overlap it is not that simple. All I
know
> >is about 32 inch exhaust pipes with 22 inch intake for 6000 RPM
> >seems to be the hot tip with no back pressure.
> >
> >Paul Lamar
> Is that 32 inches of 2" pipe before the muffler? How was this
> number derived? Is there a resource I can read? The Star Mazdas have
> a muffler which surprised me when I saw it. I can't believe it is
> about noise when it comes to race cars. Lynn? Jerry
Yes.
Well two sources. The Mazda tech papers which are on:
http://www.thecarricos.com/ACRE
in PDF format and the work that Everett Hatch did.
Here is just one graph from those tech papers.
Paul Lamar
The basic number seems to be about 10" for 1 7/8 ID tubes. Any multiple of
10". A little shorter for 2" ID tubing. Daryl Drummond builds the SCCA
Formula Mazda engines at (some secrete number here) I would say 175 HP and
they are said to be within 2 HP from best to worst. The exhaust works very
well with a very short run to the collector. Just under 10" it looks like.
Not ideal but required because of the side of the chassis is in the way. The
Sports Car Club of America (SCCA) requires that no engine produce more than
103DB at 50 feet at full throttle, thus the mufflers. The exhaust port
inserts are still in place but he may make them from aluminum as in the 12A
just to make blending a bunch easier. For my 12A I have 22" of 1 7/8" ID
tubing to a 4" long collector down to 2 1/4" then back up to 4" with a 14"
long megaphone to a 4" ID muffler 22" long and out through the passenger door
with a 4" pipe 11" long. Getting the primary pipes the same length is very
important. I use a length of old shop vac hose and keep inserting it into the
primaries as I build them up. Just fill the exhaust ports with news print and
cover with racers tape. Complete the run for one primary and jam the hose up
the primary until it stops at the port opening. Mark the hose where the
collector will attach. Build up the second tube and keep adding length by
twisting your 90's and adding short bits of tubing until the shop vac hose
fits the second primary up to the mark on the hose. I could have built one in
the length of time it took me to type this. Also the run straight out of each
port should be as long as possible before the first bend. Use .120" wall mild
steel or .063" stainless. The outside of the bends will be much thinner in
both cases.
Lynn E. Hanover
Don't forget Lynn is shifting gears at 8500 RPM.
Paul Lamar
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