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
Thanks Lynn. If I interpret your description correctly, the
primaries are about generating hp and the rest of the system is
dedicated to getting the exhaust gas overboard without further
restriction. Two points that struck me as particularly relevant to
aircraft builders was the that the SCCA Formula Mazda primaries were
shorter than optimum because of frame interference. Even racers can
live with something less than optimum and if they can, so can we.
Second is your observation that the sweet spot seems to occur in
multiples of ten inches or a little less for 2" pipe. There you go
guys, 10inches, 20inches, or 30inches. If this holds true for our
6000 rpm engines, then we have some flexibility. I'm trying for 32"
but if I only get 28" so be it.
Paul, did Everett Hatch test various lengths of tube in small
increments or just the four shown in the graph?
I ordered four 45º and four 90º bends (304 x 2" x .065 ) together
with four clamps. Damn near $300.00. However, the company cut
the legs to length and is expanding some of the ends to make fit up
easier. Jerry
The only pipes I every saw on Everett's airplanes were around 32 inches
long.
That sounds expensive. Who did you order them from? RB Wagner prices
for SS .065 wall 45's are $15 each and 90's with two inch long legs are $32 each.
Paul Lamar
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