All good observations Mike. Yes, the Spintech has the open chamber
before
the baffles, kind of inherent in the design.
I hesitate to criticize the group buy effort but from my
perspective, it is
somewhat counterproductive to establish a 'standard size' for the
Spintech
and do a group buy. Aside from the excellent design, the real value
of the
Spintech is that they are willing to build whatever size, inlet -
outlet
configuration, etc, that you want. That feature is worth well over
10% in
price increase to me. Almost everyone has different requirements.
On the thickness, mine is 3 inchs thick and next time I think I
would go
thinner in an effort to keep the muffler in the turbulent boundary
layer
behind my cooling outlet. As it is, it hangs down into the clean
200+ mph
airstream a bit and costs me about 3 mph in top speed (and
cruise). Keep in
mind that mine is outside the cowl as in "Swiss muffler"
installations.
There are good and bad things about doing it this way but obviously
I think
the good things outweighed the bad.
Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com
One of the "updates" I expect to do with the RV-4 is to enlarge the very
slight tunnel under the forward fuse in order to accommodate the muffler
in
the way you describe. Right now the tunnel walls are about 2" high at
the
cowl. Since I will be doing mods to the cowling as well, making it have
more of a chin is not significantly more work. I'm undecided if I want
to
go to the scale of the 4" thick "SportsmanXL" muffler over the 2.25"
thick
"Cruiser". I also think the muffler can be made much more aerodynamic
once
we get the required volume dialed in.
Interesting that I found no 3" thick mufflers in SpinTech's lists. Was
yours a completely custom design? What are the overall HxWxL
dimensions?
I'm tending to agree with you regarding the group buy. I'm also a nut
for
flexibility. I don't want to discourage anyone from trying to save a
few
bucks and I know Brian has put a good bit of work into this deal. We
may
only be taking about a few percentage points difference in performance
between the Cruiser and the absolute optimum and a lot of guys just want
to
get flying. I may end up trying three different mufflers just for the
data. I would expect to do the trials with carbon steel units just to
save
the cash.
Mike McGee, RV-4 N996RV, O320-E2G, Hillsboro, OR
13B in gestation mode
I'm also planning to modify the cowl cooling outlet similar to what you
described Mike. Yes, my muffler was not a standard size. Going from memory
here, I think it was 9" W, 16"L, 3" D. Mine was made from 321 SS but Ed
is trying a much lower cost 304 SS which may work fine.
Tracy
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