Touching on Scott's comments, the factory manifold is built primarily
for emissions purposes particular catalyser light-off on cold startup.
Mazda's design is not far off from Paul's 3D tangential misload
except using a small diameter collector. They bring in short 1.75"
dia.
tubes aligned close to the top of the 2.75" collector for the
center and
rear port with the front port elbowing directly into front collector
end. Other internal emission features are the flange openings being
larger that the port opening and then round tubes butted flatly over
the rectangular flange opening to create turbulent shear vortices that
promote mixing the secondary air with the combustion gases. Even the
short tangential tubes end abruptly with no flairing or radiused
edges.
I would think that a stripped custom version of the Mazda manifold
build
for our purposes with individual plate flanges of minimal dimension
and
extra light gauge inconel tubing could be closer to 4 or 5 lbs, but
the
implications of a crack failure are much greater for an aircraft
than a
race car. If you wanted to get fancy I suppose elbowing the front
port
into a megaphone and then bringing the center and end ports into the
megaphone on a simple tangential might be a consideration if you are
willing to throw the primary length tuning out the window, as well as
the muffler chamber concept.
As for welding the tangential design utilizing long primaries and a
small diameter collector it might be more feasible to fabricate the
primaries using the flat plate design. Cutting and wrapping ring
segments with shared walls and a top plate fit flush and the wrapped
through the spiral curvature would likely only require seal welding
the
exterior joints. The shared inner walls would likely only need stitch
welding to the collector surface. In my case it would also allow
using
a rectangular 1.75" wide x 1.5" high primary for a lower profile space
consideration should that design concept be pursued.
There are more traditional tube header designs coming from Japan and
they are quite expensive and barely lighter than the Mazda
manifold. I
picked a used one a while back, a bit of a rare find here in the
states. The power gains claimed haven't been seen here in the US, but
tuning options short of complete stand alone engine management have
been
limited until recently. Some have attempted to keep the shared center
port split into separate smaller diameter primary tubes, but they have
fared no better on the dyno. 1.75" diameter seems to be the common
tube
size and the lengths seem to vary between 16" - 24", some close to
equal
length and some not. Of course they are somewhat limited to mating
with
the existing exhaust design as opposed to a completely custom system.
Unfortunately long primaries carry the cost of complexity and weight.
If the tuning gains do prove to be minimal at best, then the next best
option would appear to be the simplest, lightest design possible.
So on
the surface it appears to be a race between the simple and tuned
tangential designs.
Mark Sipe
Mark, I have read your description of how to build the tuned
tangential a couple of times and I still don't have any idea of how
to build it. That is my problem, not a reflection on your writing.
The eight to ten inch final diameter is going to be hard to live
with. I can say with confidence that you will not be able to get it
inside the S-beam engine mount. I have fit several six inch simple
tangential inside S-Beam engine mounts and there is not room for
anything larger. Also, the larger diameter would place the muffler
unacceptably close to the intake or drive it very low where it will
invade the radiator's space. The options are down to one, I'm sorry
to say, and that is the simple tangential, max diameter 6 inches and
maximum length 8.5 inches. The ones I built were 10 inches long, but
with the relocated S-beam, the muffler has had to be shortened a bit.
On the positive side, Bob Whites initial reports indicate that the
muffler may be satisfactory as far as noise suppression is
concerned. Once he goes to WOT, we will know more. Also, my muffler
which is a zero back pressure design, may deliver more power than
some of the more restrictive designs. We will soon have some real
data on h.p too. In particular I am looking forward to how Mark's p-
port breaths at 8500 rpm. The muffler/exhaust system was conceived
with the p port in mind. I got my fingers crossed...
BTW, I think the Renesis side port exhaust sucks because it
doesn't. Jerry
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