Bill, please credit the people you are quoting by including their names
at the end of their quote. Also it helps the new people on here if you
quote the entire message.
People have had problems in the past with all plastic runners.
Heat soak after a run can be a problem. Some have been known to burst
when the inevitable back fire happens. I think Tracy experienced that
problem as I recall.
Paul Lamar
What is really important is to choose the right composite for the
application. If you use polyester resin and glass to build an intake
manifold, you can expect all of the shortcomings and resultant problems you
mention. If, however, you use carbon fiber (mix) with high-temperature
epoxy, normal engine compartment temperatures and modest backfiring should
not be a serious issue.
The epoxy carbon fiber composite is as strong as steel (but weighs
much less.) If you mix in some Kevlar or glass, it also has good impact
resistance.
The epoxy chosen sets the maximum allowable temperature for the
finished composite. Typical epoxy has a service temperature of about 200 F.
It is not hard to find epoxy with a service temperature of over 400 F. (If
you are willing to pay the price, you can buy epoxy that will take 600 F.)
Of course, you pay a lot more for high-temperature epoxy and
carbon fiber than you would for polyester fiberglass. (About ten times
more.) The cost of the materials is a large fraction of my projected
(PIOMA) cost of $900.
It would be wise to put a heat shield between the intake and the
exhaust manifolds to keep the heat transfer under control, regardless of
what you make the manifold out of.
Bill Dube'
Paul Lamar wrote: (my responses inserted)
Carbon composite is only stronger than steel if it is filament wound.
If injection molded it is only a little bit stronger than the Epoxy resin.
http://techreports.larc.nasa.gov/ltrs/PDF/NASA-96-tm110286.pdf
The above are test results for high-quality carbon fiber composite
lay-up using pre-preg. Minimum ultimate longitudinal tensile strength =
242,000 psi.
No matter what direction or nature of the stress, pre-preg carbon
fiber will beat out welded aluminum that you have not heat-treated. (~9,000
psi)
Epoxy Resin is in the ball park of 5,000 psi while steel is 60,000 psi
to 300,000 psi. Furthermore Epoxy burns.
If you use the be$t high-temperature epoxy re$in, carbon fiber
composite will withstand 600 F. Epoxy designed for 400 F or 500 F will work
just fine, however
A heat shield does not help much in a heat soak situation.
If the heat soak goes over 500 F for any substantial length of
time, the cowling has dissolved into a puddle long ago. The injectors would
have melted. The connectors on all the wiring would be history. All the
water would boil out of the cooling system.
If you use the correct resin, then the intake will have no trouble
with high temperatures. Other things under the cowl will fail first.
If you use hardware store epoxy (or boat epoxy,) you will have all
the problems you allude to. It won't take more than 200 F. The solution is
to not use boat epoxy. :^)
I am with Ian on this. Play it safe. Use the stock RX8 aluminum lower
manifold, cut it off, weld on some tubes and weld on a four inch square
aluminum extrusion for a plenum and call it a day. See the
second, third and fourth pictures.
A "cut and paste" aluminum manifold might be a short-cut for me or
you, but it doesn't really help anyone else. My goal is to come up with a
solution that works for me AND makes life simpler for other folks. As I
said in an earlier post, it would be much easier for me to make a one-off
manifold just for myself. Even if it worked perfectly, it would be little
help the rest of the rotor-heads.
Also the carbon fiber manifold would weigh much, much less than a
"cut and paste" aluminum manifold. The composite manifold should weigh 4
pounds at most. The cut-and-paste aluminum manifold would weigh about 15
pounds, likely even more.
Bill Dube'
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Our current P-port manifold and slide throttle weighs about 3 pounds.
2 pounds for the slide throttle and about 1 pound for two
2 inch dia. .065 wall aluminum runners about 16 inches long.
Looking forward to seeing your hand layed up, vacumm bagged, autoclave cured
epoxy pre preg intake manifold. Are you sure it will only cost
$900 ? :)
Paul Lamar
BTW Tom what is the status of my order?
Paul Lamar
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