Sent: Monday, May 10, 2004 9:33 PM
Subject: [FlyRotary] injector relocation
predictions?
Greetings,
As I mentioned before,
one of the relatively easy options for improvement will be to move the 4
injectors, and keep the current intake. As they are now, all 4 injectors
are in the TB, which is 30 inches away on the cold side of the
engine. I believe I can mount the two stock primaries back in the block,
and can probably mount the two secondaries in the intake, maybe 2 inches from
the engine.
Here's the question, do
you think this will increase power? In other words, am I losing power by
having the injectors coating the inside of the long tubing, rather than
efficiently delivering the fuel to the
engine?
Thanks,
Rusty (thinking of
draining one fuel tank, and filling it with helium to improve
climb)
Rusty, I
don't think anyone can answer that question - depends on too many
variables. You would think that even if the fuel coated your long
runners that eventually it ends up in the combustion chamber. My
(admittedly limited) experience with rotary intakes leads me to believe that
the number one, primary, uno, far outweighing all other factors, the key
element, etc. etc., is AIR FLOW!
If you DO
have the airflow then it is simple to dump in more fuel and get more
power. If you don't have the airflow in the induction system, then it
don't make no never mind how much fuel you pour into it, it won't produce more
power. Clearly, its not a simple matter to get great airflow for a
number of reason mentioned.
Tracy has
(I think) shown that airflow velocity apparently plays a major role in
producing power. His runners are 1.25 and 1.5" in dia - so clearly not
oversized. This creates higher air velocity in the runners which in turn
can cram more air into the chamber when the port opens (the momentum effect of
the moving air)
Now taking
the fact that at 6000 rpm and 100% VE a 80 CID rotary will suck approx 277 CFM
of air, so each set of runners flow approx `1/2 *277 or 138 CFM.
Assuming that the air divides between the two runners proportional to their
areas 40% for the primary and 60% for the secondary. We have .4*138 = 52
CFM and 0.6* 138 = 82 CFM
To find the
air velocity in each runner we divide the flow in each runner by the area of
that runner we find that the average velocity of air in the intake is only on
the order of 110 fps or approx 75 mph. Now most induction theory
says you want an intake velocity on the order of 300 fps, but there of course
as always a trade off. If you reduce the intake diameter in order
to achieve 300 fps in the rotary you would have to reduce the runner dia even
more and that starts to cause airflow restrictions especially at higher
rpm. On the other hand, if you enlarge the diam of the runners much
beyond what Mazda used, then the intake velocity will decrease and could
adversely affect the inertia chamber stuffing effect. At least that is
how it appears to me.
When I
combined my primary and secondary runner, I ensured that the total area of the
single tube did not exceed the combined area of both primary and secondary
tubes in the attempt to keep the airflow velocity the same as in the
Mazda.
FWIW
Ed