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Message
Hi
Guys,
I'd have to endorse what Rusty has said. His expereience
parallels mine. (What did Einstein say about insanity? - "Doing the same
thing over and over agian and expecting different
results"??)
So take a leaf
out of Mazda's book. They have STAGED injectors, and for
good
reason.. They have two on the centre housing for idle and low
speed
throttle response (complete with deflector plates!). The
secondary
injectors are placed further away. They only operate at high
RPM and large
throttle openings. If you operate them without sufficient
air flow, you
will get ALL sorts of mixture & throttle response
problems, fuel reversion
etc.
On race cars, we
now almost ALWAYS run the injectors below the throttle plates
.
Most commercially available throttle bodies (see pic) do the
same. That
being said, there ARE some advantages in running the injectors
in the
trumpet mouths, BUT there are downsides as well, which have
already
been touched on here by various people.
As with all
things, be careful when trying to re-invent the wheel or
"improve" on
what the manufacturers do. Too many of the mods done on
experimental
aircraft engines, including those suggested at that "other
place" are
either un-necessary. or CAN be dangerous if not applied with a
good
dose of understanding. Running injectors in the trumpet mouths is
one
of those instances. So Beware! There ARE advantages,
but there is also a
downside.
That being said, I remember
working on a BMW race car some years ago. They
had TWO sets of
injectors. One set was close to the engine for good low
speed and
part-throttle throttle response. There were a SECOND set of
STAGED
injectors pointing directly into the Carbon Fibre trumpets, and
only
operated at more or less WOT and high RPM. Sorry, no pix -
it was a LONG
time ago.
Closer to home, I have done a similar
thing with a turbo Nissan 180 SX
acouple of years ago. TWO sets of
injectors, one set in the stock position
close to the head, and a
second set upstream of the throttle plates. The
second set are
staged, and only come in when the MAP is over 1 Bar, and
the revs
are over 4,500 RPM. Notice that the secondary set are pointing
striaght
along the inlet runners. The throttle body is underneath the inner
fuel
rail - if you look carefully, you will see the end of the
brass
throttle shaft.
So moral of the story is that if you want good
throtle response (and DON'T
kid yourself that you DON'T - listen to what
Rusty has to say), then be
really careful how you place your
injectors, and how you stage them. If
they are NOT staged,
then they MUST be ALL on the engine side of the
throttle body (ies),
and not TOO far away from the engine.
Anyhow*, that's my little
velvet bag of uncultured pearls for
today.
Cheers,
Leon
----- Original Message -----
Sent: Tuesday, June 21, 2005 8:56
AM
Subject: [FlyRotary] Re: Fuel Injector
Position
Rusty, where were the butterflies located? Jerry
Hi
Jerry,
I was using
a TWM throttle body, with 4 injector pockets, so the injectors, and
butterflies were both at about 30 inches from the ports. It's my
understanding that the issue is with the injector distance, not the
butterflies.
It would be
interesting to try putting only the secondaries at a distance, and make the
staging point as high as you can. This would give you a nice cooling of
the intake charge under full throttle ops, but maybe (key word) not hurt
throttle response that much. This could be particularly useful for a
turbo without an intercooler.
FWIW, the
cooling of the runners was significant. During my initial runs (in the
summer), I shut the engine down a couple times to go look for leaks, since I
was getting water drops on my canopy with the cowling off. Turns out, it
was condensation on the intake runners that was blowing off, and they were
cold to the touch.
Cheers,
Rusty
(where the heck is Ed when you need him)
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