Can anyone give an informed opinion about injector diffusers? I'm

talking about the little plastic inserts that go in the injector holes- the
injectors spray fuel on and through them. Are they necessary for our
application? Why does Mazda(and presumably other manufactures) have them? Is
it for better fuel atomization at low  airflow rates? It seems that they
add a bit of restriction to the airflow in the manifold, and might be
unnecessary in our application, if, as Paul says " all the fuel eventually
ends up in the combustion chamber".

Anyone?
Brian Trubee

Well atomization as they call it is very important. Recent automotive

industry

test indicates that improved BSFC can be had by increasing the EFI fuel
pressure. The drawback is the injectors wear out faster as I recall.

If the injectors are right near the rotor housing there is precious
little time for this atomization to happen. The inserts cannot hurt
if used on the other end of the intake tube and I don't think they
hurt where they are now. I suspect they help the BSFC or Mazda would
not use them. They were mentioned and briefly discussed in SAE paper
841017 Recent Tech.... which should be on Todd Carricos site for
downloading.

www.thecarricos.com/ACRE/


The effect may be less pronounced on the RX8 as raw fuel is recycled.

Paul Lamar

John Gibbons wrote:

Brian, Paul and all,

    My experience with the diffusers was after I put my 13B back into my 86
RX7. After the first few weeks the car would not idle. I traced it to the
injector seals and the problem went away when I replaced the seals. Not for
long though. I finally realised I had missed putting the diffusers in the
new housings so the seals were able to float and would twist a little under
very low MP. Once they had twisted the manifold would leak again. When the
seals were effective though the car performed in the same manner as it does
now with the diffusers and seals in as they should be. There must be some
difference or Mazda wouldn't bother with them, but from a driving stand
point I couldn't notice one.

    I read the post on the insurance issue with great interest, although it
is not effecting me directly yet, it is the hot topic on the Christavia
group as one builder in Ca. is not able to get insurance for his Ford V-6
aircraft. As he hasn't got insurance on it, he is not allowed to move the
project into his hangar at the airport from his basement workshop for final
assembly. There have been a few e-mails fired off to EAA and AOPA with
polite but so far unproductive responses. As a guess I would figure 40 % of
the group would fall into the conversion category. Most of the Glastars I
have flown or am familiar with are conversions also. I have a NSI Glastar to
flight test when the weather improves a little. It will be interesting to
see how it performs. I know it won't compare to a rotary  one Paul but I bet
it will be better than the Lyco I did last.

John

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