[Diy_efi] Re: "Wet" Manifold Questions

[Chris Conlon]

At 02:58 PM 5/15/02 -0700, Phil Hunter wrote:

>Running an air/fuel mixture through an intercooler is a
>seriously bad idea, when you get a backfire it could
>grenade into shrapnel.

Ya know, that was my gut reaction at first, but the original
poster was pretty clear that only fuel *beyond* that injected
by the factory ECU would have to be added pre-blower.

Say you're running 1/2 atmosphere of boost. The ECU takes
care of fuel up to atmospheric, or close to that, so you
are only adding, pre-blower, enough fuel for ~7psi of boost.
But you have 22 psi (absolute) of air in there. So in effect
the AFR in the intercooler region is about 3x what you'd
expect.

Is that too lean to be ignited? Probably. Lean burn engines
go out to what, 18:1, 22:1? You're probably way over 30:1 in
this case. Now the math changes if your boost is different, or
if the factory ECU falls short, requiring you to add more fuel.
And surely you'll be aiming for 12.x:1 or richer, which brings
you closer to an ignitable mix. But overall it seems a lot
less dangerous than draw-through with a carb, where the charge
is definitely very ignitable in the blower. If Whipple has
been doing it this way for a while, as they claim, it must be
at least somewhat safer than it sounds.

I doubt this setup is ideal with respect to detonation. The more
time you give a hot air-fuel mixture to bake, the closer you get
to preignition.

Is it feasible to inject a methanol+water mix to make up the
extra fuel? That would probably be very hard to ignite, be
good for some cooling and give a nice octane boost as well.


   Chris C.


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