Injector mounting in manifold.

[Ameer Antar]

I would avoid mounting injectors in the airstream before the TB for a street car b/c of the chance of igniting the mixture in the wrong place. I've heard some race cars have injectors at very long distances from the TB's, but I'm pretty sure all production cars have injectors mounted after the TB, so just in case if the mixture was to ignite due to heat or freak circumstance, the TB could just close off the air, kill the fireball and prevent it from backfiring and melting something. 

just my 2 cents.
-Ameer

----Original Message----
Date: Fri, 2 Apr 2004 15:34:10 +0100 
From: Alan Pritchard <apritchard at seaeye.com>
Subject: RE: Injector mounting in manifold.
To: 'Ben Swann' <benswann at comcast.net>, Jim Green <jeg1976 at yahoo.com>
Cc: Quattro list <quattro at audifans.com>
Message-ID: <F67A00468B77D511B80B0090278519E3922CF7 at SEAEYEPDC>
Content-Type: text/plain;	charset="iso-8859-1"

I think the big issue is producing an even mix into the airstream. An
injector in a runner has no real choice where the fuel will go, it will end
up in the correct cylinder. In the plenum area of the manifold there will be
dead spots of air, and also highly turbulent areas, and the risk of
overfuelling one cylinder while the other is leaning is just too much of a
risk. At least before the throttle body it is fairly simple to assume that
the air in a tube is all roughly moving at the same rate all across the
section of that tube. Injected fuel into this area will have time to mix
adequately. Therefore all cylinders should receive an even a/f mix from that
injector. The only risk is when fuel has time to drop out of the stream (low
rpm maybe) and settle in the manifold, then as airspeed increases that fuel
can be picked up again and fed into the cylinders, and in closed loop could
potentially appear to be too rich, lean off all the injectors and cause 1 or
many cylinders to run lean, while the other(s) are still being fed by the
fuel which has dropped from the airstream.,

Just  a few thoughts.


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