Intake manifold cross over tube
Sent: Saturday, May 05, 2007 1:24 PM
Subject: Re: [Fot] Intake Manifold Crossover
When I was doing radical MGTD engines in the early 50's I closed
pipe with material and welded in a fill and smoothed, it did
power and amazing it also smoothed out the idle on a big camshaft.
engines had a single port for two combustion chambers. It so
amusing that when
I sold my MG special that had that manifold on it the guy thought
I trying to
pull something off on him cause the idle was pretty smooth for
a big cam. I
drilled a 1/2" hole in the balance pipe covers and the idle
came right back
rough as a cob and he was happier.
I was talking to Jimmy Coan just yesterday about this, and
he remembers I
did it on the TR-4 in the engine dyno and the mid range and idle
characteristics were so bad we had a hard time stopping the
shaking out of the cradle. From this even though the flow bench
said other, I
passed on the mod. With the S.U.s or Stromberg it is important
but of course
on Webers each inlet port has it's own carb so no contest there.
The cross over balance pipe contributes to the flow of the
mixture when you
have only two carbs for four cylinders.
Lets start with the mixture flow going to number one, then
the flow must
reverse itself to get to number three, this makes number three
leaner, but now the inertia of flow is going to three and the
next open valve
is number four so it gets a higher inertia of flow, then to number
two and the
reverse takes place and the flow is leaner as the inertia of
flow was going in
the opposite direction, but number one now benefits from the
flow to number
two and so it is slightly richer than number two. make sense?
It really works
that way and is the reason I always check the number two and
three plugs on a
full throttle clean shut off. Those cylinders are most prone
because of this.
This being true ( and it is) you would think that plugging
the balance pipe
would better all around, but it's not. Weird!! Your power may
differ. I did replace the balance tube with clear tubing
and you could see the mixture
pulsing back and forth. Interesting , but of little value.
Never Be beaten by Equipment
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