In our dyno testing we've found that larger carbs almost always (note the
"almost") make more peak power numbers than smaller ones provided they are
tuned to roughly the same fuel curve. In fact, I once made the best peak power
with a Chevy 305 and a 850 cfm carb on a Victor Jr.--a combo that no one said
would work. However, that's racing dynos--wide open against a load. In
practical driving, the throttle bores are too big to maintain airspeed against
a part-throttle load, and hence, it seems they don't pull on the booster enough
to suck fuel. Too much slow air, not enough gas = bad. Perhaps the dynamics of
land speed would be similar enough to dyno conditions that overcarbing could be
good provided that you can keep your engine speed high and in a very narrow
band even after shifts.
DF
>>> Dick J <lsr_man@yahoo.com> 6/20/01 4:54:55 PM >>>
Here's one I've wondered about for a long time.
I know that on street cars and drag cars,
over-carbureting knocks out your bottom end
punch. But, for LSR, why would over-carbureting
be a problem. Or what I really mean is: "Can
over-carbureting really exist in LSR?"
I remember using an old fashioned hand pump to
inflate a flat tire on my dad's truck. It got
real hot (loss of energy) and real hard to pump
up and down (more loss of energy) if you tried to
pump it too fast.
Isn't that exactly what a car engine is doing.
The piston is going down on "intake" and trying
to pull a vacuum a lot faster than atomospheric
pressure can fill the hole (otherwise there would
be no advantage to supercharging.) If the
atmosphere is trying to push into the vacuum
through four 1.25" throttle bores, isn't the
motor using a lot of it's own horsepower just to
try and create more of a vacuum than the
atmosphere can fully fill? Wouldn't it be a lot
easier to breath through four 1.50" bores, or
maybe eight 1.25" bores? I mean, no more air or
fuel mixture is going to enter the engine than
what the capacity of the cylinders dictates, but
it would get in there with less resistance.
If the "ideal" flow for a given motor is a 750
CFM, it just seems that it would still pull 750
CFM through TWO 500 CFM carburetors, but with a
lot less work than through a single 750 CFM rated
carburetor.
I know, you lose some charge velocity if the
intake area gets too big, but it still seems that
the HP loss through the breathing restriction at
wide open throttle would eat up a lot of
horsepower.
=====
Dick J
In East Texas
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