That's pretty interesting. I might make note that the higher revs the
higher the air velocity the higher the velocity the lower the pressure,
therefore the flow of fuel will be HIGHER even though the needle has not
risen any higher in its taper. Funny stuff huh!!!.
----- Original Message -----
From: "Greg Solow" <gregmogdoc@surfnetusa.com>
To: "Friends of Triumph" <fot@autox.team.net>
Sent: Tuesday, October 14, 2003 8:56 PM
Subject: velocity stacks and stand-off
> While we were dynoing this 3/4 race engine (280 degree duration cam)
> installing the velocity stacks in every case made the fuel "stand-off"
> disappear. Without the velocity stacks there was a cloud of fuel in front
of
> the carb inlets that you could feel the wetness on your hand up to over 1
ft
> away. The fuel seemed to be in constant motion into and out of the carb
> throat. the fuel did not seem to "blow away" into the dyno room. When the
> velocity stacks were installed, the cloud was no longer there, and the
engine
> made slightly more power from the point where it came on the cam, ie.
about
> 3200 rpm up to around 4500 rpm. Above that rpm the power was always less
with
> the stacks than without them. d
> As I mentioned before, we did not have any "stub stacks" as
recommended by
> David Vizard as being a benifit on Minis and MG engines. So they are a
> questionmark as far as this engine is concerned. It is interesting and
> puzzliing when emperical results do not agree with what should the
theoretical
> results. Everthing I have ever read says that the stacks should make
things
> better everywhere, not worse. The square corner of the carb inlet should
act
> to in effect reduce the size of the inlet and reduce the air flow. Maybe
the
> power level of this engine does not require any more air and so that is
why it
> did not help.
> On Weber carburated engine, every time we have gone up in venturi
size,
> the power has gone up. But again this was on a full race engine making
well
> over 170 hp on this same dyno.
> By the way even on this engine, with either set of carbs, the air
valves
> were up all the way they could go by 4500 rpm. So from this point on the
> actual taper of the mixture needle is no longer having any effect on the
fuel
> metering. as only the exact point of the needle where it enters the jet is
> controlling the mixture and that is no longer changing as the revs change.
Of
> course the size of the needle at this point is important and is controling
the
> amount of fuel flow into the engine.
> Regards, Greg
Solow
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