My work with velocity stacks was always with FULL RACE engines. The purpose
of the stack use was to help contain the fuel standoff which appears at the
bottom of the rev scale (around 4000 revs) where the long overlap of the
camshaft tends to reject the air/fuel charge. But we were fortunate to make
very good gains in the entire rev range.My back to back tests with the GT-6
engine showed a improvement of 6-8 horsepower at 8000 rpm. In these tests, I
held the velocity stack up to the carburetors with my hands as the engine
was a full throttle and top revs, then removed the velocity stack and
watched the torque arm fall, pushed the stacks back into position and
watched the torque go back up and stabilize. We were all pretty brave
standing right next to the engine at full power, but trusted the engine
builder (me). Again this is with full race engines and big camshafts. I
think Gregs tests were great and give added information to all that there
are variables in this world of engine development and also points out the
wonderful information available from dyno testing..
So Joe, adding the air filter reduces the amount of air and therefore
indicates to me that there is either insufficient fuel supply (too small a
needle and seat) or a lean mixture at that higher rev point (needle shape).
----- Original Message -----
From: <N197TR4@cs.com>
To: <jaboruch@adelphia.net>; <fot@autox.team.net>
Sent: Tuesday, October 14, 2003 4:48 AM
Subject: Re: dyno test of TR-4
> Kas recounts some dyno work on a TR250 engine and making bigger HP by just
> changing velocity stacks.
>
> I am getting more anxious to check the efficiency of the ones my son Sean
> made out aluminum billet. Unlikely, but I think it would be a hoot if they
turned
> out to be heads above the alternatives.
>
> > I had a similar experience a few years ago with HS6 carbs. I could
> > not get any power over 6000 rpm on the track. I just could not get
> > them to flow enough fuel. I put air cleaners on to add some
> > restriction and gained 300 rpm on the straights. I did not, however,
> > go so far as to add the weber style spacers. Joe(B)
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