Hi guys,
The idea of using the flywheel as a vibration damper is interesting, but
false. The firing of the four cylinder engine every 90 degrees gives
different harmonics at different RPM.
To truly overcome this problem, the real solution is to use a variable
harmonic damper such as is used on modern racing cars.
The point of a flywheel is threefold: One, it gives enough stored energy up
to maintain low RPM operation, Two, it gives the starter motor a small to
large gear ratio (mechanical advantage) to start the engine, and three, it
allows stored energy in the flywheel to be used to start the car from rest.
Modern cars use a damper that is generally tuned to a specific RPM/harmonic
range, and some devices such as the FluidDamper is able to damp the
harmonics at a wide range of operation.
Why damp harmonics?
Harmonic vibration is like a lot of men marching across a bridge in step.
The harmonics cause the bridge to fail.
In much the same way, harmonic vibration can destroy your crank and other
parts of the rotational mass.
Balancing helps, but you need a mass at both ends of the crank to do the
job.
With a low compression engine such as the XPAG or earlier units, the only
thing a lightened flywheel would add is rev-ability.
The main problem is piston velocity in feet per second through the bore at
high RPM.
I would be interested in hearing from anyone who actually races an XPAG or
cammer engine to explain what he does to his engine for high RPM usage.
Best,
Ray McCrary
"Speed is Life;
of course Luck and Altitude
are helpful, too."
----- Original Message -----
From: "Dwyer" <jasper@enternet.com.au>
To: <mg-mmm@autox.team.net>
Sent: Wednesday, April 25, 2001 9:15 PM
Subject: Re: Lighten Flywheel - was Clutch
> Lance
>
> You're quite right: the weight of the flywheel is there to smooth out the
> power pulses of the engine. The snag is that in some cases the dampening
has
> been a bit overdone, even for road use. This results in an engine that is
> slow to change its rpm, and especially if you have a crash box that makes
> gear-changing more difficult.
>
> The standard P-type engine feels to me quite ponderous in its response.
The
> flywheel and clutch assembly on this 847cc engine weighs quite a bit more
> than those of a 1250 TC. Cars in the 30s had only limited rubber
insulation
> between engine and chassis and the heavy flywheel was an effort to reduce
> perceived vibration. I think that the fuels available at the time also
gave
> less smooth running than we are accustomed to.
>
> Of course if you reduce the flywheel/clutch mass too much the engine will
be
> unpleasantly rough at low revs. However I don't think that there's much
> chance of reaching that stage with a P-type!
>
> Regards
>
> Dave Dwyer
> J2, TA, TC
> British Cars Web: http://www.team.net/sol
> MMM list subscription info: http://www.team.net/cgi-bin/majorcool
British Cars Web: http://www.team.net/sol
MMM list subscription info: http://www.team.net/cgi-bin/majorcool
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