Bob, I installed a Jim Donato aluminum flywheel on my TR3A daily driver last
year. This engine is otherwise stock except for a geared starter, very
tired stock camshaft and 87mm pistons & liners (also somewhat tired). I
switched to a 4-synchro transmission (with A-type) and a 4A style clutch at
the same time.
> I seen numerous advertisements for lightweight flywheels for our
> Triumphs, as
> well as many newer cars. What is the benefit the lightweight
> flywheel? Does
> it increase horsepower or torque?
It does not increase horsepower or torque, as measured by a dynamometer. In
fact, my "seat of the pants" opinion is that it actually decreases low rpm
torque somewhat, by letting individual cylinder firings become vibration
rather than power.
It does, however, make the car accelerate faster by, in effect, making the
whole car weigh less. In order to bring the car up to speed, the flywheel
has to be accelerated 5 times over ... once rotationally for each gear, plus
once as part of the weight of the car. The difference is not huge, but IMO
is definitely noticeable. The whole car feels more nimble.
Another advantage is that there is less of a shock transmitted to the
driveline (and car) if you (dis-)engage OD with the clutch engaged. Seems
like that has to translate to longer OD life, but they live so long anyway I
doubt I'll ever notice the difference.
But there are several downsides. The most noticeable is that the car is
harder to launch from a stop : it's easier to kill the engine, especially if
you're going uphill. Nothing you can't learn to deal with, but it took me
some time. Haven't killed it in a few weeks now, but having said that I'll
probably kill it tonight on the way home. (SoCA freeway entrance ramps are
a pain in a manual trans car.)
I suspect I'll also get shorter clutch wear, since most of the wear happens
when launching and I have to hold the revs higher when letting out the
clutch. Of course, part of my perception is the taller first gear ratio of
the 4-synchro box. I think most of the difference is due to the flywheel,
but I don't know that.
Another downside is that these things are harder to keep on the crankshaft.
Best practice appears to be to add another pin between the flywheel and
crank (which means the crank has to be drilled, my flywheel came already
drilled); and to use ARP high-tensile bolts to hold the flywheel on. Even
so, failures are more common than with the cast iron flywheel. I haven't
done either of these things (since I didn't want to pull the engine at the
time), but I will when the engine comes out next year.
The last downside is a little more subjective ... between the aluminum
flywheel and geared starter, it just doesn't seem like a TRactor motor
anymore.
YMMV
Randall
59 TR3A TS39781LO daily driver (back on the road, WooHoo!)
71 Stag LE1473L daily driver wannabe (waiting for OD transplant)
63 Sports 6 HB7826LCV rustoration project
57 TR3 TS21731L rusting quietly
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