Hi Bill,
It is not so much a horsepower issue as it is a torque and momentum issue.
First, you are correct, it takes more power/torque to move a heavier
object.......it also takes less torque or resistance to slow a lightened
object.
The lighter flywheel compensates somewhat for the Healey's long stroke/small
bore (a function of UK taxation policy at the time) which, while providing a
very torquey engine, also makes it a lower revving, less responsive or "spin
easy" than a small stroke/big bore Italian engine or even the TR6 engine.
Horsepower is simply a function of power(torque)x speed (revolutions). As
such, a lighter flywheel will not affect horsepower. However, you are
correct in that the engine will reach it's powerband faster with the lighter
flywheel because it meets less resistance to change with a lighter
flywheel....an admirable trait for those who like spirited driving on
winding roads where one is constantly changing gears to keep in the power
range.
I personally like the lightened flywheel but as in most things, there are
downsides which you need to consider.
While an engine with a lightened flywheel will "spin up" to its powerband
much quicker, it will also loose momentum meaning that the engine will react
much quicker to sudden demands on Power such as starting on a hill. The
engine simply does not have the same critical mass as it used to. "Popping
the clutch" will more likely stall a car with a lightened flywheel than one
without...."it takes less resistance or power to slow a light object than a
heavy one".
If your car is a highway cruiser using the 3.54 gears, then I would stay
with the heavier wheel...it will be more comfortable.
If you like spirited driving on winding roads or like hillclimbs (my
favourite in Vancouver) and your using 3.9 or 4.11 gears, then go for the
lightened wheel. It also sounds nice when you pull up to a light and blip
the accelerator a few times.....
Good Luck
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