Larry Colen wrote:
> While the engine is apart, I'm thinking of doing something
> about lightening the flywheel. I see that Moss wants $480 for
> an alloy flywheel. What does it normally cost to get a machine
> shop to lighten a stock flywheel? Are there other good sources
> for such?
Flywheel phsyics is a very interesting subject... the first thing you need
to know is that the Moss aluminum flywheel is overpriced by $150. You
should be able to obtain the exact same flywheel from a Fidanza distributor
located in Ohio... find Fidanza's website and look up who it is (his prices
are typically $325ish for MGs and TRs). I can not recall the name. Fidanza
flyweels are unmatched on the current market in terms of quality. They have
a very high quality friction face, which is replacable should you ever wear
it down.
Lightening your own flywheel will cost between $100-$250 depending on how
much material you take off, and how comfortable the machine shop is making
the modifications to your flywheel.
> Also, what are the downsides to a lightened flywheel? Harder
> to idle? Likewise, what are the quantifiable differences. If my
> 130 hp MGB will turn a 2:20 lap with a stock flywheel, what
> should I expect to see with a lightened one?
Your lap times will be dependant on your gear ratios with a lightened
flywheel. What you should see is better transient response from your car,
which means more time gained. The less time your engine has to spend
accelerating the mass of the engine internals (and driveline in general),
the better for your lap times.
The downside of lightening a stock flywheel is that you could potentially
neuter yourself or at least have to adapt your car to drive with hand
controls once you wake up and realize you do not have feet. Lightened TR
flywheels HAVE exploded and any serious Triumph racer now uses a 1/4" thick
steel scatter shield over their transmission tunnel. I expect the same goes
for any serious MG racer, but I suspect that they are already using
flywheels machined from either a solid piece of steel or alu (but that just
was not a cost effective option for a long time).
Aluminum flywheels are safer in this respect, but the mass is typically more
evenly distributed throughout the radius of the flywheel. With a NEW
machined steel flywheel, you can concentrate much more of the mass (since
steel is obviously more dense) towards the center of the flywheel. If you
try to do the same while lightening your stock flywheel you run the risk of
machining down into material that is not quite as hard or does not have the
same grain consistency as the other portions of the flywheel. This is when
it becomes dangerous...
Fidanza flywheels are made from tempered aluminum, it is good stuff. If you
use quality flywheel fasteners and if your dowels are a snug fit, you should
not experience any problems with bolt hole elongation on the aluminum
flywheels. The choices of aluminum that Fidanza specs match or exceed some
of the strength qualities of carbon steels.
Back to the talk about gear ratios. What follows is a VERY general and
conservative concept of what you will experience. If you remove 10lbs from
the flywheel, depending on your gear ratio in 1st gear, your car will behave
as if it has been lightened by 100lbs. Second gear the situation is not
quite as optimal, your car would behave as if it had maybe 60lbs removed.
The advantage is decreased with each successive change of gear. Or rather,
the narrower the usable rev range in a particular gear, the narrower the
opportunity is to gain an advantage out of the light flywheel.
Not to scare anyone with a lightened stock flywheel, most times machine
shops only remove a few pounds. It is the racing fanatics that always want
lighter and lighter flywheels that run into trouble when cutting down the
stock flywheels.
Kai (I value my legs)
/// or try http://www.team.net/cgi-bin/majorcool
/// Archives at http://www.team.net/archive
|