On Wed, 19 Feb 2003, Simms, Bruce CIC wrote:
> An LBC shop owner advised me not to lighten the flywheel on a street driven
> TR6. He said you might gain high end horsepower, but would lose torque.
> Comments?
Please hold on for a minute - I need to vent.
AAAARRRRGGGGHHHHHH!
There, I feel better.
You do not _create_ HP by lightening the flywheel. You might free up some
ponies, but you do not create power this way.
What you are doing is decreasing the interial _load_. This gives you
better acceleration and that is only felt in the lower gears. So, if your
goal is to accelerate faster, lightening the flywheel is a way to get
there.
You gain nothing at the high end other than the lower inertial load and
its effect with respect to harmonic resonance. But because of the inertial
mass of the crank assembly, a few pounds at high RPM is in the "noise"
with respect to performance enhancement.
Using Shane's *and Mike M's) reference to Mr. Kastner, the less weight on
the flywheel when things start to resonate, the less total flex in the
crank.
So - here's two conclusions:
1. lessening the mass of the flywheel has two measurable benefits, better
acceleration (ergo, the motor spools up faster) and less tortional load on
the crank during periods of high amplitude resonance.
2. assuming high RPM operation, there's less chance of crank failure with
the lower mass.
If you could do it - going to a real race clutch (bear with me please)
such as a 10000 RPM brand unit which weighs in at about 11 pounds total,
you should get a lot less crank flex than you would with a lightened
flywheel and a stock-ish clutch pressure plate... however this would be
totally undrivable on the street (because of the solid-center clutch disk
and the friction material (which has a very high CofF), all clutch
modulation on a race setup is done with tire slip which will def. get the
attention of the authorites.
But to the subject at hand, lightening the flywheel is a noble goal.
Lightening it properly (so as not to weaken it) is CRUCIAL, and lightening
it too much is probably a bad thing. Flywheels above 15 pounds are
probably okay, going much lighter on a stock TR6 flywheel is excessive.
Last - in any case, proper flywheel attachment bolts are CRUCIAL and
proper fastening is imperitive. Torque to spec and use (high
strength) loctite. If you want fasteners that are better than the stock
units, there are bolts available from ARP which are highly recommended,
but any bolt that is _hard_ is what you want to get. Not grade 8! Use
toolsteel bolts (this is according to Mr. K). I like the ARP bolts because
they are high grade, they have 12 point heads and the body to head
interface is radiused (requires a special washer) so the head will not
shear off. At about $15 for the bolts and the washers, this is cheap
insurance. HOWEVER - if you do wind up overrevving (for whatever reason),
it is prudent to pull the tranny and clutch and make sure the flywheel
attachment bolts are okay. As they say, to finish first, first you gotta
finish. I've seen plenty of Triumphs getting pushed into the trailer at
the end of the day (because the driver "got the red mist" and over-revved
the motor and the crank bolts sheared). Don't let this happen to you!
> Regards, Bruce Simms CF1941UO
Ta ta,
rml
CF14111U
CR1871OU
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