Assume we want to rev from 1000 to 2000 RPM in one second
Oooooh! Numbers! I was too lazy. Thanks!
Now, note that 1000 to 2000 in one second is too slow. That’d be
five seconds just to get wound out in 1st gear and we haven’t even
gotten to second yet. So, for an example, I’d presume a spin-up rate
about double that, 1000 to 2000 in a half second.
Assume the flywheel is 30 lbs (14 kg)
I think this flywheel is heavier than that. Somehow I recall 44
lbs as being the number, but I may be thinking of something else.
Assume the flywheel mass is distributed evenly as a disc.
It’s close, except the inner five inches or so is considerably
thinner and lighter, which means a higher percentage of the mass is
So cutting the flywheel weight in half will free up another ~9 ft-lbs
to the input shaft of the transmission.
There’s a good question: Is going to an aluminum flywheel really
cutting the weight in half? That’s probably about right, I think,
although it’s possible that it removes a bit more weight from the
outermost portion, presuming the steel face plate isn’t the full
diameter of the flywheel.
For a while, I was considering just sending my OEM steel flywheel out
to have half the mass machined off of it. It’d actually be fairly
easy to do. Rather than the back side being flat, I’d machine most
of it away leaving the plate less than 1/2" thick and leaving a
flange to hold the ring gear. I’d drill out the clutch plate
mounting holes and mount it with bolts with nuts instead of threaded
holes in the flywheel. I’d also consider scalloping the OD between
the clutch plate mounting holes, since all that outboard mass is good
for nothing. This was all before someone explained to me how you
make an aluminum flywheel with a steel facing. I suppose you could
actually do both, making an aluminum flywheel and making it a bunch
less bulky than the OEM steel flywheel. Could even drill holes in
it, leaving the steel face plate undrilled.
Bear in mind that there are
a lot of other rotating pieces in motion. The crankshaft alone weighs
about 70 lbs. As does the accessory drive full of cast iron pulleys.
True, but all of those items are considerably smaller diameter than
the flywheel, so their moments of inertia are less significant. The
biggie, really, is the pressure plate, but I don’t think there’s any
good way of reducing the moment of inertia there without going to
esoteric racing hardware.
I have gone so far on mine as to install a lightweight flywheel,
carbon fiber drive shaft, electric fan, simplified accessory drive,
aluminum water pump pulley, electric power steering and lightweight
wheels. All in an effort to pull rotating mass out of the system.
There is another factor at work, of course, and that is the EFI
system. As I understand it, it doesn’t respond well to snap accels.
It was never designed to; it was supposed to be used with an A/T.
So, you’re at idle, you stomp it, and the engine is at 5000 rpm while
the MAP sensor – at the end of ten feet of tubing – is still
thinking the engine is at full throttle at idle. The fuel/air ratio
may be all messed up. It’s this sort of thing that Bywater addresses
with his Super Enhanced ECU’s.
Still, it´s the journey not the destination, and as a mechanical
engineer I love discussions like this.
I’m glad we can keep you entertained!
Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !On 20 Oct 2015 at 10:22, Gary Evans wrote: