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-   -   Light weight flywheel - good idea? (http://www.clubcobra.com/forums/small-block-talk/67769-light-weight-flywheel-good-idea.html)

Jeff Frigo 04-02-2006 03:56 PM
Quote:
Originally Posted by Cobra 29
I have a FMS 351W crate motor... My ERA Cobra...
Sacrilege:eek::CRY::eek:

PDUB 04-03-2006 12:15 AM
Quote:
Originally Posted by DavidNJ
I actually used kilograms and coverted back...never could keep the English units straight. Matcad does the unit conversions for you though, In this case the constant, g, is the same on both sides so the ratio holds.

However, you are correct, I forgot to convert diameter to radius, so I was off by a factor of 4. This would make the energy equivalent to around 2mph. I knew the number should have been around 4-6 lb*ft²...so I must have been asleep at the wheel here. There is probably another 1-1.5 lb*ft² from the crank, rods, pistons, pins, rings, and bearings.

David,

Yes, kilograms work, as this is the SI unit of mass. Yet, the masses of the two are an order of magnitude apart, so you would expect a significant variation in their velocities in order for them to maintain the same energy level. Yes, about 2 mph works:

Set the two equations equal to each other, and solve for the velocity of the car.

KE(flywheel) = KE (car)
457.78ft-lb = 0.5(2800/32.2)(v)²
(457.78)/[0.5(2800/32.2)] = v²
(457.78/43.478) = v²
(10.529) = v²
v = (10.529)^(1/2) = 3.24 ft/s = 2.21 mph


You lost me on the units in your reply above (lb*ft²)... if this is energy/torque, then I am thinking that there should not be an exponant, i.e. no squared for the ft units... is that correct?

I agree that the crank contributes, though it would be a bear to do anything but aproxiamte it:eek:! Don't forget the balancer, as these are typically about 8-inches in diameter and weigh in the 10-14 lb range, with most of the mass out at the perimeter of the disk.

By the way, how did you get the superscript on the exponant? (I cut and pasted, except for the 1/2 power (i.e. squareroot) at the end ;)

DavidNJ 04-03-2006 03:33 PM
Mathcad does the unit conversion. So if you get the same answer entering '45 lb', '20.412 kg', or '1.399 slug' . Using a MKS check provides a warning if the English units are wrong.

I use ATI dampers, aluminum shell with a steel hub. 6.325" OD with about 6# weight. I believe the other brands are similar in size, weight, and inertia.

Alt+0178 is a superscript ², Alt+0176 is a °.


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