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Old 02-12-2021, 05:04 PM   #21
Synchro909
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Default Re: Lightened Flywheel?

IMO, this all boils down to how you will use the car. If it is around town, a lighter flywheel is probably better, especially if you drive it like a modern car and it sounds like a lot of you do. All the talk of spooling up faster etc indicates to me that you want to drive it like a sports car. That is not what they were made for
I do a lot of long distance touring on open roads so I stick with a heavier flywheel in that car. In another, which I use for all sorts of things and is more often in traffic, I lightened the flywheel. Horse for courses! Idle is much better with a heavy one and once up to speed, it makes NO difference, in fact, I feel it smooths things out, even at 50mph. Down shifts are easier but up shifts take a little longer - so what!
Drive it like Henry intended, changing up early, drive steady and a heavy flywheel is better. Drive like a modern car and a lighter one suits better. IMO, It takes self discipline to drive the way they did in the day when you're tangling it with modern traffic.
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Old 02-12-2021, 07:36 PM   #22
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Default Re: Lightened Flywheel?

A lot of disatisfication with vibrating model A/B engines can be attributed to NOT balancing the flywheel assembly after lightening.
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Old 02-12-2021, 08:02 PM   #23
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Default Re: Lightened Flywheel?

Here is the math. So if you reduce the diameter by half and keep the mass the same you reduce the inertial to one-fourth. If you also remove weight by machining off the outside diameter you will reduce the inertia even more, to 1/16 if my calculations are correct. The weight of a lightened flywheel is taken off of the outermost radius so the effect is more than what you would expect by just comparing the weights.
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Old 02-12-2021, 08:29 PM   #24
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Default Re: Lightened Flywheel?

For the disk, the mass is proportional to the area. The area of the original disk is pi X R squared. If you reduce the diameter of the disk by machining it to half the diameter, the area is pi X (R/2) squared or 1/4 of the original. So the inertia of the machined disk is 1/4 x 1/4 or 1/16 of the original.
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A is for apple, green as the sky.
Step on the gas, for tomorrow I die.
Forget the brakes, they really don't work.
The clutch always sticks, and starts with a jerk.
My car grows red hair, and flies through the air.
Driving's a blast, a blast from the past.
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Old 02-13-2021, 05:26 AM   #25
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Default Re: Lightened Flywheel?

A senior project in mechanical engineering school for us was to design a flywheel for a Gyrobus. The challenge was that if the shape was the traditional thick rim style, the stresses were too high and it would fly apart. After computer iterations, it came out as a thin rim, tapering to a thick hub. From the link, you can see the real ones weren't much faster that a Model A, but a lot heavier.
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Old 02-13-2021, 07:54 PM   #26
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Default Re: Lightened Flywheel?

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Modified STOCK flywheels should be banned and made illegal.
If a stock flywheel blows up and takes your legs off, you can sue the manufacturer.
If a modified one blows up, you don't have a leg to stand on.
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Old 02-13-2021, 08:19 PM   #27
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Default Re: Lightened Flywheel?

Quote:
Originally Posted by pete View Post
modified stock flywheels should be banned and made illegal.
If a stock flywheel blows up and takes your legs off, you can sue the manufacturer.
if a modified one blows up, you don't have a leg to stand on.
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Old 02-13-2021, 09:22 PM   #28
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Default Re: Lightened Flywheel?

As I recall, 30 lbs off of mine.
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Old 02-13-2021, 11:22 PM   #29
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Default Re: Lightened Flywheel?

Not sure I can answer the OP’s question, but with my recent installation of a rebuilt engine, I also installed a machined-down flywheel and V8 clutch/pressure plate. The flywheel still feels very heavy to me, but obviously is lighter than a stock A flywheel. The V8 clutch is very smooth.

Jim
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Old 02-16-2021, 02:30 AM   #30
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Default Re: Lightened Flywheel?

Quote:
Originally Posted by Pete View Post
Modified STOCK flywheels should be banned and made illegal.
If a stock flywheel blows up and takes your legs off, you can sue the manufacturer.
If a modified one blows up, you don't have a leg to stand on.
Hey Pete,
Yeah, you convinced me ! I’m a believer in Murphys Law !
Think I’ll stick with STIPES aluminum flywheel !!
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Old 02-16-2021, 06:57 AM   #31
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Default Re: Lightened Flywheel?

The forces on a flywheel at 2000 revs are not going to be anywhere near 8000 revs.
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Old 02-16-2021, 07:37 AM   #32
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Default Re: Lightened Flywheel?

So at 8,000 rpm my Fordor with the present gearing and in high gear and overdrive would be going 220 mph. Guess I'll head for the salt flats.
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A is for apple, green as the sky.
Step on the gas, for tomorrow I die.
Forget the brakes, they really don't work.
The clutch always sticks, and starts with a jerk.
My car grows red hair, and flies through the air.
Driving's a blast, a blast from the past.
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Old 02-16-2021, 07:53 AM   #33
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Default Re: Lightened Flywheel?

this discussion is often brought up on the early 1 and 2 cylinder cars- where the weight of the flywheel is really meaningful.


with a 4 cylinder engine- not so much.
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Old 02-16-2021, 12:28 PM   #34
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Default Re: Lightened Flywheel?

To Pete's point, lightened stock flywheels are verboten in SCTA competition.

I have been looking at some of the "lightened" flywheels and noticed that some have material removed from a inside. While this will reduce the weight, it does not address the MOI calculation.

I have been working on some FEA analysis of this and the hub strength. Preliminary MOI shows that there can be as much as 35% reduction in MOI by removing weight off of the OD vs the ID. This in itself will reduce the amount of hub stress too.

Still a ton of work to do on this, computer time is limited, J
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Last edited by johnneilson; 02-16-2021 at 12:29 PM. Reason: correction
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