Engine Flywheel Question

GoldenEagle91 · Jan 26, 2015

Hello everyone,

I recently have begun reading Herb Adams's Chassis Engineering book which I highly recommend to anyone who wants to learn quality information regarding chassis design and engineering. At any rate, he has an example in his book towards the end where he is talking about how a reduction in rotating inertia in the driveline accounts for quite considerable gains in acceleration and speed. I have been rebuilding an engine for a good while now and I had the rotating assembly balanced. This included the crank, rods, pistons, harmonic dampener, and flywheel.

The question that I have now is this: If I were to pick up a lighter weight flywheel now before installing the engine, would it throw of all the balancing or should it not be an issue?

Part of me thinks it would be okay considering people throw lightweight flywheels on engines all of the time and I don't imagine they have problems but the other part of me thinks that by switching to a lightweight flywheel when the rotating assembly was balanced with a heavier steel flywheel that it might throw things off.

Stay Shady · Jan 27, 2015

As long as the flywheel is the correct imbalance, it will work. From what i've been explained, lighter weight are for road courses where you'll be accelerating and decelerating constantly. Less rotating mass to stop and then start again.

2000xp8 · Jan 27, 2015

For a car mostly for the track, use whatever you like.
If this is mostly a street car that will see stop signs and lights, stick with steel or iron, they are just easier to drive. Not to mention much cheaper.

7991LXnSHO · Jan 27, 2015

To clarify, it is not the total weight of the flywheel that keeps the motor from vibrating. It is the imbalance, like adding weights to your rims, that offsets the weights in the motor. 54 oz and 28 oz balances are popular 302 or 5.0 L weights. Some race motors are balanced internally for zero balance flywheels and harmonic balances. Mix this spec up, and the motor will shake badly as RPMs increase.

The total weight of the flywheel is instead a matter of rotational inertia, and that can change drive ability and acceleration characteristics.

GoldenEagle91 · Jan 27, 2015

Stay Shady said:
As long as the flywheel is the correct imbalance, it will work. From what i've been explained, lighter weight are for road courses where you'll be accelerating and decelerating constantly. Less rotating mass to stop and then start again.

My exact understanding.

2000xp8 said:
For a car mostly for the track, use whatever you like.
If this is mostly a street car that will see stop signs and lights, stick with steel or iron, they are just easier to drive. Not to mention much cheaper.

I follow what you are saying. So if I am interested in reducing rotating mass in the driveline then your suggestion would be to stick to changing the driveshaft, correct? The benefit to the reduced weight in the flywheel is a faster revving engine but at the same time it could/would make it more difficult to drive.

2000xp8 · Jan 27, 2015

GoldenEagle91 said:
My exact understanding.

I follow what you are saying. So if I am interested in reducing rotating mass in the driveline then your suggestion would be to stick to changing the driveshaft, correct? The benefit to the reduced weight in the flywheel is a faster revving engine but at the same time it could/would make it more difficult to drive.

Pretty much. Most people I know that had street cars and when from iron or steel to aluminum weren't real happy with the result.
Now the driveshaft i'm all for. Totally smooths out drivetrain. It would be high on my list of things to do first if I was starting over with a stock car. I'd put it before quite a few other things.

GoldenEagle91 · Jan 27, 2015

2000xp8 said:
Pretty much.
Now the driveshaft i'm all for. Totally smooths out drivetrain. It would be high on my list of things to do first if I was starting over with a stock car. I'd put it before quite a few other things.

I will take your advice on the driveshaft. Any suggestion of brand? Is the FRPP one just fine or is there actually a benefit from going to the more expensive one on AM( http://www.americanmuscle.com/aluminum-driveshaft-7995v8.html ). They say there that they would shed up to 29 lbs of rotating mass from the driveline. Does anyone know the weight savings from the FRPP one?

2000xp8 · Jan 27, 2015

I like the ford racing one, not sure about any other brands. When it comes to things that rotate, like flywheel, driveshaft, balancer and gears I've always stuck to ford racing.

GoldenEagle91 · Jan 27, 2015

2000xp8 said:
I like the ford racing one, not sure about any other brands. When it comes to things that rotate, like flywheel, driveshaft, balancer and gears I've always stuck to ford racing.

Sounds like a plan my friend

Engine Flywheel Question

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