Flywheel - to lighten...or not ?

[aussieTR]

I am undecided as to lighten the flywheel during the rebuild of my 4 cylinder TRactor engine.The car will be used mainly on the road. I've had differing opinions from the sages here in Oz. Some say leave it standard (heavy) while others say take as much off as possible.
I want a responsive drive, but don't want the car to bog down with too drastic a weight reduction.
My 3A has a lightened flywheel and along with a 4.1 diff and engine mods, it gets off the mark with no problems.
Anyone have any suggestions of a suitable compromise?
By the way, the TR4 has a 3.45:1 diff.

 

[Alan_Myers]

Hi,

3.45:1 is a non-standard gearing for a TR4, at least here in the U.S and in England. I think the car will be a bit slow off the mark with that ratio, but it should cruise nicely at 85 mph! 3.7:1 is most common and 4.1:1 is a fairly common option. Some racers use 4.3:1 or 4.5:1, if they like to hear the engine scream.

The TRactor revs up pretty well, but I'm installing an aluminum flywheel in my TR4 anyway. In researching this, I found several options and a lot of opinions. There is a middle ground with moderate lightening of the stock flywheel, if you are concerned about getting it too light. You can always take off more later, if you wish. But, I'm thinking the axle ratio may be the biggest limiting factor of your car.

The stock flywheel is quite heavy. If extensive flywheel lightening is done some other dampening, such as a harmonic balancer at the front, and an overall carefully balanced engine would be a good idea.

Just my 2 cents worth.

Cheers!

Alan

 

[Dave Russell]

Correct flywheel weight it largely a matter of perceived driveability & quick throttle response.

Light flywheel advantages; the engine will rev quicker under light load conditions & in the lower gears. There is progressively less advantage as you shift to higher gears. The engine will also drop rpm quicker when the throttle is closed & or when load is removed. These are advantages in a race situation where quick throttle response & gear shifting are important.

Disadvantages; It will take more throttle & clutch slipping to get the car rolling. The idle rpm may have to be set higher. Low rpm throttle response will be lessened.

A conservative approach would be to remove 5 to 10 pounds close to the outer periphery of the flywheel. Material removed near the center will give less benefit & may dangerously weaken the flywheel. Any flywhell which has had material removed should be re-balanced.

It all depends on how much you wish to slip the clutch & rev the engine to get rolling. A 3.545 axle ratio already requires a bit more clutch slipping to get rolling over what a 4.1 axle ratio would. An interesting example would be a Formula 1 car with practically no flywheel, which requires 9,000 rpm & either a lot of clutch slipping or wheel spin to get rolling after a pit stop. Even then the driver frequently kills the engine on a restart.

Think of the flywheel as a stored energy device which helps get things moving. The heavier it is, the easier to get the car moving. Secondarily, it provides a smoother slower idle.
D