Aluminum or steel flywheel

[greg schroeder]

In my opinion and theory the aluminum is nice for 1st and 2nd gear as it carries less inertia on hard acceleration. In that it will adjust slightly better to road inconsistencies keeping better traction. Also I suspect the idea that the aluminum is a bit easier on the transmission because it has less inertia on shifts. Also there might be some value to forgive bad shifts a little quicker rather than having the mass of a really heavy flywheel carry the crunch and grind longer. The clutch will last longer with a lighter flywheel particularly if you’re in marginal HP values to the clutch ability.

Something heavier is an inertia push when you shift quickly to the next gear. If you have the traction to hook a 2nd, 3rd or 4th gear shift the heavy will give you a bit of go for an instant before it corrects to the next gear. The problem is you'll be hitting that gear and spin most of the time if you're on general road tires. The condition is exaggerated with a heavier flywheel, not fun. In that case the aluminum being lighter will hook the next gear faster as the RPM will correct lower to the next gear with less inertia.

I went from a heavy steel flywheel and replaced it with light weight aluminum. It’s more fun. There are no issues with street drivability.

[Chilibit]

Most of these comments have to do with the acceleration phase. I believe that less motor inertia will affect the downshift behavior and deceleration in general. I seem to have a natural rhythm on shifting which is not very aggressive. The decay time on the rpm's is important to my rhythm. I am not arguing that it is better, just that some setups suit me better. More of a satisfaction thing than a performance thing. A smooth oneness with the car is more important to me than the last ounce of performance.

[DanEC]

Great input thanks. A 30 lb steel flywheel might be a great compromise to suggest to the builder.

Keith Craft is putting together the motor and I am planning to have him get the clutch and flywheel and balance with the motor. He's use to people asking for aluminum flywheels, but then he builds some mega-HP motors for a lot of them.

Mine will have a 4.25 inch stroke, somewhere between 9 - 9.5 compression and he was thinking a 222 to 232 duration cam when we talked. I'm using a 3.31 rear and WR toploader. This is a street replica build and not a sunday race car so I'm interested in a smooth off-idle, first gear starts and reasonable driveability.

I know, I know - no overdrive 5 speed. I'm old school. I wouldn't know what to do with if the engine wasn't buzzying along on the highway somewhere around the crest of the torque curve. Believe me - this is going to be worlds better than my 427 Vette with 4.11 gears.

Dan

[Bobcat]

Generalization .... heavy car , heavy flywheel , light car , lighter flywheel . Some of my squirt racer friends had a program that told them what flywheel weight to run . But , a fairly heavy flywheel helped off the line as the engine didn`t bog and helped keep the rpm up when shifting . Again , it required experimenting at the track . On the other hand , when I ran dirt track , the lighter you got the flywheel , the better ( for me ) . The car accelerated faster out of the turn and decelerated quicker when letting off the gas ( One year , I machined the counterweights off the crank ... boy , did it rev quick and decelerate fast .... also destroyed bearings fast ! ) . Flywheel weight , IMO , is a personal choice .... I happen to like a light flywheel , but if you have a really long cam , a heavier flywheel can help the idle and starting from a stop .

Bob