Problems with lightweight flywheels and underdrive pulley?

[scottzg]

The concern of the lightened pulley is that the change will alter the crankshaft's natural frequency. The engine is counterbalanced for certain problem frequencies, and the lighter pulley and flywheel alter where the frequencies are. So maybe cruising along at 21mph could give you catastrophic bottom end failure. Or it could induce mircofractures the bite you way down the road.

Or so Mr. Dinan says.

[Mr.Pessimist]

So if you're crusing down the road and your crank begins to hit natural freqency and "break apart", wouldnt you be able to feel that?

I believe that I know my car well enough that when something aint right I can either hear it or feel it. I find it hard to believe that IF this all is true, I wouldnt be able to catch it until its too late.

In addition, I have a lightened pulley and I havent felt or heard any problems with the engine. My gas mileage has gone down, but I truely account for this by switching to another brand of synthetic oil about the same time as installing the pulley. I just honestly dont believe that a lighter pulley would decrease gas mileage, if anything it would help by reduce load on the engine.

So, I'm switching back to Amsoil synthetic and I'll let you guys know of any change.

Oh, I almost forgot. I have read time and time again, not to go below a 14 lb. flywheel when using a lightened crank pulley. However, is that much different from stock? How heavy is our stock flywheel?

[Legacy777]

You're reducing the load on the engine......it better improve power, reduce gas consumption, or both....depending on how you drive.......

Your car obeys the laws of thermodynamics