I would pay ten bucks to see a back to back test on a jet from a full on flywheel to a flex with no other changes. I'm not convinced that it would make that much difference being an you ate already spinning 40+ pounds of crap in the pump.
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That's one of the reasons I don't like them for a recreational deal. That gyro action (IMHO) weakens the center and causes cracks.
The SFI rating on them is null and void without a torque converter bolted to them.
The torque converter bolts to the outer perimeter and there is a centering button going to the crank. No wobble.
Again, I would use an aluminum flywheel minimum, but I'm retarded.
GT
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Hi GT, strange we actually agree on something without needing a ten page "debate" .
But don't forget the TQ converter is also supported by the input shaft of the trans. I wouldn't want to be within 100 yards of one running with no trans to support it. I bet it would flex that plate like a wet noodle.
I ran down to George at McLeod and ordered a 60# flywheel. Fortunately George talked me out of the 100# flywheel.
What I noticed, the engine revved A LOT slower, both free revving the engine and while accelerating the car. It also limited the peak RPM that the engine would rev. I couldn't believe it, all the work I had done to make it rev fast was gone!
Where you thinking it "limited the peak RPM that the engine would rev" because the car went through the traps at a lower RPM ?
With my own boat (V-drive). Running the flywheel it idled nice/smooth/quiet. Changed to a flexplate, idle was rougher and it caused a rattle from the V-drive. Flywheel was easier on parts because it didn't try to rattle the drive.
BTW, the engine turned the exact same max RPM with either one. IMO you should see no noticeable difference in max RPM unless your so far past your HP peek that your HP curve is falling like a rock off a cliff. Car would have had a slower trap speed and hence a lower RPM through the traps because it wasn't able to accelerate the added rotational mass as quickly, but eventually it would reach the same speed/RPM.
Flexplates or even flywheels have way less rotational mass using them in a boat than they do when used in a car. In a car the flexplate would have a big heavy TQ converter (full of fluid) bolted to it, and the flywheel would have a big heavy pressure plate bolted to it. Using either one without its bolt on parts results in way less rotational mass than in a car. But you also have to add any part of the drive system that rotates with the engine when the drive/trans is in gear. That goes all the way back to the tires in a car.
Lower rotational mass will allow the engine to gain RPM faster. But your already way lower than either would be in a car. And with a jet, where it can flash to max RPM at any time regardless of boat speed the only difference would be is the time it takes the engine to rev from idle to max RPM. A split second. Its not like the engine gains RPM slowly as it accelerates the boat, like it would in a car. Rotational mass determines how quick the engine can gain RPM, not how quick a jet boat can gain speed.
Only comparable way to compare the benefits or reducing flywheel/flexplate weight/mass between a jet boat and a car would be to time how quick an automatic trans drag car can gain RPM on the line from idle to stall RPM. At WOT the jet boat goes from idle to "stall RPM" and just stays there. Do you think changing flexplate weight would change stall RPM with an automatic trans ? The only benefit would be a very slightly reduced idle to stall RPM time. And at that time, the pump isn't properly loaded, so I doubt there would be any measurable difference in boat performance.
I vote for flywheel. Get the smoother idle and reduced abuse on the U-joints and pump shaft splines.
