Dual Mass Flywheel
The total mass of the dual mass flywheel is optimized from the factory to lessen and dampen natural engine harmonics. Buy adding and subtracting mass and altering stiffness values, engineers can modify and shift and tune bending modes in a measured and concerned axis. Peaks or bending mode shapes are identified buy measuring acceleration rates. At various frequencies each part has a contribution to total stiffness and mass and are all dependant of one another in a system. The total free wheeling mass of the flywheel in a non-coupled state has not changed in total stiffness or mass. But buy coupling up the transmission, the dynamic modal stiffness values of the system + flywheel and transmission change to a completely different state. This transition state is designed from the factory to add rotational mass and stiffness at a predefined slope to help dampen rotational shock loading, offer longer life, and add good sound NVH characteristics.
On a fixed tuning fork you will always get a predefined frequency in which it resonates. If you where to take mass out and keep the stiffness value the same, the frequency would always rise and hence shift the resonating frequency mode. Mass and stiffness values along with other variables, shift modes. If you have two modes that are in phase they are considered amplifiers, and if they are out of phase of each other they are considered dampers. Since the flywheel is balanced, engineers will optimize its mass property because it’s quite obvious that the rotational shear stiffness value is dam stiff between the crank and the flywheel…as you can imagine. Because Force is equal to mass times acceleration, the system should have the same signature through out the reciprocating components rotation cycle from 0 – 360 degree’s. Force will change dynamically and is dependant of all other things…that I’m sure you can imagine. Acceleration is dynamic but is mostly repeatable and should not change from the standard OEM modal alignment.
Adding a lightweight flywheel on the factory 2jz-gte engines is not such a great idea and significantly alters the mass on a relatively long crankshaft. If you purchased a lightweight flywheel and had an OEM or aftermarket crank balanced with the flywheel to with in a half of gram…consider your self “Golden”.
Will a couple of thou off the flywheel change the mode shape?? Maybe a very small increase in frequency…but I doubt that it will cause concern in the OEM modal alignment causing a failure or amplifying another mode.
Will the metal chips get inside the flywheel and change the slope of the engagement? That depends on what type of machining is being done and has been noted on the Mkiv.com doc lists.
If you are running a high horsepower supra with a stock factory engine you will reach a point were you are breaking stock dual mass flywheels…so save your old stock flywheels and have them reground. Then simply clamp the flywheel (with a lot of force) in a big vise and weld the two disc’s together making sure the welds are symmetric.
Drag racers don’t care about shock loading and good NVH characteristics…they just don’t like spinning rod journal bearings!
