belize1334
Well-known member
Been a while since I posted a geeky techy article...
I happen to have my hands on an ACT streetlite flywheel as well as a Fidanza aluminum flywheel so I thought I'd compare their respective MOI since the listed parameter is flywheel "weight" which is only vaguely relevant.
The experiment goes as follows. Connect the flywheel to three pieces of string and fasten them all together a fair distance above the surface. Twist the strings together several times. Hang the flywheel from the strings and watch it start to spin. The time it take to unwind and then wind up again is proportional to the square_root of the MOI divided by the mass. That means the MOI is proportional to the mass times the square of the time for one "oscillation". So by comparing oscillation times of different objects you compare their MOI.
Results are based on published weight of flywheels and estimated weight of a typical pressure plate found from various threads. If you object please comment.
Fidanza: 8lbs, 68s, MOI ~ 36992
ACT : 12lbs, 67s, MOI ~ 53868 or 46% greater than Fidanza
pressure plate: 10.5lbs, 60s, MOI ~ 37800 or 2% greater than Fidanza
ACT FW + pp ~ 23% greater MOI than Fidanza + pp
The moral... You can think of the Fidanza FW as equivalent to another pressure plate. The ACT unit is like 1.4 pressure plates. The disk is an unknown factor which doesn't affect free-reving but will contribute to accelleration load in a marginal way. And, importantly, both flywheels have almost identical mass distributions so the weight is a very good proxy for MOI when comparing them. Unfortunately I don't have a stock cast-iron flywheel so there's no way to say how either compares to that. These are both much lighter but the distribution of mass relative to OEM is unclear so we can only speculate. If someone has both an OEM flywheel and one of the two listed then they could repeat the experiment and complete the set.
I happen to have my hands on an ACT streetlite flywheel as well as a Fidanza aluminum flywheel so I thought I'd compare their respective MOI since the listed parameter is flywheel "weight" which is only vaguely relevant.
The experiment goes as follows. Connect the flywheel to three pieces of string and fasten them all together a fair distance above the surface. Twist the strings together several times. Hang the flywheel from the strings and watch it start to spin. The time it take to unwind and then wind up again is proportional to the square_root of the MOI divided by the mass. That means the MOI is proportional to the mass times the square of the time for one "oscillation". So by comparing oscillation times of different objects you compare their MOI.
Results are based on published weight of flywheels and estimated weight of a typical pressure plate found from various threads. If you object please comment.
Fidanza: 8lbs, 68s, MOI ~ 36992
ACT : 12lbs, 67s, MOI ~ 53868 or 46% greater than Fidanza
pressure plate: 10.5lbs, 60s, MOI ~ 37800 or 2% greater than Fidanza
ACT FW + pp ~ 23% greater MOI than Fidanza + pp
The moral... You can think of the Fidanza FW as equivalent to another pressure plate. The ACT unit is like 1.4 pressure plates. The disk is an unknown factor which doesn't affect free-reving but will contribute to accelleration load in a marginal way. And, importantly, both flywheels have almost identical mass distributions so the weight is a very good proxy for MOI when comparing them. Unfortunately I don't have a stock cast-iron flywheel so there's no way to say how either compares to that. These are both much lighter but the distribution of mass relative to OEM is unclear so we can only speculate. If someone has both an OEM flywheel and one of the two listed then they could repeat the experiment and complete the set.
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