Re: fan clutches, any difference btwn OEM & partstore>
No, there is no problem with the Z.
The aftermarket(non-OEM) fan clutches are more viscous and cause the fan to spin faster(the clutch offers less slip). This sucks more power that would otherwise get to the rear wheels.
This has been dyno proven, and can definitely be felt when driving the car.
As for the Jeep, a "flex fan" would seem to be the extreme case of viscous coupling, as in there is none. It is bolted right to the pump and spins at engine rpm. This would use the most power possible from the engine.
My fan clutch failled locked on my Z and it sucked a LOT of power, especially over 2500 rpm. The faster you wound the engine, the more resistance you could feel to acceleration.
Not my imagaination, fact.