Wow what a difference that makes!! even though I was not used to the Z as I have not driven it for over a month and stalled it at the lights :wack: LOL the pulley really does make a real difference, one thing I notice is I dont have to put my foot so far down on the go pedal for the revs to increase :dance: But I will give it another go in the daylight tommorow as I have to wear the new tyres in, but soon I can drive it again like it's meant to be driven :dance: :dance:

I assume the underdrive pulley is not only lighter than the original but drives the alternator / fan at a lower speed as it's smaller so puts less load on the engine.

That would be why it can have a more dramatic effect than lightening the flywheel by the same amount.

Just a guess...!

 

the underdriving only accounts for about 10% of the power gain as it doesnt underdrive by a huge amount on our cars

Had this for a while now and fitted the other pulleys at the same time. Engine feels like it revs quicker. good bit of kit

the way people go on,saying a lightened flywheel is fantastic driven 3 or 4 zeds including my own which has an rps lightened flywheel it may reduce mass,but i wouldnt say its an unbelievable differance yes may be a bit more revy but unless you have a spare £400 i wouldnt bother IMO