I'm building a 2.0 litre blacktop Zetec engine to fit into my Focus next year and I've been looking into fitting something other than a standard open diff into the gearbox to mate up to the new engine.

As the car is currently a 1.8 it has the IB5 gearbox for which I can fit a Ford Racing Puma viscous lsd into it - alternatively I've got an MTX-75 gearbox available to me in which I could fit a Quaife ATB diff as fitted to the Focus RS.

Unfortunately I've never driven a car with a trick diff in it so have no idea how crude/effective a viscous lsd is or whether it's worth paying a little bit extra (and finding a host of other parts to make the gearbox fit) for a Quaife jobbie.

Anyone any advice? Anyone driven with both a viscous diff and an ATB? I'm looking at running around 170-180bhp which doesn't sound like much but the car is going to be a track/sprint car so will spend a lot of time going round corners at full chat.

Cheers in advance