how good are 4 spider super diffs, this is fitted in a box I got from a mate who got it done at Dunhams. (Shimmo built).
question also, what are they like under racing conditions, drag or be it circuit.

Cheers

traction wise the same, just a lot stronger than 2 spider gear diffs

I ran/have one in my gear box. As steve said, no advantage in traction, but should make the box stronger. Combine with a heavy duty side plate and should hold the diff together longer. But if the engine is stock or close and your not flogging it, a super diff may not be needed.

I had the spidergears seize on their shafts due to burnouts,apparently with the extra cross shaft you loose some of the oiling holes i had dangerous redo the box and i coated everything inside withthe same coating you see on pistion skirts the diff copped it on the shafts,spider gears,the gear thing the fulcrum plates sit in and fulcrum plates.I've an easy 75 k on it now and no sign of nothing bad.The Grouch and Bluey both had issuses with the fulcrum plates and axle spades due to lack of oil(Both cars are low and are hiway haulers)The Grouch got coating on the spades and fulcrum plates,Bluey had modifcations to the diff by dangerous and coated fulcrum plates afaik no probs and matty is a burnout slut!Dave or matty can tell u about the mods,but i think that the coating is a good thing.I think Dave said that wheelspin the traction cause the spidergears to seize om the cross shafts.

I should be right then, hardly any burnouts, should be good for circuit work then?

i'm not sure if the one i have is done, i think dunhams may have done it!
hope so. might have to ring to see what they actually do to them

I had one for more than 150,000k's...........no mods done to the diff and never had a problem