I should soon have my shiny new Quaife ATB in my 3.38 7" Sierra diff.

I know it only needs normal EP90 oil as the Quaife diff is an ATB not an LSD that requires special oil.

However I'm sure I remember reading a lot of the RGB boys run fancy Red Line diff oil as its claimed to reduce transmission loses etc.

Something like this:

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=400011054735

they do a few different versions.

Or I may just go for the Silkolene stuff that Quaife recommend:

http://www.quaife.co.uk/Silkolene-Silktran-SYN-75W-90-synthetic-gear-and-transmission-oil-per-litre

I guess that might be the safer option rather than going for something too thin in the search of 0.01 bhp

I've got the Superlightweight stuff in my diff. It's amazing smelling stuff!! I think in my diff I probably need lightweight rather than super as it crashes a bit when taking up the backlash, I suspect if I had thicker oil it wouldn't do that. I also had a problem with the diff oil escaping as vapour via the diff breather. In the end I put a long breather hose on the end of the breather nipple and that stopped it.