As an Amsoil dealer I cannot resist the opportunity use a “lube thread” to do some selling.
I agree with everything that Ranger said. Particularly the parts about ZDDP and the fact that most oil companies formulas change regularly driven by mostly marketing more so than engineering. Honestly, I think that such decisions are driven mostly by accounting. Saving a couple of cents per quart of oil on a less expensive additive package can drop millions to the bottom line for the big oil companies.
I have been using Amsoil for more than 10 years. I got started based on the testimony of a fellow racer that stopped burning up 944 gear boxes once he switched to Amsoil gear lube. I was racing a 944 then too, tried Amsoil gear lube as well and liked it. In my early years with Amsoil I did dyno tests, studied many used oil analysis reports, even penned a technical article about synthetics. I have also read quite a few articles penned by Charles Navarro who is big on high levels of ZDDP for engines like ours. I agree with Charles findings but disagree with the brand he likes (and sells), Brad Penn AKA BP. BP has similar levels of ZDDP as Amsoil’s higher line oils but BP is a group II petroleum base stock. Amsoil uses a group IV PAO synthetic base stock which flows better when cold and is more stable at high (250-350F) temperatures. I have stuck with Amsoil as I believe we need the benefit that synthetics provide, after all of my study I remain convinced that they are committed to be a step better than the rest, and as a dealer I get incentives to use and sell it. I am admittedly and unabashedly biased.
I am currently running the 15W50 Dominator racing oil but plan to switch to the 10W30 racing oil. I don’t have the guts to try the 5W20. I do use the MTF in the tranny and 75W90 Severe Gear lube in the diff. I mentioned above that I have done some dyno testing and this combo of lubes does allow about 3-5 hp more to the wheels than common petroleum oils. I have not tested BP or Redline oils to see which combo provides the best HP to the ground. Some say that Redline delivers the most power but I honestly do not know.
The following link has some info on the racing oils;
http://www.amsoil.com/a/synthetic-motor-oil-engine-oil
The following links have info on the Tranny fluids and gear lubes respectively;
http://www.amsoil.com/storefront/mtf.aspx
http://www.amsoil.com/a/synthetic-gear-oil
One more thing, I offer dealer cost to all Spec E30 racers and in some cases free shipping. PM to ask me how this works.
Don