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What is the current state of the art for gearbox lube suggestions?

Redline super light

Redline 75w90 is also fine and Superlite is actually rated at 75w90. On a Vee trans you don't need the Shockproof stuff, but it won't hurt.

Reline specifies Superlight as 70W/75W. The viscosity is actually 1/3 that of 75W90. It is the lowest viscosity gear lubricant available I believe.

My research indicates that a FV gearbox will hold up with an oil 1/2 the viscosity of Redline Superlight. Lower viscosity means less power loss but more wear.

Brian

So would it be feasible to run a staight 50 weight motor oil, or does gear lube have certain specific gearbox-friendly additives?

Greg,
You should only use a lube with EP (Extreme Pressure) properties. That is the basic difference between regular motor oil and gearbox/diff fluids. .. so .. NO - running engine oil in the gearbox is a no-no.
Just go to Advance and get a couple quarts of gearbox oil.. or you can use ATF if you want something really light weight, but the wear factor will be higher - mostly showing up on the paddles, side-gears and fulcrum plates (expensive and time consuming to repair).
Steve, FV80

Steve is correct. You need an oil that higher shear strength properties. On the other hand you want a slightly lower "weight" for a racing box. A 75w90 is fine (verses 90W140 etc.) and there are many versions of it. (Many synthetics, Redline MTL, MT-90, etc.)

A synthetic has a better "pour rate" when cold. So a synth 75w90 give you more HP in the first few laps of a race. (You can actually see this on the chassis dyno) When either (synth or base stock lubes) reach 140 or so you can't really tell the difference.

better yet, go out and buy some motorcycle synthetic oil. It's designed to work in a engine/tranny and surpasses most auto oil.

Thanks to everyone for all the input on my question.

I want to second what Steve said (FV80). You should run something EP rated. It's the ring and pinion that requires the EP rating which straight motor oil will not have. Lots of plain transmissions ran/run motor oil. The original Mini ran the motor oil AS the gear oil (not always a good thing, but for other reasons...). It used a helical gear set rather than a hypoid ring and pinion. The reason you need an EP oil is that there is more slip in a "hypoid" gear set like in a diff than in normal helical gears. We also have lots of slip at the fulcrum plates which for me has always been the weak spot in my transaxle.

Could you get away with something else for racing? Probably, at least for a while. But maybe the lack of EP rating would actually increase friction (and thereby wear) enough at the diff (and fulcrum plates??) to make up for any advantage gained in the rest of the box. The point is that the "correct" oil for anything with a "normal" ring and pinion is an EP oil, designed for use with hypoid gears.

Been a few years, but remember when VW had their automatic stick shift? VW tranny with a torque converter? Ran ATF from the factory.

It is the high shear from a hypoid gear which requires an additive, often molybdenum disulfide. That's why older gear oil stunk so bad. It's a balancing act..you want adequate lubrication to prevent wear and galling, but if the lube is too slippery the synchros won't work as well.