Way back when, there was a thread about the various "number" drives over the years, but I can't seem to find it (it was a long time ago). So, a new thread on the same subject...

What is the difference between a #3, #3A, #4, #5 drive? I see the #6 is still for sale on the Merc website, so I know what they are all about, but when I cruise through the classifieds I think I'm back in Sister Mary Rulerknuckles math class

And what happened to driver numbers 1 and 2? This stuff is as confusing as the APBA class format....

I'll give it a shot. Hopefully the experts will be able to fill in the holes or correct my mistakes. BAM how aobut it?

#1 I think is the Alpha SS. NLA. I personally don't consider this a true speedmaster because it only uses one drive shaft in the lower unit. I think it is just a shorty Alpha case maybe 350 HP on a light boat.

#2 is a TRS upper with a speedmaster lower case. NLA and parts are getting hard to find especially for the RH models. Handles the same power as the standard TRS, MAYBE.

#3,#4 NLA. Share most of the same internals, but the #4 is 6 inches shorter than the 3. The 3's and 4's have prop shafts with 19 splines are 1.25 dia, and had 4 or 6 inch long prop shafts(short or long shaft). The later fours came with the bigger prop shaft of the 3A, 5 and 6. #3and #4 are rated to about 750/750 although I know several people putting a LOT more than that through them.

3A,5 have the same internals the 5 is 6 inches shorts than the 3A and all have the big prop shaft. I have heard rumors that the #5 is no longer being made. Don't know about that though.
Handle about 900/900, again there are units handling a hell of a lot more than that.

The #6 is the #6 don't know much about them.

All need transmissions. The cool thing about the speedmasters is to keep the lower case narrower, they used two smaller drive shafts to transfer power to the prop shaft. Check out the BAM marine site for the fische pics.