We are putting about 900 HP through a 1.7-1 ratio #3 drive with 520 blower motor at 6500 rpm. That is the life of the drive with that amount of HP. Only gota 14.5 X 21cleaver stlye prop so there is a bit of give there. Jas

With a low gear ratio like that, shouldn't you be running a bigger prop? I would think you are taxing the drive a lot more by by running that 1.7. A 1.5 or even a 1.3 and I would think your drive will be happier.

i talked to doller marine and they had a boat with 900hp sc engines in front of #3's and never had a failure, they ran it hard for years. if you should break something find some #3a lowers and your good for 1000+hp

What kind of boat?

what is the diff between #3, #5 drives just more HP allowed?

the 3 is a taller drive than the five. my cig is rigged with threes its a 79 yr boat. the motors are very high in the hull to get the x dimension where it needed to be for performance. the five is 5 or 6 inches shorter so you can keep your cg lower by mounting you engines in a much lower position in the hull. the three and five have different prop shaft sizes the #3a and the five have the same size prop shafts. the uppers i believe are the same as far as gear and shaft sizes. a 5 and 3a are each conservatively rated for 750 hp but a several guys are running 1000 to 1100hp in heavy boats with them with no breakage. 3a's, 5's, and 6's use the same props. im upgrading to #3's lowers when i put in my blower motors so i wont have issues. i will be selling my #3 lowers and props when i do.