why2dogs

I am converting a 302 Formula from TRS to Speedmaster III. I was going to maintain the current crank shaft center for the Speedmasters. I have since been told that the Speedmasters need to have a higher drive height. Somewhere in the order of 1 1/2 to 2 inches higher than the existing TRS. The reason I am told is that the SSM is a "semi-surface piercing" drive. If I leave the drive at the same heaght as the TRS, I would have to trim the heck out of them to get the performace I'm looking for, if at all. Can anyone out there agree or disagree? Thanks!!!!

CIG3

I would agree that the #3 ssm is deeper than the TRS, about 2 1/2 inches. I dis-agree that it is a surface or semi-surface drive. If you mount the #3 in the same location as the TRs you will have serious drag issues. My suggestion would be to go up 1 inch higher than the TRS.

why2dogs

I like the thought of only raising the drive about an inch. I'd like to keep the weight as close to the keel as possible, and I really want to avoid clearance problems with the factory hatch, transom exhaust locations, swim platform, etc. Thanks for the reply!

Pismo10

Wasn't the SSMII, 2 that is, a direct replacement for the lower unit of a TRS? That would be nice to find, easy swap if true.

why2dogs

Yes the SSMII was a direct fit on the TRS upper. The SSMIII is way different. The drives are larger and much heavier than my old TRS. I can testify after carrying them into my garage. It has a much larger gimbal assembly, too. I have already purchased reconditioned SSMIII units, so I'm into this project with both feet. No looking back now. Thanks for the reply!

why2dogs

Hi CIG3. I called Mercury Racing Division to ask about this. They tech told me the crank shaft centers are within 1/8" of each other (trs and ssmiii), and that I would be OK mounting them at the same height. I have several other sources telling me to raise the drives anywhere from 1 to 2 1/2 inches. I'm guessing that these sources are talking real world experience and Mercury is quoting scripture from the manual? Any information you can pass along would be a huge help. Thanks!

IRONMAN

Are4 the new units 3's or 3A's That may make a difference in your decision, same length but diff prop possibilities.

why2dogs

3's

CIG3

From a straight up length difference, Mercury is correct. But from a drag aspect the #3 has more due to the length and mass of the lower. Also remember that you will be running a differant prop configuration that gives you much great bite than the old clever or bravo style prop you are running with the TRS. This all factors in. The one inch up is very conservative as I don't know your power combination or how you use your boat. Two inched wouldn't hurt you if everything would still fit under the hatch as you want.

rdoactive

The III at the TRS level will be slower. The lower is bigger and the IIs props are more efficient as semi surface piercing.
1" up is VERY conservative. Most old TRS boats could run the TRSs 1" higher and go a couple mph faster.
If you can, raise it 2".
It might be worth checking out SSM drive height on similar size V hulls before you recut your transom.
Gary