Re: outdrive info
That's actually a long and complicated answer, but to try and keep it as simple as possible...
The 'plan' is to keep the prop for the engine/boat combination in the 15" to 21" type range.... The smaller the prop pitch the less efficient the propeller, so towards that higher end is better...
The ratio is determined by the most likely size of boat the engine would be put in... The 2.5 and 3 litre engines ended up in smaller boat (obviously), so need a higher reduction to turn the mid-size prop. As the power increases the boat that the engine is likely to go in also increases and the maximum speed also goes up, so the drive reduction needs to be lower, again to keep the prop in that mid-range.
Your boat is quite large for the engine power output... You would almost be better going to a HIGHER reduction, like a 1.65:1 drive... That will get you into the higher pitch props and the boat will feel better.
A few years ago I changed engine, from a 1994 4.3LX with a 1.84:1 drive running a 21" prop, to a 4.3MPI with a 1.62:1 drive. I should be running a 19", but the mid-range is so bad with that prop that I'm running a 17"... The new engine is more powerful than the old, but the drive ratio change has completely negated that. Although I am about 4 knots quicker, the boat felt better with the 1.84 drive. The next time I change engine, I'll be going back to a 1.84:1 drive...
HTH,
Chris......
. The other one, the 6152290 looks exactly like this one, with the larger trim cylinders and squared vent plate. 
. But yet you say you look up the numbers and it says that its an mc-1. THE first one is an mc-1, the one with the eyehook. This is where I am confused on how merc categorized these numbers. AND both drives are out of v-8. The 478 one is from a 228, and the 615 is from a 260. Now, on the 615 drive, I did see some numbers stamped on the case, and the were "R 1.32. So im thinking you could be correct on that ratio. Could I put that unit on my 228?
