#4 Speedmaster Gear Ratio
 

As most of you know gears for the 4 & 5 uppers are hard to come by: Question, someone rebuilt a upper using a 16/21 gear count = 1.31 ratio, the other upper is 15/20 gear count =1.33, lower on both 1.125.
Being the power is evenly match, has anyone used a ratio this close and was there any RPM spread, the props are matched and ran even RPMs prior to this. Maybe I am splitting hairs, matched gear sets are like props and matched engine power.

My guess is it would be a minor variance, very minor. maybe 50rpm? But, just a guess.

i agree,most marine tach,s it would be hard to see a 50 rpm difference from one to the other,and engine load will be almost identical.

That's the question, how much? By the time you figure slip.
This is on an older 33" Executioner, came with TRS back then, changed to #4 back 8-10 yrs ago. X # was in the TRS location. It has been moved up about 2 ", so now we changed everything. Same power 780 @ 6200, now the RPMS will increase and 1 drive is slightly different. I know the props will need some tweaking, but now the props will have to adjusted for gear ratio.

If you have a chance; check all the different ratios that were available. The gear counts are close. Why would MERC offer so many ratios?

gears
 

if you want answers to you questions call craig corabella of corabella performance he was aperformance drive guy at lake x really knows thoose drives

Is it standard or counter rotation? We need the details to solve the mystery!

I spoke with Craig, back at the beginning of this. I called; him to find out if he had some 1.33. The gear that is a 1.31, is from the guy; that purchased the molds and tooling from MERC. I was just trying to get a heads up on the difference in RPM, the drive guy's answer is bend the prop. My customer would have had no problem buying a matching gear set for the other. It's just screwed up to me. Guess we will what and see.

You have been out of town to long! Get some rest over the weekend, and ask me that question Monday

Wasn't it your boat, the one that someone installed the drives on up-side-down, that you had to drive it with scuba gear on??

1.31
 

I hate to disagree guys but the gear ratios need to be exact.:party-smiley-004: Years back a friends boat had 1.58 on one side and 1.50 on the other. It never handled right and would sometimes roll side to side(the diff was only a couple hundred rpm)....guess what fixed it? The next winter he had the uppers matched up and she tracks straight well past 100mph now. The difference in acceleration from side to side I believe can mess with a boats ability to "set" correctly. just my.02. I also have seen super fast skaters dial in some handling issues by adjusting throtle cables to pull exactly even. Your 1.33 upprer has helical cut gears for the #3 and #4. Your 1.31 drive has the stronger #5 straight cut design that GK makes to put in the older SSM's. Guess it all depends what you are doing. Good luck.