Gear case ratio

[DangerNewb]

What's the easiest/best way to determine what ratio a gear case is? I have a 1990 200 Merc and wanted to make sure I know what the gear was for entry in prop slip calculators. Thanks.

[CircleHook]

put a tape "flag" on prop shaft and turn flywheel (assuming you still have lower on motor) Count rotations at prop shaft- Probably should pull plug wires....

[DangerNewb]

Thanks. So just count the rotations. Are there targets I'm looking for? 2 to 1? 1.87 to 1?

[FORBESAUTO]

To add a little note while doing the rotations. You will will have a good bit of rotational free play in propshaft due to lugs on clutch dog. So turn the propshaft so it's against the load side before you start turning the motor so that the propshaft begins turning immediately to get a god accurate count.

[DangerNewb]

OK. Will do. Thanks. Any input on what ratio/s I should be looking for. Normal increments?

[FORBESAUTO]

More than likely 1.87-1 or 2.0-1

[HStream1]

think of it as a clock. 1.87 = 1 complete flywheel rotation + another stopping at 10 O clock for 1 prop rotation. 2:1 = two complete flywheel rotations to one Prop. 1.62 = One complete Flywheel rotation + another stopping at 8 O clock to one prop rotation.


1.87 : 1 = 1 & 7/8 flywheel rotation. 2:1 = two complete flywheel rotations and 1.62:1 = 1 & 5/8 rotation to one complete prop rotation.

[DangerNewb]

Got it. Thanks for the info.

[Bullet 20cc]

These guys pretty much nailed it...don't know if your motor has all stock parts but the only other option would be a 1.78 ratio case Frankensteined over from an XR4 150hp. That would be 1 + 9 o'clockish. But you can pretty much tell if you have that case by the size of the bullet...4.25" diameter on the XR4 vs 4.75" diameter on all the other cases mentioned. I had one set up like that back in the day...was the highest ratio available at the time.

[DangerNewb]

Thanks Bullet and others. One very important detail I failed to mention. It has a Titus lower unit. Not sure if they were generally different than stock ratios? Not even really sure if it's a completely different lower unit or just mods to a stock? Thanks for all the info.

[HStream1]

If its a Titus Most likely its a coned Bass/Torquemaster unit at 1.87. I doubt its a Xr6 case unless posted pictures show otherwise.

Thanks Bullet and others. One very important detail I failed to mention. It has a Titus lower unit. Not sure if they were generally different than stock ratios? Not even really sure if it's a completely different lower unit or just mods to a stock? Thanks for all the info.