Sporty 1.75 gears vs 1.62 gears

[Strokerdean]

I run a 300xs/sporty/1.75 gears and run anything from a 28p to a 32 p prop depending on what I am doing. Just wondering what is easier on the lower unit and gears, 1.75s with a larger prop or 1.62s with a smaller prop. Maybe it doesn't make a different.

[ThunderCat]

that's a great question dean... i would want to know myself. even though i can't run a 1.62 case.

[Strokerdean]

Seems like the 1.62 would be easier on the lower with a smaller prop but the 1.75 gear should be thicker than the 1.62 and be able to handle the larger prop. That being said, I have heard of a few guys breaking a prop shaft trying to run a big wheel with lots of H.P and a small prop shaft.
Someone has to have a coment on this topic, again just wondering what this group thinks as I have the 1.75s and not planning on changing because of the prop selection I have.

[EuropeanAM]

Dean:

It actually depends on the BOAT and setup. Some may run better with the 1.75, others with a 1.62.

Also depends on the engine. I have guys running 250XS with 1.62 ratio on Strokers, and also 1.75 with a 300XS.

The PRIMARY reason to change the ratio is to bring the propshaft RPM's into a range where a SUITABLE prop choices are more readily available.

Example: If with your setup, you're running a 1.75 ratio Sporty, and are hammering the limiter constantly with a 32P prop... a 1.62 ratio gearcase would get you back down to the 29-31 pitch range, while remaining within recommended RPM's.

The same above theory can be applied to help keep the engine within it's PEAK horsepower and torque curve. For instance, though most of the 3L-XS models will turn 6300 (or even close to 6400), their actual "peak" propshaft output is often found in the 5850-6100 range. Gear ratio can be combined with prop choice to help bring the engine "into" range (and widening the selection of suitable, available propellers).

So there really isn't a single-application answer, other than the general rule of thumb is that, the HIGHER the prop pitch, the more strain on the gearcase/driveline.