osur866

Not wanting to hi jack, but what's the final ratio of a 1.5 lower with a 1.65 upper to be on a stand. Bravo 1??

Mr Gadgets

The 1.65 upper uses a 30/23 tooth gear set and the lower is the same as the 1.5, 15/19 tooth gear set.
End result is, 1.65 ratio, using a 1.5 lower with the 1.65 upper.

Does that make sense?

osur866

Yes, I have a 1.65 upper and changed lower from stock to a -2 Imco with a 1.5 XR gears and was curious of final ratio, thanks Dick for the clarifaction.

bobsbillets

Ok question ive asked alot of people and really did nt get a good answer. Say you have 800 h.p. and have 1.50 XR drive running 36p prop. Now you change gears to say 1.25 and run a 30p prop. Which is easier on the drive? smaller prop with a closer to 1:1 ratio or a larger prop with a 1.5 ratio? I would think smaller prop turning faster would be easier on the drive, but?

Mr Gadgets

Sorry to say, I have not experienced this situation, so I can not say exactly what might happen.
There are a number of factors involved with a change like that. The lower gear set changes in diameter somewhat and brings the two gears closer in size. But that does nothing for the weak point of net forged gears. The gears will start to flake off the outer layers of the tooth. And the teeth are all the same size between the lower gear sets.
The upper gear sets have the same issue of flaking. So to ask the difference in load in both situations, well if both props are theoritically the same, but just diffent pitch and you end up with the same gear ratio overall. There should be no difference. I didnt figure the numbers, but if one allows you to spin the drive faster with less pitch, it would be easier on the drive. (That would be the case in most situations, more rpm less pitch, less loading on gears)
But props dont seem to be the same when pitch is changed that much. There, I can not speak from experience. I have heard that there are favorite props in a series that favor one thing or another as pitch is increased. If the diameter of them changes, so does the equation.
Best answer is to find someone that has done it and see what happened. But all factors must be considered to lessen variables.
Sorry I cant be of more help.. the 800hp is the major factor in over stressing the gears and any time you get enough power to head toward bigger gears or props.. There just doesnt seem to be an "Easy"!

Hope that helps.
Dick

Panther

When I went from 1.50 to 1.30 my fuel consumption went up a bit and I lost 1-2 mph. I went down 6" in pitch and also the throttles were a little more touchy in rough water... I contribute this to higher torque loads on the engine with the lower gear ratio. Not sure if it's harder on the drive but I do believe it's harder on the engine (ie sucking more gas and quicker spool up when unloaded). Rule of thumb for me has become; run the biggest wheel with the highest gear ratio until you get into the Bravo I 34-36" props...

Back in the day the B1 (Pre-XR) 1.36 was rumored to be a stronger drive because the gears had more meat on them but with the XR's I understand that's no longer the case.