gear ratio combination
 

Any body can tell me where to find the end ratio of a xr 1:50 and swap the lower for a 1:36 ?

thx

Here's a link to a chart.

http://www.mtboats.com/outdrivegearratios.html

that makes everything clear ,

thank you

I don't have my drink on........Can someone tell me which tooth count is a 1.35 lower? I am looking at doing this change also. THANKS

The 1.346 ratio lower gears would be 15/17 teeth. if used with the XR 16/19 upper gears.

With the 27/32 B1 uppers, the ratio would end up being 1.343.

Mr. Gaget, What are the advantages/ disadvantages to running the 1.34 lower with a standard 1.50 B1 upper? I'm not putting any big H.P. through them(500). Also what is your thought on a sportmaster lower, as far as strength over an Imco. I think from reading a few articles that the upper will be weaker?! Thanks, Rob

can you put a 150 lower on a 136 upper??? and can you put a 136lower on a 150 upper is this possable????

Rob,
I dont see an advantage to going to the 1.34 lower when running lower hp. You would end up with smaller pitched props but it is usually a disadvantage. The lower gears are more costly when using 15/17 lower gears. Most common run is the 1.5 ratio untill you run out of prop.. Used to be the 34 pitch and above were not great, but I dont believe that is the case these days. But with low power you shouldnt even get close to those big pitch props..

Bajabob,
you can put any gears you want in the B1 if you try hard enough. The end result:
1.50 lower (15/19) with the 1.36 upper (27/29) will give you an overall 1.36 ratio.
1.50 upper (27/32) with the 1.36 lower (15/17) will give you 1.343 ratio. So you can't actually call the (15/17) lower gear set, the 1.36 lower..
Hope that makes sense.

Dick

I am building a litlle 21ft v hull normally whit eagbeaters on them but I put in a ls 2 all alluminium corvette engine in it whit estimaded power of 550hp .

I prefer a smaller prop because of the very light weight of the boat (2000 lbs ) so it doesn,t effect the handling to much

and the shorty is to keep the engine as low as possible .

thanks dick i have a spare lower for my bravo . it a 150 . i now have a 136drive on my baja now i am runnig in the low 80mph with a 23mirage prop

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??

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? :)

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.

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?

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

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.