RPM Difference
 

If you had a 30" prop on a standard Bravo 1.50 drive turning 5000 RPM's. What would be the RPM's with the same prop but with a 1.36 gear? I'm just looking to compare the RPM difference between the 2 Ratio's.

about 1000rpm. If it turned 5000 with a 1.5, then it will turn about 4000 with the 1.36. You would need to drop down about 4" of pitch to turn the same 5000 rpm with the 1.36.
Eddie

also I would stay with the 1.50

actually i think the math says about 514 revs so more like 4500 all things being equal. i.e to say that the motor has the power at 4500 to pull the longer gear to the same top speed.

About 600rpms.

here is a link for you to play with
http://www.rbbi.com/folders/prop/propcalc.htm
I have used it alot, it works pretty good
larry

Not going to change the ratio, trying to figure out whats going on. Suppose to have 1.50 drives boat, but only turning less than 4000 rpms. This boat should be turning 5000-5200 rpms with a 30" prop. Dealer changed lower units on Bravo drives so the serial number will not match up with ratio.

Why don't you just take the drive of,put in gear and turn the input shaft,,that way u know for shure what u have.

Input shaft 15 rev. / Prop shaft 10 rev. = 1:50 !!!!:cool:

Good ieda, Boat right now in shop for some other issues so I'm going to have them check for ratio also. Just trying to get some info so I might be able to talk with a little knowledge to the shop.

there are a million things that will cause that....

are you saying it USED to do that and now won't or that this is a new motor / boat combination that seems to be under performaing ? seems to me that you should be able to post all your specs... length, beam, type of hull, esitimated hp, drive type and current prop and someone here is going to say " oh yeah, ive got one of those and this is what it does...

i remember getting my boat together for the first time and couldn't see the speed or the revs that it should and without changing any hard parts, but just trimming and dialing things in went from 4200 rpm to 5400 rpm. what i had was a couple of knowledgeable people telling me that their identical combination went 60 mph... so why was mine going 45 ? was just mistakes i was making in set up and operation...