awsomethunder

anyway i could have lost 1000 rpm by switching drive from 1.50 to 1.36?had to replace my b1 and both drives have 1.36 on them.was thinking maybe someone switched gears in my old drive.

Panther

You'll loose RPM's by switching gear ratio's from 1.50 down to 1.36. You would need to re-prop. I went from 32" Bravo 1's down to 26" Bravo One's when I made the switch.

awsomethunder

panther do you know how many rpm's you lost when you made the switch?thought i had engine issues now i think it may all be from the drive change.

Panther

I really can't say that I lost any rpms because the gear ratio was different and I had to prop the boat to match. I changed the props before hand based on gear ratio and prop pitch calculations.

I was running 32" Bravo one's with the 1.5's so when I put the boat together with the 1.3's I got a set of 28" props and they were too big so I went with 26" props and spun the same RPM as I did with the 32's.


Here's a good link to play with the numbers... http://www.go-fast.com/Prop_Slip_Calculator.htm

Plug in your prop pitch, gear ratio, WOT RPM and top speed to figure out your slippage with the 1.50 ratio. Once you know your slip numbers, change the gear ratio to 1.30 and fool around with the prop pitch numbers until you get a similiar speed and that will give you a ball park for the right size prop that you need with a 1.30 ratio.

Rule of thumb I think it's usually 4" of pitch but on my boat I had to go 6".

Panther

Rule of thum is 2" of pitch = 300 rpms

So in your case 1000 rpms less is just about right if I had to go from a 32 down to a 26.

awsomethunder

well it's starting to make sense.the dealer is pulling my old drive apart weds to see what gears are in it.i bet its 1.50's.the bad part is i told them to order me a 1.50 and this is a good friend of mine.now who picks up the cost of the change over? do you think its ok if i just make up the diff with prop? may need to step down to a 21 or maybe 19

Panther

I honestly think you'll be better off with a 1.50 ratio drive on that boat. You'll get better throttle response, better fuel economy and more likely to have higher speed with the 1.50 vs. a 1.36.

awsomethunder

dealer just called,someone put 1.50 gears in my 1.36 housing.now we need to figure how where going to correct this issue.i feel i am covered because i told them to order a 1.50 in the first place.see what happens,least i know it's not and motor problem.thanks for the info

Panther

do you mean to say they put 1.36 gears in your 1.50 housing??

If you go from a 1.50 down to a 1.36 you'll loose rpm with the same size prop. If you go from a 1.36 up to a 1.50 you'll gain rpms.

awsomethunder

my old drive was marked 1.36 but had 1.50 gears inside.so when we ordered the new drive they ordered 1.36 even after i said i wanted 1.50.didn't know the difference between the 2 was that much.