Lost 1000 Rpm
#1
Registered
Thread Starter
Lost 1000 Rpm
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.
#2
Geronimo36
Gold Member
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.
#4
Geronimo36
Gold Member
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".
#5
Geronimo36
Gold Member
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.
#6
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Thread Starter
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
#7
Geronimo36
Gold Member
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
#8
Registered
Thread Starter
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
#9
Geronimo36
Gold Member
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
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.
#10
Registered
Thread Starter
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.