gear ratios

[david1young]

can any one help
i have a gear ratio 28/38 on jet
it should be 36/30 on a boat of 3300lbs
28/38 is for v8 petrol 5000 rpm
36/30 is for 200hp diesel 3300 rpm which i have but boat 6500 lbs
a gear set it very expensive and before i buy i just would like to understand
what is happening and if the gear ratio being wrong is helping or hindering as the boat is over weight
now the seller of the gear set says my set up is only producing 58hp not
200hp
yet the boat will do 21 knts
my engine if aloud to will run to govener 3900 rpm
the gear set is £500.00, $1000.00 what is the effect of changing to
36/30 going to be
thankyou kindly for reading this and any relpy i may get

[jim lee]

Boat weight has no effect on your jetdrive/engine setup. Gear the pump to where your engine makes its max horsepower. Anywhere else and your missing power.

Do you know at what RPM your engine makes its maximum horsepower?

-jim lee

[david1young]

thankyou for taking the time to reply
my engine has max power at 3300 rpm continious power 3100 rpm
gear ratio is 5000 rpm

[jim lee]

And you can't work a deal where they let you try the different gear set to see if you like it or not?

The jet drives I've delt with (Berkeley kind) you trim the impeller to set its max RPM. On those pumps using a gear set didn't really gain you much.

-jim lee

[david1young]

castoldi only come with one impeller then every thing is matched through
the gear box that is if you have the correct size jet for the boat
there is only one dealer and it is do you want gear box or not
so i have brought it fingers crossed i guess if the gear ratio i have ony gives
max power at 5000rpm and my engine only produces 3100rpm i am losing
a lot of power?
regards david

[jim lee]

As for loosing power, you have to look at the RPM/HP curve of your engine to decide that.

Good luck!

-jim lee