Motor Change, new prop size

[mike165]

Just replaced the L6 in my 20' bayliner tri with a 350ci Vortec 330 H.P.,have two drives 1.1.65 and waiting for a set of 1.1.50 gears to go in the other box,gave it a run with the 1.1.65 and 141/4 x 18 3b ss, seriously high revs 6K+ what prop would suit when I get the 1.1.5 box on

 

[Maclin]

Re: Motor Change, new prop size

The rpm's would be lower for any given attainable speed when going to the 1.5 ratio drive.

Using 6000rpm and 10% slip as baselines for an 18p with the 1.6 drive, we get 57mph theoretical speed. With a 1.5 drive and all those same numbers and 18p the RPM's would be at 5600 at 57. Using all the same numbers with a 1.5 drive and a 21p the rpm's are at 4800.

With the 1.5 ratio drive I would start with a 21p and do a water test to see what RPM's the engine can get to then.


There are a few posts here with prop calcualtors in them, some have a formula and some go to a website. You can also search the web for info and calculators. Here is a website I use and it produces good comparison numbers...:

http://www.marksmarineinc.com/prop_calc.aspx

 

[mike165]

Re: Motor Change, new prop size

THANKS for the informative reply