new motor, same old prop, need advice

Kegler

Recruit
Joined
Jul 28, 2003
Messages
3
I have a 21' 1981 Searay Cuddy Cabin (a very heavy boat) that had a 260 Mercruiser I/O. I got the boat for free because the motor was shot. I rebuilt the original 350ci engine, bored it 60/1000 over and put a stroker crank in it with new high compresion heads and a marine cam. Also replaced the Rochester four barrel with a holly double pumper 650cfm. It is 10.7:1 compression so I am running 94 octane fuel with lead substitute. I have taken it to the water a few times and it runs great with a good hole shot, but the top end is only 34 knots at 4600rpm. I know very little about props so I asked my local sport shop about it. They told me that I had a 18 pitch prop and the next step up would be 21 and that would be too much for the motor. I find it hard to believe there is no in-between prop for my situation. I can have 6 people in the boat and pull 3 skiers simultaneously and it does not work the boat very hard, but I am wondering if it could do better. I have never changed a prop before, I believe the one I have is stainless steel. Any advice would be great. Thanks!
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: new motor, same old prop, need advice

Moving this to I/O and inboard.
 

Doug Durako

Chief Petty Officer
Joined
Nov 17, 2002
Messages
519
Re: new motor, same old prop, need advice

Cool setup.<br /> <br />There are props of every pitch from 18 to 23 that will run on your rig. Best prop is one that gets close to the max rpm on your engine at wide open throttle and also gives you a hole shot you can live with.<br /><br />Find a good prop shop and test a 19 pitch, 21 pitch, 22 pitch, etc., or borrow from friends. That's the only way to tell before you invest another $500 in a new stainless steel prop.<br /><br />I get a great hole shot and about 63 mph at 4800 rpm with my original equipment mercury quicksilver prop. My boat is a lot lighter than yours, but you should be getting better top end.
 

magster65

Commander
Joined
Sep 1, 2002
Messages
2,573
Re: new motor, same old prop, need advice

You should definately go faster. My 23' SeaRay with a 305/2V merc went that speed. Try a 19" or 20" prop first. A rule of thumb is 200 rpm per 1" of pitch (an inch of prop diameter is almost the same). You'll want to keep a healthy 350 around 4300 4400 rpm at WOT.
 
Top