Yet another prop question -- 4.3L OMC Cobra...

[canadianguide]

Hello...I've got a 91 4.3L engine with a Cobra Sterndrive in an 86 Baja Islander 180 boat.<br /><br />its got a 14 1/4 x 21+ prop on it right now, and at WOT I only get 4000rpm. Another thing is that if I put a guy at the very back (ie on top of the engine compartment) It will not plane out. I only get 3000rpm at WOT until it planes out, that is IF it planes out. What should I do?

 

[achris]

Re: Yet another prop question -- 4.3L OMC Cobra...

Get a prop with a smaller pitch, before you cause some serious engine damage......

 

[buddyx1]

Re: Yet another prop question -- 4.3L OMC Cobra...

Try a 19+ prop. I have a 18ft MonArk '87 4.3l Cobra and do not have any problem with 7 people in the boat 4 adults and 3 kids close to 900lbs and have no problem plaining out and getting around 40mph WOT at about 4100rpm. It does take a little longer to plane out but still not a problem.

 

[Boatin Bob]

Re: Yet another prop question -- 4.3L OMC Cobra...

Yes...go with a 19, rule of thumb is approx 200 RPM for each in pitch you cahnge so a 19 should give you around 4400, much better for that engine and you will notice an improvement in your hole shot, might lose a little in top end. If you are going to do any skiing or wakeboarding you might even consider a 17 but watch your WOT RPM's don't go too high.

 

[canadianguide]

Re: Yet another prop question -- 4.3L OMC Cobra...

what about the diameter? should I stay 3 blade?

 

[buddyx1]

Re: Yet another prop question -- 4.3L OMC Cobra...

14 1/4 and 3 blade is what I am using, but I have not tried anything else. Let us know what you end up using and any performance difference you get.

 

[motox6]

Re: Yet another prop question -- 4.3L OMC Cobra...

I'm running a 15x19 pitch on my 5.0 OMC. Getting 4500 RPM