PDA

View Full Version : How bad is Slightly overpropped?


Bobwire
09-05-2011, 08:18 AM
Its a 09 MCX 350 MPI in a CSX220. Im running a 13x14.5 4-blade. The motor spec calls for 4800-5200 rpm range. I barely get 4800. If im loaded down pretty good i can only get 4650.
Would this be concidered "slightly overpropped"?
I know that ideally it should be in the mid to upper range, but It jumps right up on a plane no problem, and i like the cruising speed it has.
Am i going to kill my motor running it like this?

Thrall
09-05-2011, 12:35 PM
You're slightly underpropped. No it won't kill the engine and you can't get much lower in props pitch for your application. It should rev out to 5000 or more I'd think.
Maybe there's a performance issue with the engine??

TRBenj
09-07-2011, 01:57 PM
You're slightly underpropped.
No, the original poster is correct. He's overpropped.

A prop with too much pitch = too few revs, and thus overpropped.

I would think that propping down slightly in order to turn 4800-5000 in all conditions would yield the best performance from the boat (and likely boost efficiency as well). But, 150-200 RPM off isnt huge either. Your call on whether you feel justified spending the $$.

Thrall
09-07-2011, 09:19 PM
trbenj, makes sense now. My mistake.
Is it really a 13x14.5?
Sounds a little weird. Not a prop OJ lists for your application and not one I'm familiar with.
SOmething like a 14.25x14.5 would seem to be the better application based off of same and similar hulls, but get ahold of OJ or Acme and they'll steer you in the right direction.

willyt
09-08-2011, 10:10 AM
yea... agree the prop specs dont seem right. I'm not extremely familiar with the CSX line, are you sure you have a gear reduction transmission? if its a 1:1 or a 1.26:1 its going to change everything.

Thrall
09-08-2011, 12:05 PM
That's right, forgot CSX's are Direct drive.
Would imagine it's reduced, not 1:1, as that's ALOT of boat for a MCX.
Bobwire, find out what the gear ratio is and call one of the prop guys mentioned.