Under propped now, need help ASAP

[Xesvuli420]

I have a 13 1/4x3x17p Michigan SS(I think) prop now on a OMC/Cobra 3.0L 4cyl 140hp Drive. This prop makes an excellent ski prop, but I am now looking for a Speed Prop.

Currently I can only go about 3/4 throttle before I max out the WOT range (4200-4600rpm)

I plan on getting an aluminum prop (because I hear SS is really only an advantage as far as speed after 50mph), but I need some help before I buy.

Should I go 3 blade or 4? What are the benefits/sacrifices?

Would a 21p prop most likely allow me to WOT correctly?

What difference will changing the diameter have? I might have to because of availibility. I may have to go down as far as 12 1/4.

I plan on ordering today. I have tried reading the tutorials of prop picking, but they all say different things, and are confusing. I would much rather have your opinions.

Thanks everyone!

 

[steelespike]

Re: Under propped now, need help ASAP

It should be ok to do a brief test at wot(wide open throttle).
So you could get a max rpm.
When changing materials makes it difficult to estimate the changes.
But a good 21" aluminum prop should improve your top end with a less hole shot.A 4 blade would help retain your hole shot with a slight drop in the improved top end.