prop id

[jeffz0rz]

this is the prop off my 22 foot closed bow sunrunner. i was only getting 53-55 mph at 4900-5100 rpm depending on water condition. my small block is good for 6500 rpm (cam, heads, roller rockers lifters ect) my vp 290 out drive has a 1.61 (i believe) gear ratio. my question is, do i go up in pitch, or down in propeller size to get at least in the low 60's ? there was another member on here with the same boat, out drive and motor (more or less) that was getting low 70's out of his boat. he hasnt been on here in over 2 years ive pm'ed the hell out of him.

seems it is a 14 x 21 prop. am i reading these numbers right ?

 

[steelespike]

Re: prop id

It does appear to be a 21" pitch.Were the engine mods designed for marine application?
Marine engines have a different power curve
If you read the stickies at the top of the page it will help you understand prop selection.
Your prop does appear to have a bunch of miles on it.You might start with a new 21" prop in excellent condition.You may need a change in prop design/material rather than a simple pitch change. I'm not an expert in high performance applications but it seems to me you should be turning more rpm with a 21" pitch.When you trim up does the boat respond.
Prop diameter change usually just follows prop design/application and is a secondary consideration.

 

[jeffz0rz]

Re: prop id

engine is marine built. the prop is eaten up bad. i guess all i can do is try to find the same prop in ss that will fit my volvo and go from there. thats the thing i hate most about props, you cant really tell what your boat will do until you try it.