what kind of prop should i use pitch and all that

[catchingmore]

i have a 1990 4.3 invader little over 18 ft long it is a alpha one max rms are 5200 give or take a little i am trying to find the right prop for it the one on it is beat up from previous owner i am doing about 42 mph if i could gang a little that be great if not i like to keep it the same thanks for looking i am new to the i/o's

 

[ctgmopar]

Re: what kind of prop should i use pitch and all that

Hi, the prop you have on there should have a stamped number....example 13 3/4" by 17", If you follow the number & buy the same prop size you should get the same results you are looking for. This simply means the prop if it were moving on a flat surface would move 17 inches for every 1 revolution. multiply that by your rpms & you get your total distance you can cover. Hope this helps.
Chris

 

[whit71]

Re: what kind of prop should i use pitch and all that

I would be careful 5200 RPM is a little high for a 4.3 I wouldnt run it over 4400-4600.

 

[steelespike]

Re: what kind of prop should i use pitch and all that

Hi, the prop you have on there should have a stamped number....example 13 3/4" by 17", If you follow the number & buy the same prop size you should get the same results you are looking for. This simply means the prop if it were moving on a flat surface would move 17 inches for every 1 revolution. multiply that by your rpms & you get your total distance you can cover. Hope this helps.
Chris

You need to figure in the gear ratio to get the actual prop rpm.if 2;1 motor turns twice prop once.
Also typically there is prop slip as well that reduces the overall effect.

 

[180shabah]

Re: what kind of prop should i use pitch and all that

WOT for that engine is 4400-4800 so your are over the max by 400rpm+/-

That drive SHOULD be a 1.84 gear ratio, but after 20years anything is possible. If the gear ratio is correct, I would guess that you have a 19" prop on there and stepping up to a 21" (or + 2" from whatever you are running) wil bring your RPMs back in line.