My boat came with a 14 1/2 x 24 Raker prop. That's all I have ran on it. It also came with a 4 blade prop that is a 13 1/4 x 27.

If I switched to the 4 blade...what should I expect?

19' bass boat with Johnson 150 Fast Strike 150hp

You should expect it to be way slower because I doubt you can turn a 27" prop.

Even smaller diameter prop?

Props can be confusing, diameter, pitch, rake, cupping...all make a difference.

Easiest way to understand, that pitch number is how many inches of forward travel it would move with one rotation. Think of it like gears in a truck. Your goal is to prop so at WFO you are running at the TOP of your motors RPM range. Right at.

Too low is just as bad as too high, your holeshot suffers, and you're putting unneeded stress on your bearings.

There's a lot of knowledge here, if you want good answers, ask good questions. WHAT boat? Jack plate? What height? And most important, what's it doing now? Speed? Rpms? Holeshot time?

That 27p sounds like a shooter. the old theory of 200 rpm's per degree of pitch doesn't actually appy
in comparing those 2 props.

however, like pat said.. its not really possible to give you the proper advice with out knowing what the 24 raker is
actually doing.

best thing for you is.... go run it!

be sure to change thrust washers, as those 2 props don't use the same one.

My Raker will go 5000-5100rpm - 62-63mph

Boat is 1994 javelin 389T 18'9"

What thrust washer would I need?

Have the Raker worked. You're low on RPM's. Need to turn 5400 to 5500 at WOT. Ditch the 4 blade

I may can get it that high. I havent ran this boat anywhere where I can run it wot for a long period of time.

I dont have a jackplate either.

I don't see you being able to turn that 27.

Your homework for today: Go run it as hard as it can go, FULL throttle, FULL trim, and see what it does, UNTIL then, nobody will have the slightest clue what to do.

I have a 17'9 ranger 150 with same prop I can run it on full pad at 5500 to 6k rpm. I don't think you can turn that 27 and be happy.

no jack plate .Runs close to 70 mph gps.

you have the raker?

yes

ill go check exact but believe it's same prop remember 87 boat so lighter probably