Prop Selection Help 175Hp Merc/Mariner

[Saltrunner]

I need a little help selecting the best prop for my situation. The Motor Power head is a 175HP Mariner and Carbs. The Foot came from my older Motor Mercury 150XR2. The Prop is a 22 pitch SSteel 3 blade. Its on a light weight 17.5 ft Glass stream bass boat. The RPM will reach around 6700 RPM Maybe 7000 at times. I'm not an expert on what RPM I should be turning but I feel I should be ok going to a higher Pitch Prop. My goal is to not blow the engine and at the same time get all I can from the engine far as top end. With the 3 blade 22 pitch that's on it now it will plane out in a second or two if I gun it. I also would like to know what difference I may experience If I put a 4 blade prop around 24 pitch. Do you think a 4 blade higher pitch may speed the boat up or slow it down? And would I expect a Rpm drop. What would be a safe RPM for this setup to not danger the engine? The engine is an outboard with the oil injection removed. The boat and original 150 Motor was 1988. Maybe I didnt leave out to many details if so ask me and I will reply.
Thanks,
S.R.

 

[Barnacle_Bill]

Re: Prop Selection Help 175Hp Merc/Mariner

Are you sure that tach is reading properly? Your max RPMs should be between 5,300 and 5,800 RPMs. If you are in fact turning 7,000 at times that motor must be screaming and that is not good.