Mercruiser 488 RPM Full Throttle

[cajun1957a]

I have an early 70's - 17' Tempest with a 488 Mercruiser engine, Quadrajet Four barrel carb and a 17P High five Staneless prop. The motor runs fine and after a rebuild kit to the carb a year ago, the lean sneaze I had appears to be gone. I know this is a heavy old boat but with the set up I have, the best RPM I can attain is about 4000 w.o.t. This is about 30+ mph and thats fine. I took it out today and had my wife, my self and four grandchildren from 15 down to 8 years old. Im figuring for sure I can get more out of it with less weight. What RPM should this motor run W.O.T.? Assuming its trimmed right. I also have dolphins on the out drive. the High5 prop I got really cheap and it pulls fine. I had a 17P four blade on it as well and seems to work the same.

Randy

 

[alldodge]

The fins can help get you up on plane but also create drag. Everything in the water creates drag and while there may be some benefit, they all slow the boat.

17P High five

Again, the more blades, the more HP it takes to turn the prop. The 5 and even 4 blade props take more HP to turn. the more blades can create lift, but if the boat is not fully up on plane this can be a loss in performance.

Specs on your motor come from manual 3
HP 188
WOT 4400-4800 rpm
Plugs AC-R42TS or Champ RV9YC
Gap .035
Timing 8 BTDC
Points .022
Dwell 28-34 degrees
Compression 150 psi
Fuel pressure at 1000 rpm 5 - 6.5 psi
Idle 650 - 700 rpm in gear

Suggest 19 pitch 3 blades

 

[Scott Danforth]

Also weigh your boat and compare to specs. You may be hauling aroud 1000# of water

 

[cajun1957a]

Hey thanks guys. I do like the five blade and the four blade works good too. I don't have a 19 three blade though.

Randy

 

[alldodge]

Good luck