Question on different drive ratios 4cy VS V8?????

[TurboM700]

My curious mind has gotten me once again into a spot that I can?t figure out what?s the best way to go.

I currently have a Mercruiser 140hp in a Pontoon I built. On a good day she will run around 26mph. In the quest to make my wife angry I dragged home another boat with a 350 SBC Mercruiser in it. The boat was scrap but the motor and out drive are good. The outdrive is a 1:50:1 vs the 4cyl 1.98:1.

Knowing that the only difference in the drives is the gear ratio, strength is the same.

Is it better to spin a prop fast or slower?

This morning I built a Excel spread sheet where I can enter RPM,Prop Pitch, Gear Ratio, and slip and it will give me MPH.
This is what I got. So is it better to run a 19p faster to achieve the same MPH as running a 25p slower? I will leave my thoughts for now.

 

[craze1cars]

Re: Question on different drive ratios 4cy VS V8?????

Theory discussed heavily here. Probably never resolved:
http://forums.iboats.com/prop-questions-topics/prop-pitch-vs-gear-ratio-226406.html

If your drives are both interchangeable, you are in the unique position to test them both and pick the best of the 2 for your application. 6 bolts changes the drive real quick if going Alpha to Alpha of same generation. Not sure what exactly you have there...

Best of luck in your quest to anger the wife. Somehow that doesn't seem like an out-of-reach goal...

 

[TurboM700]

Re: Question on different drive ratios 4cy VS V8?????

Both drives are Pre-Alpha or Mc-1. You are correct on the easy change out. Props are a different battle as they are not cheap and it seems when you get higher up in the Pitch you get more into speed props then power props.

Thanks for the link I will read it tonight.

Mike

 

[Bondo]

Re: Question on different drive ratios 4cy VS V8?????

Both drives are Pre-Alpha or Mc-1. You are correct on the easy change out. Props are a different battle as they are not cheap and it seems when you get higher up in the Pitch you get more into speed props then power props.

Thanks for the link I will read it tonight.

Mike

Ayuh,.... Generally speakin' the range of standard pitch props runs from 15" to 23",....

You have to swap the gear ratio, so the motor will achieve it's designed Wot, usin' the pitches available,...

I can tell ya right now, you Can't buy a prop Small enough to run a 1.50:1 on a 3.0l motor,....
'n ya Can't buy a prop Big enough to run a 1.98:1 on a V8,...

Been there, tried that,...