Volvo 270 Gear Ratio

[Leon Phelps]

Hello,<br /><br />Have a Volvo 270 outdrive. It is on a Bayliner 2550 Sierra with a 10'6" beam. I have bought a spare outdrive for the boat. The spare outdrive has a gear ration of 2 1/4 to 1. <br /><br />My regular outdrive gives me 26mph at 3400 rpm. <br /><br />Does anyone know what the ratio should be for the best performance of the boat? I know that there are different ratios for the 270, but am unsure if I should have this one re-geared to a different ratio. I would like to not have to take my outdrive off to see what ratio I am using.<br /><br />Thanks in advance

 

[mercrewser]

Re: Volvo 270 Gear Ratio

I dunno but are you in snug harbor or three seasons? Welcome, its good to see a local guy on Iboats.

 

[Peter J Fraser]

Re: Volvo 270 Gear Ratio

The ratios are only dependant on the engine in front.<br />A V8 has a higher ratio than a 4 or 6 cyl. You would need to match what you already have in the boat.<br /><br />Cheers<br /><br />Peter

 

[Walt T]

Re: Volvo 270 Gear Ratio

I would think a 1.95:1 would be about right. Possibly in the 1.80's at sea level.<br /><br />If you have no current tag on the outdrive with the ratio on it, then using the prop pitch, engine rpms and speed you can calculate gear ratio. Use gps speed if possible.

 

[f_inscreenname]

Re: Volvo 270 Gear Ratio

D W <br /> From a not so great math wizz how do you do that?

 

[Walt T]

Re: Volvo 270 Gear Ratio

RPM / drive ratio X prop pitch /12 X 60 /5280= MPH<br /><br />If we know mph, pitch, and speed we can figure gear ratio thus:<br /><br /> Engine rpm<br />---------------------------- = Gear ratio<br />MPH X 5280 / 60 X 12 / pitch <br /><br />The problem with these formulas is they dont take into account prop slippage which is usually 10%