Gear Ratio ?

[Hondo65]

I have a Mercruiser 260 Alpha 1 Sterndrive. S/N 0B643994. The decal with the gear ratio was painted over and ruined. Anyplace else I can find the gear ratio? It has a 14.5"x17" prop.

Thanks

Hondo

 

[Haut Medoc]

Re: Gear Ratio ?

1.50 :1 ......​

 

[Hondo65]

Re: Gear Ratio ?

Thank you sir...

 

[Bt Doctur]

Re: Gear Ratio ?

1.50 if your positive it came from a v8, otherwise the upper needs to have the gear teeth counted.

 

[John_S]

Re: Gear Ratio ?

or just carefully (coil grounded) turn the engine over 1 1/2 times, in gear, and the prop should make only one revolution.

Pitch (17) seems on the low side for 350 in a 19' boat. Is this a heavy boat? What is the wot rpms and speed?

 

[Hondo65]

Re: Gear Ratio ?

I believe the weight of the boat to be about 2750 lbs. I just got the boat and have not run it in the water yet so no WOT or Top Speed. Typical load on the boat would be 400-800 lbs plus 30 gallons of fuel

Hondo

 

[Don S]

Re: Gear Ratio ?

Under the decal, it's stamped with the ratio, but with an 87, that means nothing if someone change the gears in a different upper housing.
I would suggest you run it and find out what your WOT rpm is.
Don't try to fix something that isn't broken.

 

[Hondo65]

Re: Gear Ratio ?

I thought that might be the case Don but I could not see or feel it. Tomorrow I will clean it up some more and look harder. And thanks for that simple wisdom. Sometimes I tend to get ahead of myself when I get a new toy. I will wait to see how she runs before I get into pouring money into the hole. Then I will revist this issue when I have more definitive parameters to share.


Thanks again

Hondo

 

[Bt Doctur]

Re: Gear Ratio ?

a 30gal. tank for a V8? typical flow with a 4bbl is 15-32gal/hr

 

[Hondo65]

Re: Gear Ratio ?

I figured it wouldn't be good but was wondering just how bad it would be. Maybe I'll swap it out for a paddle duct taped to a gerbil cage.

Hondo

 

[rad1026]

Re: Gear Ratio ?

Hey Hondo, I purchased a 1989 Chaparral 21' open bow three years ago with a V8 260. I bought it in dallas texas and the original gearing was 1.5:1. There was a 19 pitch prop on it. I run at altitudes of about 3500 to 6500 feet at the lakes around here. The best I could do with the 1.5 gearing was about 3300 RPM WOT. I wound up buying a new top end for the Alpha 1 outdrive with a lower gear ratio 1.62:1 I think. I have to go look at it again but I think that's it. With the 19 prop the boat flys. I've had it up over 50 mph at a lake over 4000 ft in altitude. I have dropped down to a 4 blade 17 prop though because for tubing and wakeboarding I can stay on plane at lower speeds and see the smiles on the kids faces. So altitude and what you use the boat for will also have something to do with your gearing and prop decisions. You have to run it and trim it out and see how she does. Let us know.

Also with this 21' boat at Lake Powell loaded with a full 32 gallon tank of fuel, 8 people, coolers the whole deal I have traveled up the lake 40 plus miles at about 3200 RPM on about 25 gallons just to give you an idea of fuel consumption.

 

[QC]

Re: Gear Ratio ?

You will get an average of around 3 MPG with that setup. Perfect for a day boat, don't stress about range, especially if you are running on lakes. Your 260 with a 20 footer ought to pull a 19" pitch just fine unless you are at high altitude as rad1026 pointed out. As DonS suggested, get some data and then start thinking. Nothing to think about yet . . .

BTW, rad1026, if your numbers are right your fuel economy sucks

 

[rad1026]

Re: Gear Ratio ?

QC how far is it from Lone Rock Beach to Dangling Rope up through the Narrows? I thought with that kind of weight I was doing good. I definitely need to do plugs, rotor and cap this year.

 

[QC]

Re: Gear Ratio ?

rad1026,

Yeah, looks like 40 miles to me too . . . There are not ANY 19 - 23 footers that I know of that do not get better than 3 MPG at cruise. Many break 4 . . . these are typically fuel injected, but your carbed 260 in a 21 footer should easily make 3. This assumes you are cruising in the 3000 - 4000 RPM range. Almost guaranteed, no way you don't get at least 2 MPG even super-duper loaded up. My bet is that you do get 3 and there was some other factor you missed.

 

[Hondo65]

Re: Gear Ratio ?

Well there may be a new fly in the ointment because the serial number on the sterndrive did not match the S/N on the Sterndrive tag that is on the engine. (The engine has 3 tags on it for engine, transom assembly and drive) Also where the gear ratio is supposed to be is the number 95. Any thoughts on that?

Thanks

Hondo