What is the gear ratio for a 1971 mercury thunderbolt 650?

[dan2744]

Wondering what the gear ratio is for the 65 hp merc from 1971?

 

[racerone]

Why do you ask this question ?

 

[dan2744]

It's what ended up on my 1965 90 hp merc, marina said it was a 1966, it's a 1971. It's working, I just think I have lost top speed.

 

[clueless75]

Ratio is 2:1

 

[Faztbullet]

All 4 cylinder crossflow inlines are 2:3:1 ratio......

 

[racerone]

Ratio from the 1971 factory brochure is listed as 13:30-----But check it yourself.----Motor in forward.----Turn flywheel untill prop moves.---Mark position of prop.-----Turn flywheel 10 revolutions while counting revolutions of the prop.---Then do the math.

 

[clueless75]

In the appendix section of this manual (http://boatinfo.no/lib/mercury/manuals/mercury_1965-1989_40-115.html#/30), it says gear ratio is 2:1... Am I wrong?

 

[Faztbullet]

Ratio from the 1971 factory brochure is listed as 13:30

30 divided by 13 =2.3:1
Here is most popular ratios:
40 & 402 2 cylinder.......................................... ..2:1
40/45/50/500 4 cylinder......................................2:1
50/60/650/700 3 cylinder....................................1:64:1
650/75/80/800/850 4 cylinder..............................2:3:1
900/90/1150/115/1400/140/1500.........................2:1
1970-71 1150 & 1350.........................................1:78: 1

 

[dan2744]

Thanks guys, it seems to run okay, I can't get it over 32 mph but I can live with that.

 

[dan2744]

19 pitch prop.

 

[clueless75]

32mph is pretty good for 65hp!

 

[dan2744]

It's 90 hp powerhead, 65 hp lower unit

 

[clueless75]

Oh. I get about 31mph with my 1975 85hp merc with a 17p prop on my incredibly light boat, so 32 still isn't bad

 

[dan2744]

Thanks, I just wanted to know if thst was okay, boat is 935 lbs dry.