Alpha one gen 1 upper gear ratio question

[Jussi-T.]

Hi, I have a -89 Mercruiser 3.0 with alpha one. I am going to change the outdrive. The currently drive upper gears are: U-joint shaft 17, vertical 19. The new drive has: U-joint shaft 20, vertical 24. So i counted the upper gear ratios: 1,11765 and 1,2.
I am thinking, that this 1.11765 isn't the original gear ratio for this engine, maybe someone has changed the upper unit before(from V6 maybe?) but the 1,2 would be the correct gear ratio for this engine? Am I right?

 

[achris]

Re: Alpha one gen 1 upper gear ratio question

The ratio is quoted as the TOTAL ratio of the drive, not just the upper. That's because there are different ratios in the lowers too.

The correct ratio for a 3 litre is 1.98:1. That is a 20-24 in the upper and 17-28 in the lower.

17-19 is from a drive with an overall ratio of 1.84:1, and was used on earlier V6s (the later ones use 1.62:1) and '470's.

Chris.....

 

[Don S]

Re: Alpha one gen 1 upper gear ratio question

Here is the ratio information from the sticky at the top of this forum.

 

[Jussi-T.]

Re: Alpha one gen 1 upper gear ratio question

Ok, thanks! What do you think, is this swap from 1,84 to 1.98 going to affect to the top speed for how much? The boat is a 17 ft wellcraft classic (Br)

 

[Don S]

Re: Alpha one gen 1 upper gear ratio question

With the 20/24 gears, you will then have the proper ratio, and with the proper prop and WOT rpm, you will probably go a bit faster.