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1990 Alpha gear ratio

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ArtK

Contributing Member
How can I figure out the upper gear ratio? I have read the lower ratio is 1.47:1.
The only # I can find so far is near the oil vent hole, it is OD463386, but I can not find any reference to that #.
Thanks in advance.
 
What engine? Length of boat?

The ratio is just left of the serial number.
If not visable use a pencil and rub as the ratio number is also stamped into casting under the decal where it should be visable.

The overall ratio may be 1.47:1 NOT the lower.
 
ratio is base on motor ans boat length the 3.7 and 4.3 motors use the 1.68 the 3.0 uses the 1.98. 5.0 and 5/7 use 1.49/1.50
what motor do you have?
 
There are only a couple online websites that will offer to show the gear ratio or engine details while searching the specific serial number in question.

That mentioned, while more challenging to decipher in especially in some cases vs others, this site Marine Engine.com offers a portion of details hidden within the model number that comes up when searching the/a serial number…

In this case serial number 0D463386 belongs to model number 5010198CS.

5010198CS the 198 would be the gear Ratio we’re looking for at least when the item in question left the factory… Had the ratio been changed for say higher altitude, then hopefully the service shop/tech followed the recommendations to scribe in the new ratio somewhere on the drive until.
 
ArtK said:
How can I figure out the upper gear ratio? I have read the lower ratio is 1.47:1.
The only # I can find so far is near the oil vent hole, it is OD463386, but I can not find any reference to that #.
Thanks in advance.
Click to expand...
Ayuh,..... I believe you'll find that the MC-1s, 'n Alpha 1s are 1.65:1 lower unit gear ratio,.....
When combined with the uppers, the final gear ratios can be 1.98:1, 1.84:1, 1.65:1, or 1.47:1 final ratios,....
There was also a 1.32:1 ratio used with the ole MC-1/ 351 Fords, 'n for the short lived BBCs MC-1/ Alpha 1s,.....
 
SO,,, my final ratio is 1.98:1 so the prop shaft is turning about half the rpm of the the engine,
and the lower gear ratio is 1.65 : 1, correct?
That makes a 3,000 engine RPM, using 1.98:1, 1515 prop RMP, 3000/1.98=1515 and that would be a drive shaft RPM of 2500 using the 20-24 (1.2:1 ) upper gear set. and 2500/1.65=1515 prop RPM
Am I correct? If so I Thank All of you for your input. ArtK
 
What is it you are trying to figure out?

Engine = 1 revolution

Prop = 1.98 revolutions if your drive is a 1.98:1 final ratio.

The vast majority of Alpha lower units are the same ratio (same pinion and driven gear tooth count)
There are exceptions but for this conversation based on a lack of your specific info we will go with that I said above.

Many outdrive service manuals will give you the upper and lower gear case gear tooth count to specifically determine upper ratio.


Again, what is your point?
 
here are the gear ratio breakdown. Not included is High elevation

MR and R drives
Lower Gears Pinion 17/ Forward 28
Final Gear Ratio/Upper gear case Tooth Count (Drive Gear/Driven Gear)
1.32:1 22/16
1.50:1 20/20
1.65:1 24/24
1.84:1 17/19
1.98:1 20/24

MR and R drives
Lower Gears Pinion 13/ Forward 21
Final Gear Ratio/Upper gear case Tooth Count (Drive Gear/Driven Gear)
1.29:1 20/16
1.47:1 22/20
1.62:1 24/24
1.81:1 17/19
1.94:1 20/24

Alpha 1 and Alpha 1 SS
Lower Gears Pinion 17/ Forward 28
Final Gear Ratio/Upper gear case Tooth Count (Drive Gear/Driven Gear)
1.32:1 22/16
1.50:1 20/20
1.65:1 24/24
1.84:1 17/19
1.98:1 20/24

Alpha 1 and Alpha 1 SS
Lower Gears Pinion 13/ Forward 21
Final Gear Ratio/Upper gear case Tooth Count (Drive Gear/Driven Gear)
1.32:1 20/16
1.50:1 22/20
1.65:1 24/24
1.84:1 17/19
1.98:1 20/24
 
kghost said:
What is it you are trying to figure out?

Engine = 1 revolution

Prop = 1.98 revolutions if your drive is a 1.98:1 final ratio.

The vast majority of Alpha lower units are the same ratio (same pinion and driven gear tooth count)
There are exceptions but for this conversation based on a lack of your specific info we will go with that I said above.

Many outdrive service manuals will give you the upper and lower gear case gear tooth count to specifically determine upper ratio.


Again, what is your point?
Click to expand...
So, you are saying the prop is turning almost 2x the engine RPM Not trying to make a point just trying to know how fast the prop turns. I didn't think that at cruising at 3300 rpm the prop would be spinning at 6534 rpm.
 
The gearbox ratio refers to the ratio between input and output revolutions. For example, a gearbox ratio of 2.51:1 means that for every 2.51 input revolutions from the engine, there will be 1 output revolution to the propeller.
 
kghost said:
What is it you are trying to figure out?

Engine = 1 revolution

Prop = 1.98 revolutions if your drive is a 1.98:1 final ratio.

The vast majority of Alpha lower units are the same ratio (same pinion and driven gear tooth count)
There are exceptions but for this conversation based on a lack of your specific info we will go with that I said above.

Many outdrive service manuals will give you the upper and lower gear case gear tooth count to specifically determine upper ratio.


Again, what is your point?
Click to expand...
Sorry , but 1.98:1 is Engine = 1.98 revolutions Prop = 1 revolutions
 
kghost said:
Ok you are the expert....
Think what you want....

You wont get any further responses from me.
Click to expand...
I'm far from an expert, but the help line people at Mercury are. If you don't believe me give them a call. sorry your feathers got ruffled.
 
OK SMART ASS,

SPIN ENGINE ONE REVOLUTION AND COUNT THE REVOLUTIONS OF THE PROP AND REPORT BACK WITH YOUR RESULTS.

WE WILL SEE WHO IS THE EXPERT!

Merc tech may or may not be experts but if the wording of your question was not exact, you got the answer you wanted.
 
No way is that prop going to spin at 5940 rpm with the engine at 3000 rpm. 5940 with a 17" prop would give you 95 miles per hour
 
Yeah drive is gear reduction i belive so with a 1.98 ratio engine will spin 2 x what prop spins. Larger higher hp engines use less gear reduction
 
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