High Altitude Gear Ratio? 5.7L OMC

[bullsnot]

Hey guys I've got an 88 2450 Ciera in fantastic shape with a perfectly working time bomb draggin in the water off the back, for now that is. To counter this I'm looking at doing an OMC to an Alpha 1 Gen 2 conversion but the problem is I'm not sure what gear ratio to put in the new drive.

Currently I have a 5.7L OMC drive with high a altitude gear ratio. (Stamped on a tag on the side as high altitude gear ratio) Since the altitude I boat is anywhere from 4500 to 7000 ft I'd like to stay as close as possible to the current ratio since it seems to be about right.

Where the heck can I find what gear ratio I have? I'm assuming I'd continue to use the same props right? Anything else I've failed to consider?

Thanks in advance.

 

[treeeman00]

Re: High Altitude Gear Ratio? 5.7L OMC

drain the oil from the outdrive and pull off the top cover that has the dipstick (4 bolts). Top gear should be 21 teeth and bottom gear should be 16. That's the most accurate way I have found.

 

[jerryjerry05]

Re: High Altitude Gear Ratio? 5.7L OMC

IF???? Your drive is stock or original.No ones changed it or replaced it?
You should have a 21.16 upper and a 14.26 lower.
Mercruiser used a 1.5-1 ratio on all the mid range v-8s
And 1.32-1 for big blocks(hope memory's right).
On the drive under the port side trim ram there "might" be a tag.
Post the info on that tag.

 

[bullsnot]

Re: High Altitude Gear Ratio? 5.7L OMC

I should've looked harder, I'm somewhat embarrased but the tag on the drive has the gear ratio. It is 1.59:1

Thanks for the responses guys.