Re: gear ratio differences
Per my sales brochures, over the years Merc/Mariner ran 3 ratio's and 2 gearbox diameters on the 150 including the XR/Magnum series. I can't tell you exactly which is which.
They had 4 1/4" and 4 3/4" gearboxes and ran 2.0:1, 1.87:1, and 1.78:1 ratio's. I know in '94 Mariner had the smaller gearbox and 1.78 ratio. I can't prove or disprove if Merc had that also or if it was unique to Mariner. By '97 merc was only offering the 2 or 1.87. They both originally had the 2 liter powerhead and later on the XR/Magnum had a 2.5 liter powerhead. Seems the larger powerhead had the l.87 gearbox.....but also had the 4 1/4 box, at least for awhile..... whether or not it was on the XR I don't know.....but you can measure it.
In short here are some options. With a ruler and counting turns per turn you may be able to get your answer. Sorry, this is the best I can do.
Mark
