"John, the 1992 150 Merc's
"John, the 1992 150 Merc's came in two different versions - one had a 2 liter block (shared with the 135 horse) and the second had a 2.5 liter block (shared with the 175/200/225's).
I believe the smaller block was simply called a 150 Black Max and the larger would have been an XRI, XR6 or Super Magnum model.
Factory spec on compression is stated as "110-135 psi with variance not exceeding 15 psi between cylinders cranking with a fully charged battery, throttle shutters wide open and cylinder block warm" (almost verbatum from Merc)
These engines have lot's of power and should be more than enough on an 18 footer.
Just on a personal note/preference, I don't like motors that produce more horsepower than they have cubic inches of displacement. Anytime the ratio is less than 1:1 you are putting excess stress on the motor - which in my opinion is why you see so many high horsepower motors that have been rebuilt within 5-6 years of age.
The 2 liter (121.9 cu in) models are probably better suited to 135 horses. That still leaves it below the 1:1 ratio (at 0.9:1) but alot closer than in the 150 version (0.81:1) - so in my opinion a 150 with the 2.5 liter block (153 cu in) with a ratio of 1.02:1 would be the more durable engine during it's lifetime.... (just my opinion)
As to running in salt - definately takes years off the motor - more so if it wasn't flushed after each use. Also tends to seize all sorts of hardware making work on these quite difficult.
I restored a 3 year old motor that had hung off the back of a boat in saltwater year round. I had to totally disassmeble the motor and broke every single fastner in the process, including snapped bolts on the powerhead that require drilling/tapping - so give it a really good look over, if it doesn't look like it has be super-cared for I may tend to back away from it unless the price really reflects that.
As a last note, a 1992 150, regardless of the particular model would normally sell for somewhere between 1000-1500 bucks in the used market if it is running well and has been properly maintained and checked out prior to sale..."
