Quote:
Originally Posted by THEFERMANATOR
The engine you describe sounds like a 60 degree looper OMC which is like Spare said an optical ignition system engine. VERY good engines, and easily argueably the best engine OMC EVER turned out. They are also one TOUGH SOB. As for the extension on your MERC driveshaft, this is pretty unadviseable even from BAY who makes the adapter kits. It is ALWAYS best to go with a 25" lower unit with the spacer kit.
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Do you know what the normal compression is on one of those engines? The dealer told me that this engine has 80-85 psi on all cylinders. I know that my 91 has 93-95 on all cylinders, but 80 sounds a bit low?
As to the Merc, I have no doubt as to the accuracy of your statement that it's advisable to go with a 25" lower unit with a spacer kit, but the engineer in me has to know why. Aren't the gears and such identical in the 20 and 25's, the only difference in them being the length of the drive shaft? What is it I'm missing? 
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1987 V20 w/1987 150HP Yamaha on a Shoreland'r Trailer
1978 16.5 Airslot w/1996 120HP Force on a Four Winns trailer
1996 V21 w/1993 200HP Mercury on a Shoreline Trailer
All towed by a 5.7L Hemi Durango.
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