Re: WOT for 1971 Mercruiser 165 6 cyl
My book only goes to '74, but most outboard 6s are 5000-5800rpm. My 150 is the highest at 5300-5800, 140s and 115 lower, 5k-5.5k. A 150 XS is a little higher though. I would look for 5000+ minimum for a start until you see a manual. New v-6s are around 5000-5500. I have seen this done for fuel economy and such, hard to believe it really matters much as you are lugging the engine and making it run under loads it is not designed for.<br /><br />Unless you have an I/O and a car motor. Then you are maybe looking at around 4000 I would guess. Set the timing at full advance with an adjustable timing gun. I would guess 34 degrees if no detonation, or some say to crank the timing up until you go the fastest with no detonation; 'power timing'. You can overprop these for part throttle use due to the automotive engines great torque at the lower rpms at mid speeds. It will go faster at the right top rpm of course. You need to find out what it is first and make sure your tach is close too with either type of engine; that is key. <br /><br />Unless modified you will go the fastest at the top spec rpm with an empty boat 9 out of 10 times. ANY damage to the prop will slow you down. I round the leading edge of the prop blades with a hand file, maybe 5 min or less per blade is all it takes on aluminum. Take the least amount of material off, just get rid of the corners and make it sort of sharp. That's good for a free 1-2 mph.
