Re: Est. HP of a older Merc Tower of Power
While it is true that "There 'aint no substitute for cubic inches"--Even though it is a six cylinder engine, it is a small bore and a .030 overbore will only yeild 2 maybe 3 or 4 cubic inch increase. And about 1/3 of that displacement is in port area so is relatively useless. For example, on a 100 cubic inch engine 4 cubic inches would only be 2-3% increase. But, even if you acheived a 4% hp increase, that still only works out to about 5 HP. Since the most important consideration --given a narrow range of cubic inches-- in increasing horsepower is port timing, your engine will not see much horsepower gain from the overbore. --Maybe a couple of horsepower. So: if your engine was ported to produce somewhere around 115 HP, then simply overboring will not increase output by very much. Other modifications would need to be made along with the increased cubic inch displacement.
However, in the past, it was commonly known that Mercury understated the horsepower of its engines--especially the smaller ones. That's why it was so difficult for competitors to keep up with them.
If they continued that practice to the newer powerhead then indeed you are producing more than 115 horsepower. But how much more? who knows?
And, remember, since it takes exponential increases in HP to gain linear increases in speed, 10 horsepower is only going to yeild 1-2 MPH more on the same hull
So don't expect that you have a magical engine with 130-140 horsepower.
