Frank Acampora
Supreme Mariner
- Joined
- Jan 19, 2007
- Messages
- 12,004
It does sound a little fishy but there is good sound engineering going on there: The old engines and the Chrysler engines from which they derived had equal compression on all cylinders. This was due to ease of manufacturing. When Brunswick and Mercury got their hands on them they started to make changes. Because the center cylinder has a smaller crankshaft counterweight, the crankcase is less "packed" resulting in slightly less fuel/air delivery to the combustion chamber, thus slightly less horsepower. Thus, higher compression on that cylinder to try and equalize horsepower to the top cylinder.
I'm not sure about the bottom cylinder but there is where the spit-back recirculation hose from the airbox enters the manifold. A similar situation may occur resulting in slightly less horsepower production on that cylinder which higher compression would help alleviate.
Thus the factory is trying to generate less stress on the crank and a true 30 horsepower at the prop from each cylinder.
I'm not sure about the bottom cylinder but there is where the spit-back recirculation hose from the airbox enters the manifold. A similar situation may occur resulting in slightly less horsepower production on that cylinder which higher compression would help alleviate.
Thus the factory is trying to generate less stress on the crank and a true 30 horsepower at the prop from each cylinder.