This is a fairly common question. The truth is that the marine engines are in fact different than the automotive variety. The “marine” engines came from the Tonawanda facility but now come from Toluca MX. The cam is different, the valve guides are different, valve seats, bore tolerancing, etc. In my experience you can use an automotive engine in a marine appication and make it functional however there are some differences and the product just won’t last as long. The best example I can give you in thinking about why is how often do you run your car engine for extended periods of time at 3,500 – 4,000 rpm which is very common for a marine engine. The “Duty Cycle” requirements for a marine engine are different than automotive and therefore to make it last like it is supposed to this operating criteria is taken into account. Therefore the casting level of the block may be the same p/n however they machined the bore with greater tolerance ranges for this purpose on certain applications, made adjustments to the valve seats for extended running at laoded conditions, etc. Here’s a link to more technical information.

http://tinyurl.com/3xvru29

http://tinyurl.com/y93z2gc