Can anyone tell me if there is any marked differences between automotive engines and marine engines, specifically GM 4.3 V6's. Will it work if I take an engine from a Chevy S-10 pickup and put in place of my now dead 4.3 V6? Everything looks as though it will bolt up. Of course I will change out the water pump and address other incidential systems accordingly. Basically saying the short block will work or not? Will the operating RPM's make a difference? Automotive typically runs around 1800/2200 for highway speeds. Cruising speeds are usually 2x that.........hhhuuuuuummmmmm? Thanks for any and all input in advance.
Depends on the Year of the motor, the early model 4.3 block componants were different than the new one's, such as the counter balance shaft that runs off the cam gear, and the newer one's need an electric fuel pump, there ain't no hole for the pump drive. As far as the pistons and cam, thats where ya find the difference, the newer models do cruise at a lower rpm, but thats not where the torque is a torking. The marine type cam is designed to develope more torque at a lower rpm than the automotive cam, ya need that to get the boat on top of the water, the marine cam torque is peaked about 4200 / 4400 rpm, and the automotive cam is peaked around 5000 rpm. The pistons on a marine motor generally has flat tops with valve reliefs casted into them and most of the automotive pistons have a dish in the top of the piston relieving the compression and reducing hp.
Will an automotive motor bolt up and work for ya ? Yes ! but it will require a smaller pitch prop to perform at a slower speed, but once it's on top of the water and wrapped out it will do ok ... kinda
Sooooo, yes but no. It appears from what ya sayin' that this could be considered a failure to communicate even at its best outcome......... Better to just rebuild the merc engine with the right parts, put the darn thing back in the water and not look back........OK then! Got it!
Oh, one more question????? Anyone have any suggestions how best to booast the performance on our Mark Twain 140, 16' Demon (wanna be) go fast little boat. I'm taking out the 120 and putting in a 140 unless anyone has some suggestions on how better to pump up the 120. Considered re-fitting the little critter with a small block Chevy and a Berkley-Jet Drive. Just to make onlookers at the marina ask the obivous question,,,,,,,, WHY??? lolzzzzzzzzz
If it ain't wet, it ain't right!! 
