Auto vs Marine

[Danny Bailey]

It's all a matter of torque load and rpm. If you prop a car engine to run at the same torque output as it experiences in a car, and run it at the rpm's it sees in a car, it will last. Problem is nobody does that. They want to take an engine designed for say a continuous output torque of 120 ft lbs at 2200 rpm, stick it in a boat, and run it at 250 ft lbs and 4000 rpm. It just will not stay together. I have seen some big cube gas engines that have held up, but they were built for boats with heavy duty pistons, bearings, 'truck' grind cam, etc. My Cummins are designed and built to run at 600+ ft lbs and 2500 rpms, and they will do it for thousands of hours because this is what they were made for.

[Paul]

I'm a GM engine fan and have been all of my life. I know these engines fairly well so the following will be based on GM / Mercruiser.

Lets take the 305 for instance. Take one of these out of a Chev Montecarlo, put a marine carb, distributor & fuel pump on it (thinking it is now a marine engine) and stuff it in a boat. No I dont want to go for the maiden voyage and I hope your a member of Sea Tow. The peak torque curve and Hp are great for the street but useless in a boat.

Now take that same 2 bolt main block, crank and cylinder head casting and rebuild it with the appropriate marine cam profile, valves, HD pistons & bearings, windage tray along with a marine carb, distributor & fuel pump. What you'll end up with is a 228 Hp MerCruiser which is what my boat came with. Although this was a good engine, I chose to replace it with a 350 for increased torque.

Reliability in an engine is something that I dont' take lightly. I've been using the same engine builder for several years now and rely in their expertise. These guys build marine, automotive & industrial engines all day long and for me personaly have built several Drag Racing and marine
engines. They also agree that not all castings are the same however the distinction is not between marine/auto, its between standard and and hi performance.

The 350 that they built for my F-26 is built from a block and crank cast for a '69 vehicle such as a Chevelle SS and the heads were cast for a '70 vehicle such as a Camaro. Toss in a marine cam, Hi performance pistons & bearings etc and I now have a bullet proof engine with ample power to push my boat around the lake.

As far as aftermarket heads go, I know some people with aluminum Dart heads in their 90 mph Bajas and Formulas that that would argue that these heads are fine in a marine application.

Thats my 2 cents