You might think that your Volvo Penta powered boat has a Volvo engine in it and your Mercruiser powered boat has a Mercury engine. While the engines have been modified extensively for marine use, in almost every case, they are engines built by General Motors Corporation. Yes, the car company.

Over the past 50 years or so, many companies have built stern drive engines including Mercury Marine, manufacturer of Mercury Outboards and Outboard Marine Corporation, whose stern drive products evolved into some of the current Volvo Penta line. OMC modified outboard motors to run mounted on their sides and power stern drives back in the 60’s. Merc built a 3.7 liter engine using their own aluminum engine block and a few Ford components. All of these have fallen by the wayside today and we see GMC engines pretty much across the board in current production.

So what is different between the engine in a Chevy Tahoe and the one in a boat? There are several things. The engine block “freeze” plugs, for example. These are not really plugs to allow for freezing but are plugs that cork up holes left in the outside of the block during the manufacturing process. These plugs are usually steel on car engines because the block is filled with anti freeze which inhibits any corrosion. In stern drive engines, these plugs are changed to brass because most boats run raw water through the block. Raw water is pulled into the engine from the lake, ocean or river and after a pass though the cooling system is blended with the hot exhaust at the back of the manifolds and discharged. Steel plugs would rust out quickly so brass is used.

Because there is no downhill coasting in a boat, the engine is under load constantly while underway and because there are no gears other than forward and reverse, a boat engine’s torque characteristics must be different from automotive engine. This change is accomplished a number of ways but the most significant variance from automotive is in the camshaft. Ignition and fuel injection tuning is also calibrated to adapt the engine’s performance to the marine environment.

All components of the engine mounted fuel system have to endure a burn test where the engine is placed on what could best be described as an industrial barbeque and is set afire. No component of the fuel system can leak for a specified amount of time while it is on fire.

The electrical system has to be modified to prevent any sparks that would normally be generated by electric motor brushes, alternator brushes, relay contacts, and the like. This prevents them from igniting any fumes that may accumulate in the engine bay.

The exhaust system is fully water jacketed to isolate the red hot exhaust from the engine box area. Water is blended into the exhaust just before it enters the stern drive’s exhaust passages to cool it to manageable levels.

A specially designed bell housing adapts the rear of the engine to its mounting place in the boat.

There are many similarities and many components are exactly the same but there is also much dissimilarity. Many components that appear outwardly to be the same are in fact significantly modified for marine use and should never be interchanged.

The Wiz

Two strokes have traditionally been somewhat wasteful of their fuel. The very design required that some of the intake fuel and air charge be lost on every single stroke. E-TEC engines completely solved that problem. The E-TEC injector provided the cure that turned the very dirtiest engine design into the very cleanest.

I am often asked what it is that makes an E-TEC so special. What makes it run so much more cleanly than a conventional carbureted two stroke engine?

Conventional two stroke outboards run the fuel/oil and air mix (called “charge”) through the crankcase and use the pressure created in the crankcase by the descending piston to force the fuel up on top of the piston. Lots of oil is mixed in because the oil is constantly washed away by the fuel in the charge. The overdose of oil ensures that some stays behind to lubricate the moving parts.

1) The piston rises and sucks the charge into the crankcase through the one way valves called reed valves.
2) The piston descends and the reed valves snap shut. The charge compresses within the crankcase.
3) The piston continues to descend and passes the exhaust ports. With these ports open, the burnt gases (exhaust) from the firing that previously occurred start to pass out through them.

4) The piston continues to descend and passes the transfer ports. These ports run from the crankcase where the compressed charge is, to the cylinder above the piston. The charge starts to rush in to the combustion chamber. The charge, which is entering through the transfer ports now fills the cylinder and finishes pushing the exhaust out. Some of the charge leaves with the exhaust. The result is unburned fuel and oil is dumped with the exhaust. This results in smoke and wasted fuel.

E-TEC’s run plain air through the crankcase. No fuel, no oil. Oil is injected into different areas of the engine in tiny amounts. The oil is not washed away like it is in conventional two strokes because there is no fuel in the charge to do this.

When the transfer ports open, plain air enters the cylinder. It pushes the old exhaust out in the same way, but contains no oil or fuel, so none is lost. The piston gets all the way to the bottom and comes back up to the point that the exhaust and transfer ports are closed. It is now that the fuel injector fires the fuel into the cylinder. The E-TEC injector’s unique abilities shine here. They can generate hundreds of pounds of pressure internally and get the fuel to enter and properly atomize in the compressed air within the cylinder. With no path out, all fuel is contained and combusted.

Oil consumption comes primarily from the residue of oil that is left on the cylinder walls during combustion. This is an amount that is similar to what is left on the cylinder walls of your car’s engine. You don’t go through much oil in your car and you won’t with the E-TEC for the same reason.

On top of all of this, the oil that is consumed is completely combusted and the resultant exhaust meets or exceeds the strictest environmental standards.

Does this all sound too good to be true? Well it is both “too good” and also true.

E-TEC will have this edge so long as their patents hold out. When they expire, everyone will be doing it this way.

The Wiz