Most folks understand why a two stroke engine offers so much more power than a comparably sized four stroke engine, the “secret” being that the two stroke pistons get forced down by a burning charge of air and fuel every single time as opposed to every other time in a four stroke. This enables a higher horse power to weight ratio and as a result the two stroke engine can be lighter than a four stroke of comparable power. Another benefit is the abundance of power that is available at lower engine speeds vs. a four stroke. Having all of the pistons on a power stroke each and every time clearly gives the advantage to the two strokes.
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.