Horsepower Mods.

[greenman407]

After you have been running boats for a while your thoughts will naturally turn to going faster and producing more power.Its only human, trying to better ourselves and our projects. I just love the word retrofit. Has a nice ring to it. At first we will concentrate on increasing the density of our fuel charge(packing more fuel into each cycle of combustion).Since most if not all glow engines are 2 cycle then the piston and sleeve is where we will focus first since they are the heart of the matter. The piston and sleeve serve as the makers of compression and the valving of the fuel charge. You can see here the piston and sleeve. The ports location up and down and shape determine timing and density of charge. Where the pointer is you can take your dremel or other such tool and heavily chamfer this edge up to a knife point. The fuel, on its way up to the ports to be admited to the cylinder, is squeezed between the walls of the case and the walls of the sleeve. At 25,000 RPMs it has only milliseconds to reach its destination. It only stands to reason that the easier it is for the fuel to get there the more will have time to get in before the door is shut so to speak.

[greenman407]

Continuing on to the other ports. By the way, this operation is called(you guessed it) porting. The pointer is pointing at the exhaust port. The higher the port is the more advanced your timing will be. The lower it is the more retarded it will become. You can remove the center partition and cut into the upper side of the port with a cutting bit but only take off a little at a time because it makes a big difference, becoming unreliable if too much is removed. Since there is a wide variety of engines I can not say exactly how much to take off, it is a matter of experimentation. Start with 15 thousands and see what you get.

[greenman407]

Notice the port on the right side. See how it is angled downward at a 60 or 70 degree angle. You need to do the same with the other two intake ports.When the piston comes down it effectively blocks off the flow of fuel upwards, so by taking material off the bottom skirt of the piston directly bellow the intake ports you allow extra fuel to squeeze past. I have seen a radius cut made in pistons to as much as 65 thousandth or 1/16". Here again you need to sneak up on it a little at a time or you wont be satisfied with the results.

[greenman407]

The crankshaft of an outboard engine is hollow to allow a pathway for the fuel to get from the carburater to the crankcase before its final push up to the cylinder. heavily chamfer and round out this area indicated by the pointer. Dont take off too much as you will reduce the weight of the crankshafts counterweight and throw the engine out of balance. This is the opening in the crankshaft that the carburater feeds directly into. It is right under the flywheel. Chamfer and somewhat enlarge these areas as well.

[greenman407]

This is an exhaust throttle for an inboard engine, you can see it here installed. Its amazing how it works. In a engine that has a carburater the intake stays closed by virtue of the carburater barrel, with just a slight opening to admit air at low speed to maintain a strong vacuum. With the exhaust throttle and its accompanying ventura the intake is completely open all the time ,even at Idle(if you can get it to idle). But the exhaust throttle that is mounted on the exhaust(hence its name) is the one that stays closed(throttling the engine). It regulates what is allowed to come through the engine. The advantage is faster throttle response and power. The downside to it is a very fast running engine, one that will need more maintenance. For those that think this hobby is too loud we have these: If you are ready to put a tuned pipe on your outboard you will need one of these: A tuned pipe header.