To a lot of us, engines are a bit like women. We can usually figure out when something is wrong, but we don't know for sure what makes them tick. That's because engines, like the fairer sex, are complicated.
An engine is basically an air pump. The standard gasoline-powered internal-combustion engine, the sort of contraption that most likely is under the hood of your rig, uses a four-stroke combustion cycle to convert air and fuel, which is mixed at a ratio of about 14 to 1, into energy. The four-stroke cycle used by our engines sometimes is referred to as the Otto cycle, after Nikolaus Otto, who invented it in 1867. In the first stroke, known as the intake stroke, the piston starts at the top of the cylinder. As the piston moves downward, the intake valve opens and the resulting vacuum fills the cylinder with a fuel/air mixture. Next comes the compression stroke, where the piston moves back up the cylinder to compress the fuel/air mixture, which it can do because on this stroke, the intake and exhaust valves are closed. When the piston reaches the top of its stoke, the ignition system sends an electrical charge to the spark plug, which does its job and emits a spark, igniting the mixture. The resulting explosion drives the piston downward, thus turning the crank through the connecting rods and sending power to the transmission. This part of the cycle is referred to as the combustion stroke. The final part of the cycle is the exhaust stroke, in which the exhaust valve opens and the piston makes another upward stroke, as always driven in part by the rotational forces of the flywheel, to push the remnants of the ignited mixture out of the cylinder.
If you're like us, you're wondering how your engine works within the context of looking for more power from it. And this is where things start to get complicated. Besides just understanding the basics of how an engine works, you must also understand what horsepower and torque are. Horsepower is defined as a unit of power numerically equal to a rate of 33,000 lb-ft of work per minute. Torque, meanwhile, is the twisting motion that tends to produce torsion or rotational motion. Well, fine, but these definitions really don't apply to the real world, do they? So what are torque and horsepower when it comes to the real world? To put it simplistically, horsepower is the ability to move weight a given distance, while torque provides the ability to get that weight moving.
So is it better to have torque, or is it better to have horsepower? For the most part, the more you can have of both, the better. Lots of horsepower is great, but without low-end torque, horsepower, especially at the top of your engine's rpm range, is fairly useless-unless you are a professional mud racer or spend a lot of time in the dunes at high rpm. A ton of torque is also a good thing, but without appropriate horsepower, it's also of little use. For the most part, a healthy balance of both, with as much of the torque as possible in the low end of the rpm range, is the best setup for an all-purpose trail rig.
Now that you have a little clearer picture of how an engine works, and of what horsepower and torque are, the quest for more power can begin. Because an engine is an air pump, the majority of modifications you can make to improve its power output involve making the engine inhale and exhale more effectively and more efficiently. As more fuel and air enter the engine, and spent gases exit the engine more quickly, horsepower is unleashed. Let's take a look at the basics of what is inside of your engine and how those parts can produce more power.