Engine Know-how: Cylinders, Torque, And Pistons

by Joe Guntherson

Everyone knows that if you want to pack a punch, the 8-cylinder engine is the way to go. You know it, I know it, the car dealer knows it, and if you check with your insurance agent to see if your premiums will increase when you trade in that 4- for an 8-, you can be sure he/she knows it too. But it's not quite that simple. Which engines really do perform the best? Well, to answer that, we need to look at a few engine basics.

In an engine, pistons (which thrust the fuel into forward motion so to speak) travel down cylinder sleeves allowing valves in the engine to open. These valves are called "intake valves" because once in the open position, they let fuel and air enter the cylinders. When the pistons rise, the amount of space inside the cylinder decreases, causing the fuel and air to compress. As we all know, compressed gases are more flammable. A spark, thanks to the spark plug, ignites the gases in the cylinder causing explosions that send the pistons back down. What goes down, must come back up, right? So when the pistons push back up the second time, a different valve opens -- the exhaust valve -- which pushes the combusted fuel/air mixture out of the chamber. The pistons in an engine come in even numbers (hence, the 4-cylinder, 6-cylinder, and 8-cylinder options). The reason for this is because for every piston that's up, there's a partnering piston that's down. These pistons are connected to rocker arms that turn the crankshaft, which causes the wheels to turn. The constant switching of up-and-down pistons (two up while the other two are down in a 4-cylinder engine) is what causes fluid, forward motion of the vehicle.

Once we understand the function of the pistons, it's easy to see how a 6-cylinder engine produces more power than a 4-cylinder engine. Two extra cylinders, two extra pistons. More fuel being burned with each turn of the crankshaft, more money spent on replacing the amount of fuel you burn.

For the most part, 4-cylinder engines provide adequate power for small, light cars. However, the 6-cylinder engines are more responsive and fairly standard on small trucks, mid-size cars, and SUVs. Larger, heavier SUVs and larger trucks, designed for towing or hauling, often feature the 8-cylinder engine. But is bigger always better?

This is where 'torque' comes into play. Take for example, the Isuzu Ascender, the popular five-passenger SUV. Designed to be able to haul your whole family, plus tow those wave runners you bought with last year's Christmas bonus, the Ascender only features a 6-cylinder engine. Why not eight? The answer: torque. The design of the Ascender's 4.2-liter Inline 6-cylinder engine actually generates 285 horsepower and 276 lbs.-foot of torque -- more power than some 8-cylinder engines.

Torque and horsepower are significantly more complicated than simply understanding how pistons and cylinders affect power. But the basic principle is that every car's drive train (the system that converts the fuel to power and the method of getting that power to the vehicle's wheels) is slightly different, and some are more efficient than others. So a 6-cylinder engine which operates more efficiently can, in reality, provide more horsepower while burning less fuel than an 8-cylinder engine with a less stellar design.

About the Author

Test drive the new 2008 isuzu trucks at a local dealer. You can also do a suv comparison to see how the Isuzu line of trucks and SUV's lead the competition!

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