Starting the cycle, the piston will head down the bore. Since the piston is accelerating at great speed, it will create a pressure drop within the cylinder as compared to the pressure in the intake manifold.
Racing Technology with Evan J. Smith How and Why Internal Combustion Works, Part 1 Illustrations by John McBride I t’s safe to say that most drag racers become addicted to the sport after hearing the roar of a high-power V-8 or after watching a wild hot rod launch with the wheels up. At some point, each of us got the chance to get behind the wheel (or the wrenches) — that’s when the real fun begins and the addiction grows. Drag racing is indeed addictive, and it doesn’t take long to yearn for more power, harder launches, and lower elapsed times. With the exception of a few electrically powered drag vehicles, our beloved acceleration relies on internal combustion to propel us downtrack. More power equals better acceleration and greater top speed, so we’re always on the hunt for those precious ponies. Most racers can rattle off a list of high-performance engine parts that will usually help achieve greater power figures, but there are plenty of people who do not understand exactly why these gains occur. We’ve all heard the engine is nothing more than an air pump, and this is partially true, but the exact function of internal combustion is a little more technical and complicated. In basic terms, the engine is a tool which are forced down the bores, mystery gas; instead, it provides what happens to fluids (remember, used to harness the energy released thusly transforming the up and down additional oxygen to the combustion air is a fluid) under changing from burning a precise mixture of motion of the pistons into a rotating process. Sticking with natural pressure conditions. hydrocarbons (in most cases gasoline) force at the crankshaft. The repetitive aspiration, we can increase the To understand what takes place and oxygen. A fuel source, such as cycle of cylinder after cylinder burning displacement of the engine, we can rev inside the engine, let’s look at typical gasoline or methanol, is mixed with fuel and oxygen creates a seamless it higher, we can (of course) add four-stroke engine operation. Starting oxygen (at the proper ratio by a flow of power and a nice rumble from aftermarket components to improve the cycle, the piston will head down the carburetor or EFI system) and is then the exhaust system. But how do we efficiency, and/or we can make the bore. Since the piston is accelerating at ingested into the engine, where it is increase the power? existing engine run more efficiently by great speed, it will create a pressure compressed and then ignited. The Over the years, we’ve learned a few reducing parasitic drag. drop within the cylinder as compared to rapid burning (not exploding) of the ways to increase power from the But this still doesn’t answer the the pressure in the intake manifold. So fuel/air mix expands in the cylinders beloved internal-combustion engine. question of just how oxygen and fuel when the intake valve opens, the air/fuel with a resultant release of heat energy We can do it unnaturally by using makes it to the cylinders. For this, mixture rushes in to fill the void and and force. The extreme force (cylinder some form of supercharging. We can we can thank Mother Nature and a equalize the pressure. We call this the pressure) is applied to the pistons, also use nitrous, which is not a few early scientists who figured out intake stroke. (Above left) During the intake stroke, the piston goes down the bore. This creates a pressure drop (Above left) Just before the pistons reach top dead center, the spark plug fires and in the cylinder (relative to the pressure in the intake) so when the intake valve opens, the air/fuel the mixture ignites. As the oxygen and fuel burn, energy is released, and the mixture rushes in. However, there are many factors that determine how much air and fuel make expanding gasses force the piston down the bore. It’s commonly known that higher it into the cylinders. (Above right) On the compression stroke, both valves are shut and the compression ratios produce higher cylinder pressure and greater power. (Above pistons compress the mixture into the combustion chambers. Naturally, more air and fuel right) Lastly, the piston will cross bottom dead center, the exhaust valve opens, and (actually oxygen and fuel) ingested means there is greater potential for horsepower to be made. the hot exhaust gasses are expelled on the exhaust stroke. 70 ✦ National DRAGSTER the cylinder of spent gasses but will also reduce the Member Track Special Programs Schedule workload (pumping energy) on the pistons, which frees The NHRA member tracks listed in the calendar below will be hosting a special event on up horsepower. the date listed. To schedule an event, track operators should call the NHRA Field Though our race engines Marketing office, 626-914-4761. For complete schedules, log on to NHRA.com. run without second thought, the power they create is not free; it actually costs power to make power. For instance, there are losses due to internal friction, like that found between the rings and July 18 July 18 July 18 the cylinder walls, and there Atlanta Dragw
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