How to get more horsepower out of an engine?

Increase displacement
More displacement means more horsepower. The more you can burn gas during each revolution, the more you'll get power. You can increase displacement by making the cylinders bigger, lengthening the stroke, or by adding more cylinders. Hmmn.. Now how can I add more cylinders to my current engine?-)


Increase the compression ratio

Higher compression ratios produce more power. The more you compress the fuel/air mixture, the more power it makes when it explodes. If the gasoline's octane rating is not high enough, the fuel/air mixture will burst into flame before the spark plug even ignites. That is why racing cars normally require high octane gasoline


Rev the engine more

The faster the engine is running, the more power is makes. However, you can't just rev the engine infinitely because the intake- and exhaust pipes would become too small. Also all the moving and rotating parts must be up to the job and some parts as camshaft(s), valves and valves prings must be designed for high reving in order to get the extra ponies..

Many people assume that the ultimate rev limit of a engine is the strength of the crankshaft or the connecting rods.. wrong. Valve bounce is the number one killer of engines with high rpms. Do not overrev, the factory redline is there for a reason. Although the damage is normally caused when it's on the shift down-change, and the engine gets over revved.


Stuff more into each cylinder

If you can cram more air (and fuel) into a cylinder, you can get a lot more power!

There are few ways to cram air into the engine: turbocharger, supercharger, and nitrous oxide system. Turbochargers and superchargers pressurize the incoming air to effectively cram more air into a cylinder. With NOS one can basicly increases the oxygen level in the cylinder.


Cool the incoming air

Like everyone who's been awake during the physics classes knows, compressing air raises its temperature. But the engine produces more power when the incoming air is cool. This is because the hotter the air is, the less it will expand when combustion takes place. Therefore, many turbocharged and supercharged cars have an intercooler. Intercooler cools the compressed air before it enters the cylinder.

Always take the air for the engine from a cool spot. It is very usual to see engines with cone-airfilters just behind radiator, sucking air warmed by the radiator - bad idea. Making a cold air induction system is always a good idea, but make sure the opening is not located in warm place.


Let air come in more easily

By chancing the camshaft to a more aggressive type, it is possible to get more air in the engine. More aggressive camshaft basicly changes the valve opening and closing times, and lengthen the opening clearance. Air resistance can also be lessened dramatically by putting two intake valves in each cylinder (Like in 16v engines).

By making larger intake manifold, or by polishing the current one, you can eliminate air resistance in the intake system. High-flow or just bigger-than-stock air filters can also improve the intake system's capasity, but only if the filter is the narrow part in the system. When designing a cold air induction system, try to locate the opening in high pressure area with low temperature, such as the nose of the car.


Let exhaust exit more easily

If the exhaust is too small, or the mufflers have a lot of air resistance, it will rob some engine power. However, the exhaust shouldn't be too big either, or you will lose on the torque side. Air resistance can be lessened by adding a second exhaust valve to each cylinder (Like in 16v engines).

Always keep attention on small details, such as the location of exhaust pipe's end tip. Always locate it in low pressure area in order to let the exhaust gasses flow easier out from the pipe.


Make everything lighter

Lightweight parts help the engine perform better. Each time a piston changes direction, it uses up energy to stop the travel in one direction and start it in another. The lighter the piston, the less energy it takes. This of course applyes to all the moving and rotating parts in the engine.


More precise fuel injection

The power generated by any gasoline engine comes from the fuel burned inside the combustion cambers. Fuel needs oxygen to burn though and that oxygen comes from the air. So, what is the best possible fuel/air ratio? That question has three answers, and all them are correct in one way or other..

When the air/fuel ratio is 14,7:1 (14,7 grams of air for every gram of fuel) the engine is burning optimally. If the car has catalytic converter, you must use 14,7:1 ratio (Lambda=1) or the cat will die. When the air/fuel ratio is 15,4:1 (Lambda 1.05) is the driving most economical. (Best choice if you want to save gasoline) However, if it's the maximum power you are looking for, the air/fuel ratio should be 12,6:1 (Lambda 0.86). The fuel/air ratio is not static, it changes depending on how much you floor the pedal on the right...

The more precise the fuel/air ratio is, the more you can get out from the engine. Fuel injection system is generally more precise than carburettor, therefore with injection system it is possible to get more power and better fuel economy.


More precise ignition timing

The spark plug need to be fired a little before the piston reaches top dead center, because it takes a while before the mixture burns and starts to push the piston down. The ignition advance is measured in crank degrees rather than seconds or milliseconds.

The amount of ignition advance required depends on the engine design and on engine speed. The faster the engine is revving, the more advance there must be. Generally most engines are out of tune, so you might gain some power by adjusting the ignition.


Written by: Tuomas Kuisma © FFp Motorsport 2000-2002



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