Gotta Need for Speed? Steps to Increase Your Car’s Horsepower

You can’t have your cake and eat it too – in most cases, more power decreases fuel mileage. There are some exceptions to this rule. Muscle cars – mid-size vehicles from the late ‘60s and early ‘70s, have high horsepower. The horsepower is relative to the weight of the vehicle. The more the vehicle weighs, the more power you need to keep a certain speed rating. In racing circles, it is well known that every 100 pounds of weight decreases measured speed – usually the time it takes to go one-quarter mile – by one-tenth of a second.

Engines are built to certain specifications for horsepower, torque and weight. The average vehicle might weigh in at under 3,000 pounds and have low horsepower – about 110 average horsepower. These vehicles usually have excellent fuel mileage.

What Makes a High Performance Engine?

Vehicles that are considered high performance include the 2005 Mazda RX-5 and the 2008 and 2009 Chevrolet Cobalt SS. You could also make your own high performance vehicle. Here are a few “high performance” picks from Popular Mechanics, manufactured between 1965 and 1971:

• Chevrolet: Chevelle, Camaro and Nova
• Dodge: Challenger and Charger
• Ford: Mustang

There are many more, but these were the popular models that had the auto world buzzing. Auto technicians often rebuilt the engines in these vehicles with high performance parts. The engine blocks were often bored and stroked, says HotRod.com. When you bore an engine, you increase the diameter of the cylinder. You can stroke an engine by using a shorter piston and longer rod or vice versa.

Building a high performance engine can be expensive. Pistons should be lightweight aluminum to decrease the weight in the engine. Rods should be “pink” or “x” rods, if you are using Chevrolet production rods. If not, you can purchase a number of strengthened rods from other manufacturers.

If you’re going to go all-out and stick a blower on top of the engine, you’ll definitely need a steel crankshaft with double keyways. Cast crankshafts crack under the pressure the blower puts on the engine. Plus, keep in mind, that anything sticking out of the hood of your vehicle is illegal in many states. The camshaft and heads also play an important role in creating a high performance engine.

Putting it All Together

You can’t just buy parts and throw them at the engine. Everything has to fit just right. If you buy a camshaft with three-quarters of an inch of lift, you need heads and pistons that will handle the camshaft. Keeping the valves open longer (duration) requires larger valves in the heads. Remember, what goes in, must go out. As the camshaft opens the valves, the vacuum in the engine sucks in air and fuel. If the duration is too long and you don’t have an adequate fuel supply, the engine is going to bog.

That philosophy applies to parts as small as a rubber seal. If you remove a metric o-ring that is .20 by .20, you better replace it with the same size (you can double check these by using a metric o-ring chart, which Apple Rubber has on its website).

A larger lift may require dished pistons instead of flat-top or domed pistons. The lift moves the valves further into the cylinder; and two things cannot occupy the same space at the same time. Too much lift with the wrong piston could result in cookie crumbs at the bottom of the piston hole and in the oil pan.

You also have to get the combination just right. Just because you put domed pistons in the engine doesn’t mean you are going to significantly increase horsepower. Everything must match. Since one part affects another part in the engine, you usually won’t have much increase in horsepower or toque by replacing one part of the engine.

With today’s vehicles, it is not as easy to make more horsepower because of the computers. Whenever you make changes to the system, you’ll have to program the vehicle’s ECM/PCM to the change in values created by high performance parts. Before computerized engines, it was very easy to double or even triple the horsepower in some engines by changing pistons, valves, heads and the camshaft to increase compression – or by adding a roots-type blower or supercharger.