Secrets About Horsepower and Torque We Should Understand

What is horsepower? What is torque? By definition 1 hp equals 33,000 ft-lbs per minute. This was determined by a British engineer by the name of James Watt. It means lifting 1 pound 33,000 feet up in one minute or 33,000 pounds through one foot in a minute or basically any combination that multiplies out to 33,000. Here is the equation to find hp. Horsepower= work done per minute
33,0000

Engines rotate, so we need to figure the work done in a circle rather than a straight line. To do this we need to do a little math to get the job done. We begin by finding the crank radius in feet. Multiply the crank radius by PI (3.142). Then multiply that by 2. then multiply that by the force in pounds created from cylinder pressure and RPM's. It should look something like this when set up. ( R x 2 x 3.142 x F x RPM )
33,000

If we multiply the radius by the force we get the torque. This means we can simplify the equation something like this. ( 2 x 3.142 x Torque x RPM )
33,000

To put it simply, we have discovered a simple formula for hp from this work. By dividing the top by the 33,000 on the bottom we discover that a easier way to solve this equation is this: ( Torque X RPM )
5252

let's look at how to measure horsepower now that we understand where it came from. A Dynamameter is used to measure horsepower. This is more commonly referred to as a dyno. The dyno applies resistance or a braking force to the engine. It does not measure horsepower in a direct sense, rather it measures torque at a given RPM and the calculates horsepower from these two known values. Torque X RPM's gives us power, but horsepower is not the same as power. To find our results in the form of horsepower we must divide by a constant, that being 5252. An example of calculated hp for a engine that produces 400 ft-lbs of torque at 7000 RPM would look like this . 400 x 7000
5252 = 266.6 hp

With this information we can safely say that if we were to double the torque at the same RPM the power will double, and if we double the RPM and don't change the torque the power still doubles. So we see that any change in torque will also change the horsepower.

Torque from an engine is exactly the same as torque from the torque wrench we use to put engines together. Torque is merely ( Force x Radius ). In an engine the radius is the same as half the stroke, and the force is the average from the gas pressure pushing down on the piston. Gas pressure comes from filling the cylinder with air and heating it up with burning fuel. There natural limits as to how much torque an engine can produce set forth by the fact that atmospheric pressure is 14.7 psi at sea level. So, how do we boost this up? Forced induction such as a supercharger will fill the need to overcome this hurdle.

Now that we have a better understanding of horsepower and torque lets find out how to make the most of both of these. There are always limits to everything, so before going to make as much as we can, let's know some limits to consider as we journey into making horsepower and torque.

When building hp you need to give the engine as big a breath of air and fuel as possible to fill the cylinders and get rid of the burnt up gases as quickly as possible.Heads, intake, carb, supercharger, and induction all play a part in the process. Consider all the factors to build hp and torque. Bigger may not always be better. So can you replace cubes or is the old adage true. I think it is busted as you can build mass hp from a small block as I have built a 408 sbc that produces 590 hp while sipping on pump gas. Of course this didn't happen easily and I spent a great deal of money to get this to happen. Know your spending limit and then start to form a plan to build your engine to be a strong as you can make it. Learn from others and save yourself time and money from mistakes that don't work or yield minimal results.

David Vizard's How to Build Horsepower