Forum: HoseHeads Sprint Car General Forum (go)
Moderators: dirtonly  /  dmantx  /  hosehead

According to Wikipedia:

Horsepower (hp) is the name of several units of measurement of power, the rate at which work is done. The most common conversion factor, especially for electrical power, is 1 hp = 746 watts. The term was adopted in the late 18th century by Scottish engineer James Watt to compare the output of steam engines with the power of draft horses. It was later expanded to include the output power of other types of piston engines, as well as turbines, electric motors and other machinery.^[1][2] The definition of the unit varied between geographical regions. Most countries now use the SI unit watt for measurement of power. With the implementation of the EU Directive 80/181/EEC on January 1, 2010, the use of horsepower in the EU is only permitted as supplementary unit.

It goes on to say....

Relationship with torque

For a given torque and speed, the power may be calculated; the relationship between torque in foot-pounds, rotational speed in rpm and horsepower is:

Where is power, is torque, and is rotations per minute. The constant 5252 is the truncated value of (33,000 ft·lbf/min)/(2? rad/rev).

So what does all this mean?

Well, to me it means two things: 1.) Horsepower is the rate at which work is done, and 2.) Horsepower is CALCULATED.

The calculation for Horsepower is all based upon Torque and RPM.

hp = (Torque x RPM)/5252

Here is an example. One of my really good engines makes 586 ft lbs of peak torque and 602hp at 5400 rpm. It makes 472 ft lbs of torque and 683 peak hp at 7600 rpm. This engine was dyno'd at Jay Eckley's on a Superflow dyno with WinDyn Software and has won races at Knoxville, I-80 and other various tracks. This engine will not turn over 8600 rpm on the track unless the u-joint or drive line break.

(586 x 5400) / 5252 = 602hp

(472 x 7600) / 5252 = 683hp

However, if we built a completely different engine, with the exact same torque numbers, but just moved them up in the RPM range by 1000 rpm - THE RESULTS ARE SPECTACULAR.

Using the same equations but moving the rpm up result in the following:

(586 x 6400) / 5252 = 702hp

(472 x 8600) / 5252 = 773hp

By significantly modifying the "powerband" of this engine we have made an additional 90hp. Interestingly, the torque numbers have remained constant. But, by moving them up 1000 rpm we can perform more work in the same amount of time.

IN MY OWN HUMBLE OPINION... the reason we are seeing such significant increases in horsepower numbers is because of the increase in operating rpm of the engine - moving the torque band up in the engine.

There is no way that this trend can save us as racers any money. We are either faced with keeping up with the competition or not. The bar has been set pretty high at this point in time.

PISTON INERTIA: http://www.wallaceracing.com/Calculate-Inertia-Force-of-Piston.php

A 450 gram piston at 8600 rpm with a 3.5" stroke and a 6.000" rod = 3647 pounds of force

A 450 gram piston at 9600 rpm with a 3.5" stroke and a 6.000" rod = 4545 pounds of force
(that is an increase of 24.6%)

Even a 420 gram piston at 9600 with a 3.4" stroke and a 6.200" rod = 4121 pounds of force (that is an increase of 13%)

MB

Rome wasn't built in a day......but they sure didn't
waste any time burning it down!

 
 
 
They don't even know how to spell sprint car 
much less chromoly...http://www.ycmco.com

Informative. Well said!

That is a good read Mark.

Our pistons are 459-460 gram JE units. 9600 is just a rumor. 9100 is more realistic. Peak hp is at 7900rpm, peak torque at around 5800rpm. We can move the cam around to manipulate these points. More torque, less HP or more HP, less torque. Its all about what feels good to the driver.

A 17-hand horse strong enough to pull a plow. That, my friend is HORSEPOWER!

 
I LEARNED ESP FROM MY MOM

"PUT YOUR SWEATER ON: DON'T YOU THINK I KNOW WHEN 
YOU'RE COLD?"