Engine Power Curves - From The Dyno To The Racetrack

The use of a dyno to measure horsepower and torque is a valuable tool for the racer. If you use the dyno just to see what kind of torque and horsepower numbers your engine is developing, that may be an interesting data point and a conversation starter but it really diminishes what you can learn from this tool. The measurement of the torque the engine produces and the calculation of horsepower is only one small part of the equation.

Once you have the information, developed the best power settings, and are confident that your time on the dyno has maximized a given combination it is now time to take the engine to the track and see what you can do with what you have learned. The new knowledge you have gathered will or should be driving changes to the car and possibly to even how you drive the car.

We were able to take part in a dyno test at RPM Engine Development in Chandler, Arizona. This particular engine was going to be raced in the Renegade Sprint Series and is a very heavily regulated 315.9 max cubic inch small-block Chevrolet. Series rules mandate a GM 305 block (you have a choice of 10 different casting numbers) with a spec 305 head, a max compression ratio of 10.25 to 1, flat tappet cam, and constant flow butterfly type fuel injection. Plus, all engines in the Renegade Sprint Car Series must be inspected and sealed prior to competing in any scheduled racing event.

The particular engine combination we are testing is designed more for durability, longevity, economics, and to keep the field even from a power perspective. It was not designed for all out power production. The intent of this dyno run was to develop a better understanding of the power produced and then make adjustments that were legal and within the scope of the rules. It is interesting to note that none of the seals that were in place on the engine were removed as part of the test, and engine legality was never violated.

Once you leave the dyno you should be armed with some documentation gleaned from the dyno runs. You need to be concerned not only with the peak power but where the torque and horsepower numbers are versus engine rpm. These critical bits of data are just what you paid for. Often times the data will be formatted in columns of numbers. While this is useful information, changing the presentation of the data into a series of graphs that illustrate the shape of the curve is sometimes a better way to display the data. It is the shape of the curve or curves that we are really concerned about. The shape of this curve will help you to better visualize the maximum usable engine power and the rpm where it occurs. It is far too simple to just look for the big numbers and miss what the data is really saying. The key is the shape of the curve and the range of usable power.

Just a small caution about data presentation and the potential for statistical gamesmanship as it pertains to data analysis. There are many ways to present data, what needs to be remembered is the data is what it is and no more. Please avoid the temptation to make what you have more than it really is. The quest for speed and power is not about the big number that you can get by playing with, shaping, smoothing, or massaging the data to try and see something that is just not there. It is all about taking what you can learn about the test session you just completed and understanding the power and how you can best use the information, nothing more. Do not let yourself be seduced by the quest for the "big" number. Avoid the dark side.

Prior to putting this information to use, let's talk about the dyno runs.