Wolfpack Speed
12-14-2007, 11:57 PM
Im trying to have a dyno up and running at the shop sometime in 2008. I have been speaking with Dan Hourigan and thought I would pass this attachment along for anyone interested..
Truth, Lies, and Dyno Runs
Part 1
A popular thread that continues to surface in various enthusiast forums is related to the results attained from various chassis dynos. In the following paragraphs, I’ll attempt to explain the various types of chassis dynos and their operating principals, how they’re used in the field, and how to interpret the results. I know that you’re thinking, “oh boy, the VP of Dynojet is going on a sales pitch”, and that couldn’t be further from the truth. I’m an avid automotive enthusiast, and no, that doesn’t mean I just plop down cash for the latest exotic car. I’ve made thousands of dyno runs, tuned 1000’s of automotive ECM’s, designed and fabricated my own turbo kits, and made hundreds of passes at the strip. I hope to educate the sometimes confusing subject of chassis dynos and how they’re used in the field.
There are generally two types of dynos that are used for performance verification and tuning, “inertia type loading”, such as the Dynojet 224x or 248, or “electric type loading”, such as a Mustang 250, 1100, Dyno Dynamics, or Dynojet 224xLC / 424xLC. Traditionally Dynojet has offered the inertia loading dynos, whereas Mustang Dynamometer and Dyno Dynamics have been electric type loading dynos.
The major differences in the two types of dynos are their principals of operation. A true inertia dyno (such as the Dynojet 224x or 248) uses large steel rollers that contain mass. This mass is fixed, it can never change, and for those that remember high school physics, Force = Mass x Acceleration. Based on the time that is required to accelerate a mass (the steel drums in this case), you are effectively measuring force. OK, so now that we have force, how does an inertia dyno come up with horsepower, simple, force (lbs) multiplied by speed (ft/sec) effectively yields horsepower. Since every Dynojet dyno on the face of the earth has a mass that has been precisely quantified using a proprietary process, and that value is stored in the dyno software for each dyno, not only are the horsepower numbers consistent every morning, noon and night, but each and every Dynojet is relative to one another. Go ahead, take your car to 25 different Dynojet dynos, run it up, and I personally guarantee the horsepower will repeat to within 1/2 HP (no one else would dare make that claim). What if the numbers aren’t the same between the 25 Dynojet dynos, well, it’s quite simple to explain, and you need look no further than the vehicle. Most modern powertrain management systems have a lot of authority when it comes to how much power they ultimately put to the wheels. Capturing OBD2 parameters such as spark advance, engine coolant temperature, inlet air temperature, mass air flow, and other critical PID’s provide the insight required to determine why the vehicle did, or did not repeat.
So let’s take a step back before we move on and look at this from a practical perspective. As an enthusiast, you may be wondering, “what are the variables that exist when I dyno my car on a Dynojet, there has to be something”. I would respond, “A Dynojet dyno operator CAN NOT change the data that determines what the power reading will be (remember the physics thing?). What ever power is being put to the drums will be measured and displayed, period.” Once that power has been measured,there are two ways to look at it, corrected or uncorrected. Since every Dynojet dyno is equipped with electronics that measure the atmospheric pressure, temperature, and humidity, the results are able to be analyzed as a “corrected value”. This allows an “apples to apples” comparison when testing in regions that are at different altitudes, which affects the atmospheric pressure, and different temperature. This is also important for comparing results at the same dyno shop, for example, here in Las Vegas our atmospheric pressure stays relatively consistent, but our temps vary from 38 degrees to 118 degrees. So the same car with no changes will certainly make less power on the hot day compared to the cool day, but applying the SAE CF allows us to make an “apples to apples” comparison. If you take anything away from the last few sentences, it would be to ask your dyno operator to make sure that he is showing you SAE corrected HP figures, and before I get off my soap box, I will say that there are certain Dynojet dyno owners who apply the “STD” correction factor, and that’s not proper to do. The STD CF is an older standard that yields slightly higher HP numbers, so don’t allow yourself to fall into the trap (just use the SAE CF!!).
Truth, Lies, and Dyno Runs
Part 1
A popular thread that continues to surface in various enthusiast forums is related to the results attained from various chassis dynos. In the following paragraphs, I’ll attempt to explain the various types of chassis dynos and their operating principals, how they’re used in the field, and how to interpret the results. I know that you’re thinking, “oh boy, the VP of Dynojet is going on a sales pitch”, and that couldn’t be further from the truth. I’m an avid automotive enthusiast, and no, that doesn’t mean I just plop down cash for the latest exotic car. I’ve made thousands of dyno runs, tuned 1000’s of automotive ECM’s, designed and fabricated my own turbo kits, and made hundreds of passes at the strip. I hope to educate the sometimes confusing subject of chassis dynos and how they’re used in the field.
There are generally two types of dynos that are used for performance verification and tuning, “inertia type loading”, such as the Dynojet 224x or 248, or “electric type loading”, such as a Mustang 250, 1100, Dyno Dynamics, or Dynojet 224xLC / 424xLC. Traditionally Dynojet has offered the inertia loading dynos, whereas Mustang Dynamometer and Dyno Dynamics have been electric type loading dynos.
The major differences in the two types of dynos are their principals of operation. A true inertia dyno (such as the Dynojet 224x or 248) uses large steel rollers that contain mass. This mass is fixed, it can never change, and for those that remember high school physics, Force = Mass x Acceleration. Based on the time that is required to accelerate a mass (the steel drums in this case), you are effectively measuring force. OK, so now that we have force, how does an inertia dyno come up with horsepower, simple, force (lbs) multiplied by speed (ft/sec) effectively yields horsepower. Since every Dynojet dyno on the face of the earth has a mass that has been precisely quantified using a proprietary process, and that value is stored in the dyno software for each dyno, not only are the horsepower numbers consistent every morning, noon and night, but each and every Dynojet is relative to one another. Go ahead, take your car to 25 different Dynojet dynos, run it up, and I personally guarantee the horsepower will repeat to within 1/2 HP (no one else would dare make that claim). What if the numbers aren’t the same between the 25 Dynojet dynos, well, it’s quite simple to explain, and you need look no further than the vehicle. Most modern powertrain management systems have a lot of authority when it comes to how much power they ultimately put to the wheels. Capturing OBD2 parameters such as spark advance, engine coolant temperature, inlet air temperature, mass air flow, and other critical PID’s provide the insight required to determine why the vehicle did, or did not repeat.
So let’s take a step back before we move on and look at this from a practical perspective. As an enthusiast, you may be wondering, “what are the variables that exist when I dyno my car on a Dynojet, there has to be something”. I would respond, “A Dynojet dyno operator CAN NOT change the data that determines what the power reading will be (remember the physics thing?). What ever power is being put to the drums will be measured and displayed, period.” Once that power has been measured,there are two ways to look at it, corrected or uncorrected. Since every Dynojet dyno is equipped with electronics that measure the atmospheric pressure, temperature, and humidity, the results are able to be analyzed as a “corrected value”. This allows an “apples to apples” comparison when testing in regions that are at different altitudes, which affects the atmospheric pressure, and different temperature. This is also important for comparing results at the same dyno shop, for example, here in Las Vegas our atmospheric pressure stays relatively consistent, but our temps vary from 38 degrees to 118 degrees. So the same car with no changes will certainly make less power on the hot day compared to the cool day, but applying the SAE CF allows us to make an “apples to apples” comparison. If you take anything away from the last few sentences, it would be to ask your dyno operator to make sure that he is showing you SAE corrected HP figures, and before I get off my soap box, I will say that there are certain Dynojet dyno owners who apply the “STD” correction factor, and that’s not proper to do. The STD CF is an older standard that yields slightly higher HP numbers, so don’t allow yourself to fall into the trap (just use the SAE CF!!).