88 Ford
Full Access Member
I've always considered dyno tests (as well as any other forms of testing) one of the more interesting parts. As a "do it myself" sort of guy as well as someone who actually runs tests, I'm always interested in the effects of design change. However, as the years have gone by, I find myself less and less impressed by the dyno tests provided. Now, I often find myself more disappointed, disillusioned, and even disgusted with what is being said. Instead of reading a well thought out design discussion that is accompanied by well executed backup tests, I often feel like I'm reading information provided more to motivate somebody to spend money, incomplete discussions that left out information that really needed to be known or created more questions in my mind than gave me answers, discussions that, to me, were "tilted" or biased rather than neutral in position and sometimes, in my mind, even determined or affected the tests' outcome, comments that obscured truths, procedures that protected a product that had one or more design flaws, opinions that could be as misleading to some as they might be helpful to others, etc. The following discussion is not based on any one immediate situation but on hundreds that I've been witnessing for years. This following discussion is also going to disturb many who read it so you are being warned, up front, about that possibility.
Problems with dyno testing.
There are no industry standards on dyno testing procedures to assure consistency of results that allow accurate comparison. While the data from sensor readings taken during a dyno test are usually CORRECTED to a specific temperature and barometric pressure to make comparisons easier, the manner in which the test(s) is/are run can vary considerable from one dyno cell to another, from one dyno operator to another, even reasons why test(s) were run in the first place, etc. - can create enough difference in outcome that just comparing numbers from different tests might end up being very misleading.
For example, while the best way of running a dyno test might be with open collectors (assuming the engine is going to be used that way), the reality many shops have to face is that they are in or near residential areas so dyno testing has to be conducted with some sort of exhaust system. Now one must be concerned not only about how the basic exhaust systems differ from shop to shop (what mufflers are used as well as how many), how different in size the flexible tubing BETWEEN the pipes and the rest of dyno cell's exhaust system might be, (These differences might not seem important to many but I remember arguments between some fellows in this area about "so and so's" dyno reading 25 HP higher than some others' dynos and that, to some, meant he was using a different CORRECTION (altitude and barometric pressure) factor to make his engines look like they were making more horsepower and torque. When I pointed out to them that I thought "so and so's" exhaust system may be better thought out than others, these fellows said that they had never thought of that possibility. So, in effect, they were accusing him of cheating when that may not have been the case at all.)
Not to downgrade any dyno results anyone as but this so true! For some reason as far as how our diesels are geared even compared to newer ones, I think dynojets might read a lil bit lower than the actual hp. Idk though. But anyway it got me wondering that after I read the little dyno article NMB2 posted. It said, "Inertia dyno's work on the principle of the acceleration of a known mass over time. Their rollers are the known mass. Weighing in at over 2500lbs or so." First off our truck are not meant to be quick accelerators due to gearing and the rev limit cus they are diesels. It said the faster you can accelerate the rollers the more horsepower the dyno would read. So, due to this if you changed to a different gear set, it could alter the results. Secondly, there is only a 2500 lb load on a Dynojet. That definitely will not load our truck simply due to the fact that our trucks weigh a hell of a lot more and it doesn't take into account wind resistance and other factors. The lower load on the truck will lead to smaller numbers overall than if we were driving it on the road.
Also, I have heard it mentioned about tuning of our trucks. What can be done as far as tuning other than timing the truck and setting the fuel screw? I'm not the most knowledgeable at all on this subject. Lol