Somebody I know once said this:
I have recently seen many topics that discuss dyno testing included as part of the discussion. While everyone has opinions on where, who, what kind of dyno to use or is best, what bothers me is the misinformation being discussed. What I hope to do is clear up some of this misinformation with observations I have personally seen.
1st – The Peak HP and TQ numbers you receive are just that. Numbers. They don’t tell the whole story. Whether corrected or not, the numbers don’t represent how well the truck performs across the entire RPM band. Each of you should look at and compare to previous runs the curve. When we tune a truck, this becomes as important as the actual numbers. On the electronic motors, this is less of an issue but is critical on the mechanical motors.
2nd – Correction factors. We all agree, these were not designed for forced induction engines. While they do help in leveling the playing field, they cannot be regarded as the absolute truth for comparing one truck/machine to the next. They can be used to compare on the same day/same machine. They can also be used pretty decently to compare at the same location, runs from different conditions between summer and winter. Here is where everyone needs to understand the differences. If you compare SAE corrected numbers, understand correction factors will vary from location to location, and day to day, or even hour to hour. A truck that makes 495hp with a 10% correction factor will be 450 without the correction. So if you dyno at another location with a 1.0 correction (meaning no correction change) and all else being equal, you will dyno around 45hp less than your previous runs at 1.10 correction. And since this is a percentage, a 700hp uncorrected run could be 770 with a 1.10 correction. See how some can be disappointed? But regardless of the correction, the lines should still be the same, meaning power delivery should be the same. Also understand that when we dyno at the track, you cannot use SAE correction to calculate your MPH on the strip. If we have a 1.10 correction, then we need to use the uncorrected numbers for trap speed. Uncorrected means what the vehicle ACTUALLY made to the rollers. So that is what you will ACTUALLY make on the strip. More on this later.
3rd – Loading vs Inertia. This one will be disputed forever. Some prefer to load while others prefer not to. I prefer inertia for my needs and here is why, but it shouldn't take away for the loading dynos. It is just MY preference. When running on my dyno, I can tell how well the motor is tuned. I can tell how well the turbo(s) respond which means I can tell how well the truck works in real world driving. If the truck won’t light on my dyno, it tells me the truck is laggy on the road. If you are a sled puller, not an issue. If this is a drag racer or street truck, it is. There is a myth that you cannot get enough load with a dyno jet with big turbo’s. It is true I have found some trucks that don’t work well on my machine, but was it the dyno’s fault. If I can make a large set of twins make 100 psi on my machine, or have a HX40/3B combo make 80 psi on the dyno, wouldn’t you agree I am working the truck? But understand, they were tuned on the dyno. They were not built then magically went on the dyno and did it. Any factory turbo’s will not have a problem on an inertia dyno. I have never had a case where stock turbo’s were a problem. As a matter of fact, in most cases only big singles have been a problem, and again, most of those could have been improved with tuning. What I don’t want to see happen is someone being convinced an inertia dyno will not provide accurate results when it may be they have a poorly tuned truck. Loading can mask these issues. Loading will bring the turbo(s) up but again, this can mask a tuning issue.
Loading dyno’s also require the operators to include run parameters so the software can accurately calculate. If the operator provides “rough estimates” with these parameters, then your results will be “rough estimates”. There are operators that are very competent and this is a non-issue. But there are some that are not. A Dyno Jet operator cannot change the run numbers with the exception of correction. I can choose between SAE, STD, DIN, EEC, etc but even with those, I cannot select how much correction to add. The dyno does that based on the weather station readings. This is one reason why the dyno jet is regarded by most as the most accurate from dyno to dyno. But I also want to express, there are loading dyno’s that I believe are run very well, deliver comparable numbers to my dyno and others.
Dyno Testing and to the Street/Strip
When I run trucks on the dyno, and they then are tuned to perform on the Dyno Jet, they usually become some of the sweetest trucks on the street you will drive. I’ll use Matt Stuckey’s truck as an example. Jeff has it tuned to 720-740 uncorrected hp on my dyno through the factory intercooler and a 40/3b combo. This truck makes 80 psi on the street, and 80 psi on the dyno. This truck will spool the turbo’s very well and as a result, on the street it is one of my favorite trucks to drive. Power is there anytime, without this awful lag to overcome. This makes everyday driving an absolute riot.
I use www.smokemup.com
as the calculator to predict what these trucks will trap at. So far, this is the best one I have found. You will hear from many these don’t work for our trucks and to be honest, they are not perfect. But they are not perfect for the gassers either. Here is why. The algorithms used for these calculators cannot see the HP/TQ curves of your motor. All they know is your mph and vehicle weight, from which it will calculate your estimated rwHP. So if you make peak hp at 2500 rpm, but run down the track between 2700 and 3400 do you think it will be accurate? Racers should use the curves from a dyno run to determine how to run their truck down the strip. Meaning where the fat or the power curve is and where you need to operate the engine to deliver the most power for 1320 feet. When this happens, you might be surprised to see how well the calculators are at validating your dyno runs. Last year, I predicted what Jeff’s drag truck, Matt truck, and Darren’s truck would run before they ever made a pass. I gave each a 3 mph window and I hit each dead in the middle. You cannot use these numbers and calculators to estimate ET. There are way too many variables. This calculator cannot over come what diesel torque and a 4wd launch will do to a 6000 lbs truck. An example using my truck. It made 440 uncorrected hp on my dyno. It ran a 13.89 @ 98 mph in 4wd. Best 2wd run was 14.7 @ 98 mph. Using the calculator I get 429.3hp with ET on the 2wd run, I get 508 on the 4wd pass. Using MPH, I get 441hp on both. Again, these calculators should be another TOOL to assist you in getting the maximum potential out of your truck.
In conclusion, I just want folks that don’t know, what benefit you can get from these tools, and I want to clear up those that say if you don’t load, don’t bother, or call a dyno jet, dyno junk, or blame a dyno for results that don’t meet the owners expectations. My suggestion is to instead of doubting the findings, try to explain WHY you had the results you had. If you run on my machine, and I believe we have left HP on the table, I will tell you. I will even go so far as to point you in the direction with the dyno sheet to a person that can help if I know. If you are not willing to listen, then you will always be chasing those that do listen and learn whether it is from me or someone else. And finally, there has been discussion on direct drive vs OD runs. On a Dyno Jet with a turbo diesel, it is suggested you use top gear. When loading it is suggested you use direct drive (1to1 ratio). I have done both on the dyno jet and the HP may vary a couple of HP and the TQ will be slightly higher in top gear. Where a problem will arise is with trucks with speed limiters. The newer trucks are tuned to make peak power near 3000 rpm. If I cannot reach that rpm in 5th gear then I will not see max power. A Duramax will make roughly 240hp in 5th against the limiter at about 2700 rpm and the curve is still on the rise. Just removing the limiter to allow the spin to 3200 will result in another 10 to 20 hp on these trucks. Unless there is a tech II or equivalent to hold the truck in 4th, this will be the case. So, what I am saying is if someone baselines stock with a speed limiter, they will dyno lower than another person that has removed the limiter with a programmer but not added any power.
Hopefully this will explain to some the dyno experience a little better for some. This is supposed to be fun and a learning experience. Nothing I hate more than to have someone unhappy after a dyno run. If I could make everyone have 800hp I would, but then you’d be wondering why you are not making 10 second ¼ mile passes.