I'm starting a new thread for conversation about dyno-specific topics so we don't clutter the other thread with posts that are not specific to the OP.

One of the first lessons I learned when I got into modifying cars is that dynos are different, and it is well-known that Mustang Dynos read low compared to others. It's possible that some tuners have recalibrated their Mustang Dynos to read similar to others, like DynoJet. But for the most part, Mustangs read low. Tons of examples of this can be found by googling "Heartbreaker Dyno"... Here's a post I found that provides good info.

"I have written pages and pages of posts on this topic on various forums. Here's a little write up I did a few weeks ago. . .

DynoJets are inertia dynos, and have been around for years, much longer than any type of load cell dyno. 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. Your car gets strapped down to the machine, and the dyno collects it's data. It is able to calculate horsepower by measuring the acceleration in rpm of the rollers in regards to RPM. This is why gearing can affect the dyno results, more on that in a bit. Now that the dyno has recorded the horsepower curve, it can take the integral of that curve and get the torque curve. Since the dyno’s power calculations are based on the acceleration of mass over time in regards to RPM, gearing is very important. Since a vehicle with a lower gear ratio can accelerate the mass to a higher speed using less engine RPM, it will show a higher horsepower number than a car with a higher gear ratio. If a car is able to accelerate the dyno’s rollers from 200rpm (roller) to 300rpm (roller)in 1500rpm (engine), then the dyno is going to record more power than a car that did that in 2000rpm (engine).

Now we go to Mustang dyno’s and other loaded dyno’s. Our Mustang MD-1100SE dyno’s rollers weigh 2560lbs. That is the actual mass of the rollers, much like the DynoJet. That’s about where all the similarities end. When we get a car on our dyno, we enter two constants for the dyno’s algorithms. One being the vehicle weight, the other being what’s called “Horsepower At 50mph”. This is a number that represents how much horsepower it takes for the vehicle to push the air to maintain 50mph. This is used as the aerodynamic force. Mustang dyno’s are also equipped with a eddy currant load cell. Think of a magnetic brake from a freight train. This magnetic brake can apply enough resistance to stall a big rig. Off one side of the eddy currant load cell, there is a cantilever with a 5volt reference load sensor (strain gage). As the rollers are spinning this load sensor is measuring the actual torque being applied. So as the rollers spin, the load sensor is measuring the force being applied, sending that information to the dyno computer, taking into account the two constants entered earlier, computing the amount of resistance needed to be applied to the rollers to load the car so that the force of the rollers resistance is as close to the force the car sees on the street. The dyno is then able to calculate the total force being applied to the rollers in torque, and then taking the derivative of that torque curve to arrive at the horsepower curve. Since torque is an actual force of nature, like gravity and electricity, it can be directly measured. Horsepower is an idea that was thought up by man, and cannot be directly measured, only calculated.

I like to state it like this. . . I start by asking how much your car weighs, lets say 3500lbs. Now you take your car and you make a make a WOT rip in your tallest non overdrive gear, how much mass is your engine working against? 3500lbs right? Now you strap your car on a DynoJet and you make a WOT in the same gear, how much mass is your engine working against? 2500lbs right? Now you strap your car on a Mustang dyno, how much mass is your engine working against? 2500lbs. Plus the resistance being applied by the eddy current generator. We’ve seen anywhere for 470lbs of resistance to over 700lbs of resistance as measured in PAU force in the data logs. So which one is more accurate? Well they their both accurate. If a DynoJet dyno says you made 460rwhp, then you made 460rwhp. If a Mustang dyno says you made 460rwhp, you also made 460rwhp. Now which one of those numbers best represents what your car is doing when its on the street. That’s a different question.

The most important thing to remember is that a dyno is a testing tool. If the numbers keep increasing, then you’re doing the right thing. We try to look over at NET gain, instead of Peak HP numbers. A 30rwhp increase is a 30rwhp increase regardless of what dyno it is on.

Now I can address how to calculate the difference between one type of dyno and another. Simply put, you can’t. Because Mustang dyno’s have so many more variables, it’s not a simple percentage difference. We’ve had cars that made 422rwhp on our Dyno, two days later make 458rwhp on a DynoJet the next day. We’ve also had cars that made 550rwhp on our dyno, make 650+rwhp on a DynoJet a few days later at another shops Dyno Day. For instance, my 2002 Z28 with a forged internal LS6 Heads/Cam/Intake, makes 460rwhp on our dyno. I thought that was a little low, since I’ve had cam only LS6 Z06 vettes make 450rwhp. So I overlaid the dyno graphs. Guess what, the PAU force for my car was almost 200lbs more than the C5Z06 that made 450rwhp with cam only. So I entered the weight and horsepower at 50 number for a C5Z06 and did another horsepower rip with my car. The only reason I did that was to compare Apples to Apples. This time my car made 490rwhp, no other changes. Now I don’t go around saying my car made 490rwhp, I say what it actually did with the correct information entered into the computer. It made 460rwhp. Now if I ever get a chance to take it on a DynoJet (which I plan to in the spring), I have no doubts it’ll be over 500rwhp. I know this based on airflow and fuel consumption on the data logs.

But since we’re asked this question constantly we're fairly conservative, and hence tell our customers that the difference is closer to 6-7%, but as you make more power, and the more your car weighs, the difference increases as well. You must remember, Dyno's regardless of the type are tuning tools, and are in no means meant to tell people how fast their car is. Now which one is more "real world" is a totally different question. I like to explain it like this..... If you drive your car in a situation in which you have no mass and you're in a vacuum, so basically if you do intergalactic racing in space, use a DynoJet. If your car sees gravity, and has an aerodynamic coefficient, and you race on a planet called Earth, then use a Mustang Dyno"

 

(to the fellow you copied this from on an other auto forum)
if you are going to write "pages" on the topic, I would hope that you get it right, or you are going to do a LOT of correcting!
So, lets get right into it. Ill just respond here regarding the dynojet, because it is most simple.
NO, you don't need to know what gear you are in, nor do you even need to have a RPM reading. if you are in 1st gear or 6th gear, the dyno doesn't know or care, but the computer system with sensors telling it how fast the drum is going at any given time, will be able to easily calculate power. why???? because power is the rate of change of kinetic energy. if the drum is accelerated in 1st gear quickly, its doing it over a lower speed. The same power would be measured. And if the speed is higher in a taller gear and the rate of acceleration is slower. Its proportionally slower by the way, because at any same power, acceleration is inversely proportional to speed. so, if its 5th gear or 1st gear, the dynojet can measure, VERY ACCURATELY, the power you make without knowing RPM of the engine, or what gear you are in! (so, contrary to your point, gearing doesn't effect HP output) The graph would be HP vs MPH. with a spark, you get RPM and you get HP vs torque. In both cases, no need to know what gear you are in. It doesn't matter! gearing DOESNT effect the dyno result, and without a RPM value to plot against the HP curve, there is no way the dyno can calculate torque. But, with RPM known, and the HP curve plotted, torque can be plotted against iit. otherwise, there is no way that the dyno knows if you are a 10,000rpm Porsche 500hp300ftlb engine, or a 5000rpm 500hp 600ftlb viper engine. the HP curve might look very similar!


BTW - you don't integrate power and get torque. you get force..... that's at the tires... torque at the engine can be almost anything!


make sense???


Next, Ill address the brake dynos.

 

[bracing for spirited debate]

 

You better do your homework here


Love the discussion though.. always fun to go through power /torque discussions! lots of confusing information on the internet of the subject.


let the fun begin!

 

There's no debate. You have fact (what XWCGT posted) vs fiction (the info you copied into your original post). I love the part about 'integrating' the hp curve to get torque, when in fact all it takes is a simple division of hp by 5252 to get the torque curve vs rpm. There is no integration involved.

And, who cares what the car weighs? Totally irrelevant. Power is power, and weight of the vehicle has no bearing on this measure.

 

(again, posting a response to the orginal poster of this information from another forum)
you are on the right track with the mustang dyno, with a few corrections. again, you cant get even a torque value, without knowing the diameter of the tires. however, you can get a tangential force value and a velocity equivalent. (mph) and thus torque at the dyno wheels. with those two components, you can derive power. (power = F x velocity) . or if you use the torque driven on the rollers and know the speed, you can calculate power. If you add in some kind of progressive air resistance or rolling resistance force, well that's just icing on the cake to try and simulate what the car will do in real life, but good luck with accuracy there. too many external factors to consider, butt that's another story.


Now," power is not a force of nature" really??? are you kidding? "cant be directly measured" really??. Power is proportional to acceleration, it determines acceleration at any vehicle speed. means, if you have a force, and you don't know the speed, you have no idea unless you calculate it, how much acceleration that force will have on a car unless you know the car's speed. IF you know the speed and the force (the power), then you can know the acceleration. To show this even more directly, all you need to know is the rate of change of kinetic energy, and you have power. this is just as easy as knowing how fast the rotational speed changed in the drums, and you instantly have power! the UNITS of power are man made, but GOT made power and it is what drives anything in motion in the universe. HP-seconds, is a unit measure of work, its like a KW-hour or -second. HP or "power", is the rate of doing work. it can be measured directly, a number of ways even without a force value.

 

There are vast numbers of people that have run on the different types of dynos and have gotten different results. There are also a lot of tuners that have used more than one kind and gotten different results when doing comparisons of the same car on different dynos.

The theory that they all should work the same is one thing, but real-world results show that more often than not, different dynos will give different power numbers. This is especially true with DynoJet giving higher numbers than Mustang or Dyno Dynamics.

Test after test after test has shown that dyno numbers often do not match to each other.

 

XWCGT - you do realize that's a quote of a post, right? Those aren't my words, just an explanation I found by a tuner that uses dynos.

 

this is not true . by understanding how the dynos work, and making sure things are set up the same, you can get the "same" results for the same car on different dynos. Ive seen this test a bunch of times . contrary to your point, I have posted two same types of cars (aston V8 2007 4.3L) and they have grossly different HP values on the same type of brake dyno. why is that?


the correction factor? maybe that rolling friction/ aerodynamic factor you mentioned? It could be how the test was conducted? engine temps, how it was strapped down. kind of tires on the car, inflation, etc etc.
generally, if all things are controlled, the results will be the same, regardless of the dyno uses. the dyno manufacturers are not dumb, their stuff uses a unit called " Horsepower" and they know how to measure it correctly.


but, the bottomline, there is nothing as pure as the dynojet for actual HP. you cant fool the 6000lb drums which allow the car to very similarly accelerate them at near the same rate as the car would be on the road.
AND, by knowing the mass of the drums and how fast they are accelerated, its a simple calculation of how much power you have.


"heartbreak" usually happens when one side or the other lies.

 

Dynos are women. That's why they can't get their stories straight and can't be trusted!

 

Ah!!! my apologies!! Now, you can start quoting the corrections and fire them back to the internet! let me just say, we are out manned and outgunned by misinformation.
the most famous one, regarding HP and torque was one done by Bruce Augustine. so many errors in his commentary, that I lost track. often used by anyone discussing the subject. incorrect and misleading on the topic.

 

They can tell me any story they want, as long as I can pic the one with the bigger rollers!

 

I'm seriously laughing at that

 

whoever posted this really has it a little backward. the fact that there are some inputs to change the conditions so drastically, makes me doubt many of the mustang dyno results, so I go back to my original thought. always make sure you get the "actual" results of your dyno run, just incase the "adjusted" results are really different.
But, to the OP's point. real life is not the dyno peak HP, its the area under the HP curve over your particular operational RPM range (sometimes called gear spacing).
a quick way to do this, is to take a simple average of the HP at the beginning of any gear RPM, to the RPM at redline. (or a third point incase you have a bell curve at near peak HP). this is the reality check. peaky HP curves will produce less overall acceleration vs a flat HP curve up in the higher RPM. its all HP-seconds. whoever puts more power down to the ground for the longest, will win the race

 

I just dyno'd my car yesterday (06' DB9). Below is the video. 388 rwhp is what is registered at. Anyone with similar for a DB9?