But regardless of clams, No Post Allowed - nobody can post anything about their unsubstantiated accuracy claim.

General banter about different dynos and that dj's read higher than other dynos.
Nobody had figured out that the dj inflation factor % increases as power increases
We write our own tuning software and I can agree that some other dyno software is onerous to use for tuning - even though the dyno works well. In my experience, complicated software can make the dyno unusable for some non-savvy dyno owners. Our EC997 dynos allow the choice of Sweep or Steady State testing. Even THAT choice was too complex for one of our early customers, a Los Angeles guy.

Natively, the Mustang dynos read lower than the dynojet, as they don't natively exaggerate the power numbers
What I don't like about some dynos, is that in a Sweep Test, people can diddle with the "inertial mass" of the dyno and fudge the numbers up.
We promote quick Steady State testing for HP numbers on the EC997 - there is no adjustable "inertial mass" factor in a Steady State Test to fudge numbers.
What we do in a Sweep Test, is to do a Steady State Test for True HP values, then a Sweep Test, then take the Sweep Test results and adjust the "inertial mass" value until the Sweep Test HP = the True Steady State HP.
Pretty logical.

I was kinda surprised to see what I wrote on somebody else's website - But, I guess, if it gets plagiarized, I guess the guy thought it was right.......

At the end of the page is a guy who went to 4 different dynos with the dj dyno being higher than most. What is interesting, is that there's a Mustang dyno that read about the same as a dynojet, but, al the other dynos read lower. On other links, the Mustang has the reputation of reading the lowest.
Because the Mustang software, in a Sweep Test, allows fiddling with inertial mass, the dyno owner may have bumped the value up to make his Mustang read higher - so, any HP readings from that dyno are useless when comparing power to another car on another dyno, even a dynojet or another Mustang.

A pretty good explanation of a lot of dyno things -
Motorcycle tuning is usually done to a higher level than car tuning - as a 2% HP improvement makes a difference and in the motorcycle industry, while 90% of dynojet, tuning to an AFR and their "Sweep Test and tune to an AFR clones", still has a decent percentage of people who have advanced beyond tuning to some mythical optimal "AFR" and, instead, use power, engine smoothness and fully integrated multigas EGA's to help tuning to "engine optimum.
The difference between "tuned to an AFR" and :"tuned to where the engine runs the best" results in better real world power, smoother and cleaner running and better mileage.

Dynojet Inaccurate.htm
3 different dj dynos, 3 different sets of hp numbers, national magazine reprint

A statement about how it's known that the dj's read high.
Also- the poor guy made some changes to his car AND went to a lower reading dyno. A clue that "all was not right'  with the car is that it bogged at 4500...... To add to that thread, ANY car should be able to run WELL at full throttle, under most any realistic load condition.
Look at it this way, as far as dyno load vs real world load.
The MOST load you can have is pulling a trailer up a hill at full throttle, where the engine can't acc. That NEEDS to be tuned correctly, so, a dyno test SHOULD include that load condition (that's called Steady State, that experienced dyno tuners talk about).
Unsavvy tuners think that whacking the throttle on and doing an inertial Sweep Test and blindly tuning to so "AFR" is optimal? It's not.
There was a company that was enamored with their new, so-called "state of the art", big wheel / AFR dyno. Their product, Mustang car superchargers, made great power on their new "self proclaimed State of the Art" dyno - but, bogged and pinged in the real world. My FL dyno tuner buddy, gets a call to help with the tuning. Yep - AFR's right and ign timing is right on the "dyno". Yep, in the real world, where the loading is greater, ping and bog. So, PR sits in the car with his laptop and one of the dyno owner guys drive around FL and PR fiddles with the fuel and ignition until the car rips in the real world.
They take it back to the big wheel AFR dyno. Crummy HP and totally "wrong" "AFR" - That's what we call a "Reality Clash". The inertia big wheel AFR dyno was totally wrong..
 How many people are driving around with lost power?

I'd have to be in a pretty bad mood and the guy I was talking to would have to be pretty annoying to call something "c**p"....  but, if I did, you could read Winders' post and maybe see why.
Bad thing about the internet, even if you learn more in the last 6-7 years, whatever you said back then stays there.....
Micty's post about calculating power using drag coefficient, frontal area, rolling resistance and velocity on a NON-RAM AIR bike is excellent.
We've done that and, pretty much ended up with what we call True HP on an EC997 and about 10% to 15% less than a dj hp number.
In fact, the BEST way (but not the most convenient) to measure power is in the real world. For example, making a tuning change at the drag strip and picking up .2 mph means that you've improved power. What we've found over the last 30+ years, is that a Steady State dyno test is ~98% equal to the real world as compared to a 4th gear, 10 second Sweep Test, which is less equal to real world load conditions. At least that's the way that Michael Jordan (2005-2012) Racing feels - and, to correct a post in that thread, FUSA used a Factory Pro EC997 dyno, after they used a dj dyno and the Canadian HP limited class uses a dj dyno, maybe because Parts Unltd, the dj importer, is the long time sponsor of the Canadian Series.....

I'm not any one of those guys with the "c**p" comments. <wink!>

Why DJ power aren't True HP and a logic path..

Discussion "Rear Wheel Horsepower" "SAE", EC997 dynos, dynojets and "common dealership" dyno inaccuracy (that might explain partially why CCS switched from dj and so on).

Ok - this magazine test stretches credibility so far, that, well.... it's, well, that word that's 4 letters,  starts with c, ends with p and has an r and an a in it. <wink!>
If they didn't start off with an inflated hp number, the car wouldn't have to be ~90% (impossible in a normal car) in the drive train power transfer efficiency to make the manufacturer's claimed crank HP.

The scary part of this page is that you have someone saying he's a dj rep saying that there's a potential dyno tuning error if the car weighs more or less than 3200 lb dj drive roller, that the tuning results might be in error (the MINOR point!) - then another guy who says that he has the 4200 lb dj drive roller and thinks that's "right" for a 4200 lb car. And that post stood without correction.

What's scary about that is that the dj guy is or was an engineer at Ford?
It makes little difference about the actual weight of the driver roller, it's the Inertial mass - NOT the weight.
Example: If you put a 3200 lb 1' bar on frictionless bearings, you could turn it with your hands, Very low inertial mass, but, it's still 3200 lbs.
Build a 3200 lb, 24 ft diameter, heavy rimmed flywheel, and I'll bet, you'll have a pretty hard time accelerating it, even with all of your weight.
Remember, it's the LMR (Linear Mass Rating), not the weight.
I am guessing that 3200 lb dj drive roller is more like 1500-1700 lbs of Linear Mass Rating.
So - the load applied would in simplest terms, be about right for a 1700 lb car (even ignoring real world 1/2 rolling tire resistance and wind resistance)., not a 3200 lb car.
The MC dj dynos drive roller, weighing about 900 lbs, has about a 425 to 430 lbs "Linear Mass  Rating". according to an ex dj employee.

The funniest exchange that I heard about the dj auto "big wheel" 1700 # LMR driver roller.....
"Well, you know that the roller is only equivalent to 1700# of mass, right - so how can it properly load the car??
"Yeah, I know, but, it's still right."
"Huh? How's that??"
"The car weighs about 3400# and I'm only dynoing with 2 wheels.......1700# is right."
<emoticon of little guy shooting self in head>

How Dynos Work - A few years old, but, explains the difference between your, still normal, dj inertia Sweep Power Test (how they measure power) and an EC997 loaded Steady State test and information about True HP vs, DJ HP.

EC997 Factory Pro FUSA Official dyno

Andy Marcer, a well respected tuner in Houston. Metric Motorcycles - He loves his dyno.

Long discussion about that 25 year old guy you met in a bar who drove a 500  hp Hayabusa as a daily commuter and used to drag race for Yoshimura and was National Champion. He also had a 40 djhp 125.

A long discussion, about True HP and how it relates to djhp. In the thread, the "other guy" argues that the "old 150" dynojets read too high, but, the 250i hp is "fixed". So, that was 2007.... and we all know that the numbers that different dj 250i's are almost always 10% to 15% higher than True HP, depending on the dj dyno.
Note: As of Aug 09, "power" is normally measured on a dynojet in an inertial sweep test - not a brake loaded test, as in EC997 dynos.

Yes, much as I try to ignore it - EC997 dynos DO have a method to inflate HP numbers to something "around" a dynojet hp figure - It's called a "Quick Sweep" test and I actually forget it's there.
It is NOT called dynojet emulation or dynojet math channel, it's a totally different loaded sweep test and it must have some same software assumptions/errors of a dynojet inertia power test = it sweeps slightly too quickly (attempting to get a dj shape of power curve) and it has a "fixed" bike rotating inertial mass (ie, having the software making the wrong assumption that a Fat Boy HD has the same rotating mass as a yz250), to try to get the same power value errors as dj's sweep test.
The, always present problem, is that, unless you do you dyno loads with a 900#/430 LMR rated driver roller, you never get exactly the same shape of the power curve (and we are ignoring the djhp inflation factor).
Some Centers use the Quick Sweep on "Dyno Days" and some new dyno centers initially use the Quick Sweep for their initial customers and till the local riders get used to saying "true" and djhp" to qualify their hp numbers.
In Marin and northern CA, there's 4 EC997's around here and most street riders, even HD guys are used to True HP numbers. It's pleasing to tell a HD guy that he's got "85 True" out of his 103 and he says "Great, that's what I was hoping for.".

There are some great people on the internet. One of them used to fly, well, I can't tell you what or where he flew, but, now,  he might be flying you across the country...... and Tim Radley is a well respected tuner and a decent guy. Had great conversations with both of them.