I hear the other side of the arguement.

Repeating the same # is KEY. They dyno has to be calibrated, that would defeat the whole purpose. Now tuners use DD to put in there own altitude, humidity etc is dishonest. Not dyno's fault but user's. I guess you can say the DJ is more reliable and better calibrated b/c of that. I presonally use DJs (at vette doctors or mustang magic) but for my brothers awd car we used a DD (th shop ct).

 

DJ in inertia mode has no calibration. There isn't one needed. As opposed to the DD calibration which only consist of zeroing the load cells. Anyone who has ever worked with strain gauges or load cells will tell you how sensitive they are to drift and temperature. To properly calibrate a strain gauge you must zero it and you must calibrate it at some load and hope the sensor is acting linearly. A good measurements guy will do a piecewise with a strain gauge as he uses it... Zeroing it only is a joke IMHO

 

Further, anyone who owns a DJ will tell you how consistant they are. We had a nitrous car recently with a fuel issue. We ran the car on 3 different days over the course of aout a month and a half. The car dynoed +/- 3rwhp NA no ****.

 

I think there's a problem with semantics here. The mustang dyno doesn't use a "factor" for different vehicles. It uses actual, quantifiable information which is weight and drag information. This doesn't allow you to "create" an overall power number but it allows you to properly tune the given vehicle. If you have an LS1 in a miata and a GTO which is going to put more load on the engine?
Now they may output the same rwhp number if they have the same tune and all but wouldn't you be able to tune the miata LS1 more aggressively since you're moving less weight, less load?
As far as repeateability, where's the proof to show non dynojet dynos aren't repeatable?
My Mustang Dyno is a closed loop, feedback system that allows me to graph the torque the rollers are feeling from the car, the voltage applied to the pau, and the amount of resistance created. All in quantifiable units, so yes I can verify the repeatability. I don't fudge numbers, there's no reason to and I can prove all of that with the method I just stated. You guys keep talking about fudging numbers, so read the article I posted early, it's right there in black and white. It's public proof that there are "factors" built into the dynojet yet you guys keep referring to them as giving "realistic numbers." Who's kidding who here? Frankly I find it funny how a bunch of tuners are so hung up on final power numbers. Who cares if the dyno says you make 100 rwhp, it's about how the car performs at the track.

 

Im going to agree wit Alvin on this one. As a customer you always have an idea of what your car should make and if it is way low then you will think you have a problem an start chasing a false problem. I understand the dyno is just a tuning tool but it has to be in the ballpark.

 

I almost want to get some sponsorship to have my car shipped to Katech and get them to yank the motor, do an engine dyno, and then put it all back together - and have my car shipped around the country from tuner to tuner so they all can do 3 back to back dyno runs and lets get a baseline once and for all of what a known engine dyno number setup does on the various rolling road dynos of the different tuners.

Then we correlate all the info and publish a "Tuner Correction Table" to stop all the bullsh!t once and for all

hehe - now where did I put DynoJets phone number... ??

 

If you are tuning partial throttle for a truck that's going to be hauling a load, you bet it matters. Drivability tuning will be different for a 6000 lb truck hauling a 5000 lb trailer, versus having the same motor in a 3000 lb car. Sometimes tuning isn't all about 3 WOT pulls and you're done, there's your number, pay my tuning fee please...

 

I'm with everyone else on this one, Alvin. The Dyno Dynamics are fantastic. They're very repeatable and consistent. Awesome for tuning too. They do show a lower number, but the gain is what counts. Did the customer think there was something wrong with the gains you made while tuning?

 

Why does everybody think tuners are wrapped up on final #'s ? It's always the customer upset when a low reading dyno graph is given to them.For myself and the racers I tune for it's about track #'s but the other 90% of the people just live off a dyno sheet.If we got a dyno that reads alot lower I GARRENTY we will lose bussiness.

 

Thats a bit different of a load than a car. And BTW, I'm not a 3 pulls and we're done kinda tuner. Anyone that I've tuned will tell you that.
I can apply a pretty decent load on my DJ. If you dont own one, then you probably dont know how.
If you wanna discuss methods of loading an inertia dyno, maybe we can start another thread.

 

As a customer I have had my car on a mustang and a dj, ultimatly I picked the dj shop as my place to tune. IMO you should pick a shop and stick with it so you don't run into issue's with numbers bouncing all over the place.

 

Ignore the numbers, every dyno guesses the flywheel horsepower (which they call Rear Wheel numbers), none actually measure the true power and/or torque. You really think 395 rwtq is going to move a 4000lbs dead weight? I don't think so! Dyno numbers are just what the dyno manufacturers uses to calculate power, either by estimating the horsepower like dynojets and back calculating torque (rpm signal) or actually measuring true rear wheel torque like a dynapack. Dynojets numbers can be altered by how you strap the car down on the rollers or by using light weight wheels/tires. As for your analogy of the weight scale, say you always weighed your self on a Wal-Mart brand scale for years, and you know your weight and believe you are healthy. But one day you need to see the doctor, opps! You weigh more then you though and are not as healthy. Now the doctor has you on a strict diet to loose weight. Why, the doctor uses a more precise scale, rather then the cheap brand that Wal-Mart imports from taiwan to sell for cheap. Just because you have always used a certain dyno for numbers, doesn't mean those are the correct numbers. If you want correct numbers, you need the vehicle weight and the trap speed over a set distance, period!

Summary:
You want to make sales, use the highest number outputing dyno.
You want to calibrate vehicles, concentrate on the gain from the baseline number, regardless of dyno used or use the track exclusively.

 

so you think every dyno guesses what the fly wheel horsepower is instead of what the RWHP is huh? I dont think you are even close on that one.

 

I've never seen much of a difference from strappin em down differently on the drum. You're not gonna make a 400 rwhp car 420 by changing the way its strapped down.

I've never seen a scale, even the cheapest ones, that was off 10 or 20 %.

What about the people that cant drive? Theres more variables in drag racing than in a repeatable piece of equipment.
As for shear numbers, end results, whatever, I could care less if my dyno reads high or low. I use it to quantify changes.
We dont cheat the weather station. We dont use saver spares on the backs of cars. But its repeatable, and you cant enter stuff into it to skew the data. Thats all I need.
And with the widely varied results from other name brand dynos, I question ALL the results from them, unfortunately some unjustly.

 

Do you really think that 400rwtq is going to push your car that weighs 3500lbs down the 1/4 at about 11.9 @ 113mph? The rwtq numbers we see constantly displayed by various dynos is false! That is the figure after the drivershaft, before the differential gears. But since we do not know the actual drivetrain loss after the clutch/converter and trans, we can only guess that figure. The differential gears will multiply that flywheel torque figure from 400fwhp (assuming no loss) to 1368rwtq when using 3.42 gears. Also if you start in first gear for a T56, you need to multiply that figure again by 2.66, which is now 3640lb/ft of torque. This is why lower gears (higher numerically) feels quicker then higher gears (lower numercially), and why 1st gear will out accelerate 4th gear in any transmission. Is it clear now?
That is because you are not like other shops I have visited that have figured out methods of manipulating dyno figures. I have seen it on many dynos, and as you mention (but) on ALL dyno the variables can be skewed.
So a 200lbs person can be either 180 or 220, big difference there!
And this is where most reputable tuners agree, only the gain really matters, not the end results/numbers.

As for driver error in true numbers, I never said from a stand still, I said over a set distance. Elapsed Times are driver and setup dependant, MPH rules out driver errors.

 

Anyone ever notice that EFI-University is taught on everything but DynoJets?

 

everytime a dyno result is posted up by a DD, mustang, dynapack, and now including this thread. you go out with you crap about the correction factor ,and this and that. yeah you are right i can skew my numbers to make a 200 whp car make 500+ whp, but **** if you try you could do the same with a dynojet, blow a heat gun on the weather station, or whatever. you say its dishonest to skew numbers, well you are right! but if that shop that wants to do that, they will figure out how to do it, in either a DJ, mustang, DD, it doesnt matter. as far as tuning, i dont care how many tricks you have learned on your 248, i can do that, and 10X more on my DD. you seriously need to get your head out of your *** about dyno numbers, and worry about the tuning aspect.

 

Mad props to you too Ryne.
I never said anything about dyno numbers being important. On the contrary if you read my post.
As for your DD, I do like them as a tuning tool. They do load better than a DJ. Never said they didnt. What I said was, if you didnt read it, was that I can load mine pretty well, and do some things with it that alot of people say you cant.
On the printout that every one of my customers gets, is the correction factor, and the weather report. If someone is here on a 50 deg day, and gets a printout that says it 90 deg, dont you think that would make them wonder?
The whole point Alvin, and me for that matter is making, is why even give the ability to the end user to be able to change the numbers, just by pushing some buttons?
And yes, your numbers may be legit, but whose to say the guy down the street with the same dyno is?
PS, as far as tuning, theres some customers that come to me that arent worried about numbers. They've been tuned previously and are perfectly happy with their numbers. A large percentage of the tuning I do is driveability related.
Thanks for your concern though.............

 

Thats the whole point right there. And no, I don't think you can do that on a DJ, even if you tried.
I shouldn't have to say any more. You've said enough.

 

you dont think it can be done with a dynojet?? so if you were to put a high amount of heat to the weather station, it wouldnt adjust the correction factor?