This is in reguards to this thread..

https://www.evolutionm.net/forums/ev...s-dynojet.html

ME: Tuner at Secret Services Auto.

Theres a few things to look at here.. First yes mustang dyno numbers can be manipulated. We used to have ours setup to mimic dynojet numbers so customers wouldn't complain when their numbers were lower than their buddy. We finally got to a point where I said screw that and set the calibration as it should be.. This was about a year ago.

Now first off, the rest of the dynos in the world don't read low.. Dynojets and Dynapacks read high.. If you search online there is an article where dynojet admitted to fudging the formula and their dynos have read higher ever since. but since dynojet was the only chassis dyno available for so long their nunbers became the recognised standard up till recently.. Dynapacks read high because of the removal of inertial loading (tires) but they are very good dynos.

Now you also have to look at how these different dynos measure power.

Dynojets have a fixed weight (roller) and it measures how fast you accelerate the roller. Take the basic acceleration over time formula and fudge it slightly and walahh you have dynojet numbers. The problem with this is that your car weighs a heck of alot more than the 1500lbs roller of a dynojet, so the amount of load on the vehicle doesn't even come close to real world loading.. Now on a MAF based vehicle this isn't quite as much of an issue, but on a Speed Density vehicle this can be a huge problem. If you tune a SD system to say 11.50 AFRs on a 1500LBS (light load) then go out on the street with your 3200LBS car, you will most likely end up with VERY different AFRs on the street. Depending on what gear you tune in the differences can go either direction.

Mustang Dynos on the other hand measure power in a totally different way. They actually have a strain guage on the eddy brake that measures actuall torque, then HP is calculated from TQ, which if you look at the formula for measuring HP its TQ over time / 5252 or whatever. So it makes common sence as to which one is going to be more acurate. This does a few things. First you can dyno in any gear and the power will be darn near exacly the same, and now you can apply extra load to the vehicle to simulate the weight of the car without affecting the power reading because your measuring TQ and not rate of acceleration.

Now the unique thing about the mustang dyno is that it does closely simulate actuall driving loads. You input the weight of the vehicle and the drag coeficient (power@50) and it will load the car very very much like it will see on the street. Now without weighing the car its hard to say exactly how much it actually weighs but they give you a huge file that has the weights and drag coeficient of every car ever made. The DC numbers are provided by the vehicle manufacturers and include rolling road resistance, frictional losses due to drivetrain, and wind resistance.. So as you go faster the load increases just like it would on the street.. Now while this is not perfect, it is darn closer than any other dyno to actual real world load. The other thing that having a loading dyno really affects is when you have a large laggy turbo. I've had a couple instances tuning on dynojets where the thing would accelerate so quickly that you'd be done with the pull before the turbo spooled all the way, or the TQ would be low cause the pull was so fast that the power came on later in the RPMs.. With a good proper loading dyno you will have very very close to real world trends in Boost vs RPM..

Now mustang dyno makes dynos for all kinds of stuff, they make emmisions dynos, dynos for the car manufaturers, for government, for military, their software and hardware is basically Military spec.. So that being said, IF the operator knows and understands how to setup and use the dyno, perform the regular maintenance and calibration checks and or adjustments, these dynos are probably some of the closest to actuall power you will get. I check the calibration on the torque cell twice a month, and in 3 years I've only had to actually re calibrate it once, and that was when we moved it from the old shop to the new shop. The crappy thing is that yes you can change roller weights and TQ arm lengths and modify the weather station correction factor to boost your numbers, and I know of a shop here locally that was doing that for a while.. Anyways thats another story.

It basically boils down to like what other people were saying. its a tool for tuning, it tells you where you start and where you finnish.. If you gain 50HP over stock its still 50HP weather its 350-400, or 400-450.. This whole X amount of HP = this MPH is not a good indicator of power either. I tuned a car for a friend that made 305HP.. He drove it to a total of 113MPH at the track AVG out his 3 passes. I drove it to 119MPH on my 3 pass AVG, same night, same track.. the power didn't change. I have a customer with a DSM thats making 675HP on our dyno, the dude can't break over a 11.3@ 131MPH.. I garuntee you if I drove that car it'd probably run closer to 140-145MPH.. MPH and ET can vary just as much as dynos..

The DLL/VD deals are cool for street tuning and seeing changes in power, if you can do it consistantly on the same strech or road with consistant driving.. But again it should just be used as a reference from before to after.

I hope this ansers some questions and doesn't get deleted.

 

My problem with the whole "loading a car" issue with a mustang dyno is that loading a car has NOTHING to do with its power output. If it doesnt have enough load on a dynojet then dyno in a higher gear. An AWD car on an AWD dyno jet has two 1500lb rollers and then it is very close to the weight of a car. A car makes the same power whether it weighs 700lbs or 7000lbs. I can tell you though a 7000lb car will spool faster in 1st gear than a 700lb car because the car cant accelerate fast enough before hitting full boost. This is why you make sure to dyno in a proper gear to load the car on any dyno. Tune the car for all load and rpm points so that when you are spooling slow in 1st or 2nd gear on the street your tune isnt off. If you only tune for high loads it is just as bad as tuning for low loads. Know how to use the dyno you are on.

As far as accuracy is concerned hp is a formula, that can be derived from any variation of the formula given the correct info. If you have power you can figure out tq. If you have tq you can figure HP. The problem with the new "lower" reading dynos is the fact that if you do the math from know variables the math doesnt add up. The creator of the dynojet realized this and just couldnt figure out why the drum calculations with his formula werent accurate to what the power should be according to the math so he made a constant to make the numbers correct. He didnt arbitarily pick some #, he scaled it to be what the forumulas that are LAWS of PHYSICS say it should be. Thats why dynojet numbers work so well with hp calculators from the track. Computech does much the same and is almost always correct with the engine dynos and what the cars run. It isnt guessing, it is fact. Mustangs are wrong, they are too low. There is no way a stock evo with 190whp will run 105-107mph in the 1/4mile. Do the math and you will see what is closer to real world.

http://www.fastcoolcars.com/hp_calculator.htm

 

But with more load or less load your optimal timing and fueling requirements change. That is number 1 reason why a loading dyno is better. 2 1500 lbs rollers don't take into account drag and other parasitic losses as speed increases. And dynojet didn't "scaled it to be what the forumulas that are LAWS of PHYSICS say it should be" he made it = what the manufacturers stated crank HP for a motorcycle was, plus adding a little drive train loss. Hardly a benchmark for acurate numbers. Track mph and et CAN be a good measure of power, but realistically it can also be just as variable as one dyno to the next from one driver to the next.. And if you look around at alot of the higher end shops, alot of them are getting mustang dynos or dynapacks now adays. The tunes just come out way more consistant from roller to track/street on a proper loading dyno.. I think the issue is some people just get upset when they don't see a number cause it hurts the ego. No chassis dyno is perfect but the mustang in my opinion is much better tool for tuning..

I'm not gonna argue about math, that can become a very complex topic if you really want to take into account ALL the variables present between the crank and the ground. The math is probably a good ball park and since everyone uses the same "Basic" formulas it does add up most of the time.

Anyways people will make their own conclusions, I just wanted to put this out there since I tune cars every day of the week and have used most of the popular dynos. We chose to buy the mustang dyno despite it reading low because I felt that it was the best tool for the job. In the end the quality of the tune is more important than big #s.. If you want a big number just multiply your power times 1.12 .. That'll give you your dynojet equivalence as I call it.