Discussion and questions related to the course Practical Standalone Tuning
Hi. Once again, I cannot find any logical explanation of the fact that the same cars always demonstrate more power level when using the Dynojet when Mustang dyno. And everyone seems to accept this as a normal thing. But it is very strange to me as there is only one real physical HP that can exist. At the same time I know that Dynojet is officially used in NASCAR... So how come we've got two systems that show different figures on the same cars? I know Andrei said a few words on that a couple of weeks ago but anyway - can anyone explain?
Chassis Dynos do not measure horsepower, they calculate it from the torque required to accelerate a mass (dynojet), or the load measured by a load cell (Mustang). Because these two brands use a different techniques, you can get two different results with the same car. As long as you stick to the same dyno, results are generally compare-able -- so you can measure the results of modifications, and tune to achieve the maximum torque (and thus horsepower).
Other issues that can affect results even on the same dyno:
-- tire-to-roller traction. This is affected by everything from tire & roller diameter to tire compound, tire pressure and even how worn the roller is. A big factor can be how the car is strapped down. At the recent PRI show, I saw that many of the dyno manufacturers are introducing hub dynos (like the Dynapack, and the Mainline Hub Dyno that HPA has recently acquired). These eliminate the tire and measure the torque directly from the hubs.
-- operating conditions for the vehicle. This is everything from the ambient air temperature, engine oil and coolant temperature and even the the oil temperature in the transmission and rear end. If they aren't the same, you can't expect repeatable results.
Hi David. Thanks a lot for your quick reply. I do understand all what you said and there are no two ways about it. My question was about a little bit different thing- it makes me frustrating that people accept the fact when two different systems show different numbers. I clearly realize that dyno is just a tool to demonstrate changes and if you stick with the same system ( whatever it is) you will see those changes and it is basically all what you need. But at the same time when I look at Mustang dyno numbers I can see that they match the air flow figures (10 hp for 1 lbs as a general number) whilst Dynojet ones do not... Where do you get additional power if you don't have additional air for that?))) I'm just trying to be logical here))
People like to play team sports and brag and Dynojet has played in to. I get people claiming many numbers when they've asked for help, I tend to smile and nod until I put them on my DynaPack, sometimes what's been claimed is accurate (according to MY dyno), but most often not. Sometimes people leave unsatisfied.
Hi David. That is my point. Many people seem to be caring too much about the figure itself rather than actual dynamic and no one cares about theoretical justification. I remember the case when one of the famous drag racing team that holds GTR world record replied to their customer that 350 whp on their Mustang dyno are equal to 400 whp on Dynojet and ET time is identical... I just can't get it))))
People are lame, and so is the internet when they start talking to eachother and their inner keyboard cowboys let let loose. Generally when you start getting face to face folks are of more sound judgement.
Well, the best way to take these is to realize that a dyno is a measure tool to compare an initial condition and a future condition. So is like a caliber, at the end of doesn't matter if number ar bigger or lower in other dyno's, the important thing is to measure in the same one so you can apply your change with confidence.
Also a load cell dyno can be very close to the real number when the cell load is correctly calibrated, the software is well designed and you have a good whether station the gives you the humidity, pressure and temperature. The position of the station also is important. I have seen dynos like Dyno Dynamics, that the operator use the temperature sensor of the interface, and put it next to the exhaust and a Honda Civic of 140hp gives you 250hp... for your photo on Instagram... is sad.
On inertial dyno or a dyno like Dynojet it also depends on the mass factor of the dyno and the calibration, the great part is that you can repeat the test every time and is very consistent. More than a load dyno like Mustang.
We have only like 7 dynos here in Chile, all differents brands. All of them gives you different numbers. Tuners use the one that gives you the biggest numbers and professional racers use the ones that gives you consistent and repetitive values. Specially inertial dynos where you can work with the power drag of lubricants, alignment, indictions and other mechanical factors that need the precision of 2 or less HP. The reason is because the work all year on the development of the cars and needs a tool that can gives them a confident reading, it doesn't matter if is 10hp more or less soon as is a repetitive value.
At the end there is the sentence: "HP sells cars but Torque win races"