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      10-11-2011, 01:04 PM   #32

Drives: 57' Isetta
Join Date: Oct 2011
Location: Baltimore

iTrader: (0)

I felt it pertinent to add a few notes regarding dyno charts, and dyno's in general.

Being a Mustang Dyno center, (at cp-e) I'm often faced with the "your dyno must be broken" comment, at least once a week. Part of the thing to remember about Mustang Dyno's is that they operate in a completely different fashion than Dynojet Dyno's do.

Note: I am not going to condone any type of dyno X is better than dyno Z talk.

Dynojet's generally use a few simple physics calculations to derive HP,

Force = Mass * Accel
Work = Force * Distance
Power = Work * Time

So, basically dynojet HP is calculated based on a number of factors, rpm, wheel speed, and time (among a few other standards and atmospheric inputs). They use very sensitive optical pickups on the rollers to do this.

Mustang's actually measure torque, in real time. There is the equivalent of a torque wrench on the end of the rollers that is used to measure real time torque. Why is this useful? This is indescribably awesome when tuning cars, due to the fact you can do steady state loading at a specific RPM / load (which the dyno will prevent you going past) and adjust timing or fueling to see if the torque increases or decreases. MD's are a great tool, beyond it's myriad of other cool features (that I won't waste your time talking about, )

Which brings me to my next point, dyno's shouldn't ideally be used for absolute measurements. Example, "Well, the 1M made 366 WTQ on the insideline blog review so your dyno is broken because it only made 320 WTQ on your dyno"

Dynamometers are used as tools to identify changes in the HP and TQ curves at that dyno session, that day. There are a number of different factors that play in to the amount of power an engine can make, measurement strategy that dyno X uses, atmospheric conditions / elevation, humidity, temperature, etc...

All dyno's (that I've used, MD, dynojet, mainline, dyno dynamics, dynapak) have atmospheric calculations, based on humidity, temperature, and atmospheric pressure, but again, they are only really to keep standardization and consistency on that dyno, on that day.

As an example, the insideline 1M test yielded 366 WTQ, and 331 WHP.

Our 1M, made 322 WTQ and 295 WHP. These were both dead stock cars, FYI.

If you wanted to come up with an imaginary correction factor between our two dynos (which is pointless, but someone will likely ask anyway), you could divide the TQ and HP from both charts and find a percentage difference. It works out to be around 10-15 % less on the MD.

Also a note on scaling, The dynojet graph pictured above (a few posts up) is scaled from 0-500 hp / tq. It looks nice and smooth. While the graphs from Steve's car look somewhat lumpy and odd. While I do suspect there was some wandering boost pressure there (as the tq curve does wavier a bit), they are much smoother looking if you rescale the chart from 0-400 hp / tq.

And then...on top of all of the dyno comparisons, you've got the variability of piggyback controllers, conditioning signals to the DME in the first place. Most of the ones on the market do a pretty great job, but the real solution in my mind for the N54 / N55 people is a proper standalone computer. (sander...patiently awaits...)

Apologies if that was long winded, or slightly off topic at times. Hopefully someone got something out of it.

-Sander (guy with hat in first picture)