Aurel- Now if you take the car to an actual chassis dyno, then we can see if any of this is right, and if so which one(s).

That would be cool!

Would need to get an accurate car/driver/fuel weight total for the comparison to be valid.

Wonder how running a 23" wheel v 25" wheel would effect the reading?

The onboard iStuff needs all that drive & car weight, but the chassis dyno doesn't. Some dynos don't even need the gearing or tire diameter. The dyno operator will know.

I do not think that on most chassis dynos the operator dose not need the gear ratio or wheel size. It just takes the relationship of the motor rpm rate as taken from the motor lead they attach and dyno roller spin rate. From this, the effective gear ratio can be calculated and allowed for.

The in car dyno needs accurate weight and other info to calculate HP using the cars rate of acceleration.

I do not know if it asks for wheel diameter. On our 911's we see anything from 23" on a 205/50/15 to 25" on a 205/55/16.

I probably won`t spend the money on a real dyno session, unless I have to for tuning purposes. But I encourage others who already have dyno charts and iphones to try for themselves and keep this thread going. So far, we have 202 hp for a NA SC, and 285 hp for a turbo. Seems in the ballpark to me, and there are comparisons with real dynos and dynolicious on other car models that show how accurate it is. Let`s keep the data coming !

How is it obtaining data to perform the calculations? GPS? I imagine with GPS and you telling it everything else (i.e. estimated drivetrain loss, vehicle weight, etc.) it could do it. Is that how it works?

Yes, GPS tells the absolute speed, and the built in accelerometer measures acceleration. All else the software needs to know is vehicle weight and drivetrain loss. I haven`t tried yet to measure hp by accelerating from speed A to speed B (say 45 to 80 mph in third), but I think it can be done too.

I don't think the ipod touch has gps. The accelerometers are used to calculate speed.

My wrong, you are correct: it doesn't have a GPS chip, it uses your WiFi signal and computer to figure out your location. Then, it should not be able to know speed if my initial speed is not zero, right? I`ll try anyways...

The wi fi location feature threw me off as well. I couldn't understand how it knew where I was when there was no GPS! Smart little gadget.

I am pretty sure you need to be stationary to start the test. You will notice there is a delay from when you initiate the acceleration test while it figures out if you are stationary. Then it will start the test.

I have one as well, the problem is on our snow covered roads I can only lay down a whopping 58 rwhp with the traction control kicking in and out on my 330i. Bummer. Need a dry road for it to work.

One other thing to be aware of, there is no correction for altitude, air pressure, temp etc. Essentially no correction for air density. Hopefully future releases will take care of this. This can easily account for a 5-15% error in calculated hp.

All in all a pretty cool toy.

Looking forward t trying the friction circle on the track in the summer.

This video explains the technology Apple developed to find the location with wifi. Pretty cool indeed.
http://www.youtube.com/watch?v=mmoDqPyofok

PocketDyno should be free, I have it and never paid for it.

Dynalicous is supposed to be 0.02 seconds accurate for 1/4 mile and + or - 3 MPH accurate.

I gave it a go in the 911. I didn't have a perfect straight 1/4 mile and the iPhone wasn't secured very well, so it was a little rough. I know a place I can go that is straight and I think it's over a 1/4 mile. I'll post my results later.

I also installed the free PocketDyno app. I'd like to try both at some point.

The numbers I have so far:

weight - 2855 - includes me
loss - 15%
HP - 190

I managed to get 4 runs in today. They are all similar, except the last. I shifted at redline on the first 3 and a bit into redline on the last.

http://forums.pelicanparts.com/uploa...1232414406.jpg

http://forums.pelicanparts.com/uploa...1232414622.jpg

http://forums.pelicanparts.com/uploa...1232414636.jpg

http://forums.pelicanparts.com/uploa...1232414647.jpg

I used 2855 for the weight, should be close, includes my weight.
DTL: 15%
0-60: 7.04, 6.87, 7.38, 6.75
HP: 214, 214, 215, 224

I'm running a SW chip, no cat, Dansk premuffler.

I may try again tomorrow. If the numbers are true, great!

slodave,

Did you get a chance to try the runs with PocketDyno too? Just curious how the free version stacks up...

No, I thought about it, I think I will try a few more runs tomorrow and also try with PocketDyno.

BTW, the HP numbers are from a 23x,xxx mile engine.

I did two more runs today. Dynolicious reported 223 HP and 0-60 in 6.97. I shifted in the redline again, like the last run yesterday. I have yet to get a 1/4 mile time. I need a longer road...

http://forums.pelicanparts.com/uploa...1232504420.jpg

As for PocketDyno... I gave it a run and nothing. It did not stop. The only way to get tit to stop, was to exit the app, loosing the data. I will try some more with my Toyota. Stats won't be impressive, but maybe I can get a few runs that report close numbers.

Question - is it correct that to get an accurate HP reading using Dynolicious (or other G-meter), it is not necessary to brutalize the clutch for the lowest possible 0-60 time?

In other words, a controlled start then full throttle once you are rolling is good enough?

Your results are pretty close to my dyno results with a similar setup.http://forums.pelicanparts.com/uploa...1238021602.jpg

Short answer - yes.

Long answer - The measured HP is the instantaneous maximum measured during the run. A full-throttle start may benefit the 0-60 time but won't affect the measured HP.

Very long answer: Instantaneous power = mass of the vehicle x acceleration x velocity. You program in the mass, the iPhone measures acceleration directly, and measures velocity indirectly by integrating acceleration over time. So the HP it reports is the maximum instantaneous power measured during the run.