Timed real world 0-100 kph time Z4MC

BMWZ4MC

BMWZ4MC

Lifer!
 Diving out of the sun
I bought a P3 Digital Interface from another forum member a while ago but I've not had time to fit it before today. It connects through the OBD II port and acquires information from the ECU. As well as various other data, it displays 0-100 kph times measured entirely automatically. Of course, once fitted I had to test it thoroughly :D

Conditions were clear and dry with an air temperature of around 7 C. The road surface was flat, smooth tarmac and the fuel tank half empty. The time shown is that from 0-100 kph using first and second gear with DSC off, modulating rear wheel slip with my right foot. I didn't rev and dump the clutch, rather pulled away engaging the clutch as one would on a Sunday afternoon drive...just with more gas! I shifted from first to second at around 7800 rpm. The time shown was my third and best run of three.

image_zpsf54c0294.jpg

I knew that the 0-100 kph times were less than the 5 seconds widely quoted, but 4.17 seconds is pretty impressive. On my first run (with DSC switched on) I hit the limiter and managed only 4.7 seconds. During my second run the DSC briefly killed the revs as the tarmac was greasy with salt, so this run yielded 5.7 seconds.

At some stage I'll have to try a 0-60 mph run and see how that figure compares.
 
thats very good, and thats a really neat little unit under your vent. very cool. Does it show coolant temp/ oil temp ?

fastest I've seen on the z4m platform was from a supercharged usa owner with Vbox result of 3.6... sadly his driveshalf snapped on the next attempt :|
 
No doubt the cold air and dry road contributed. I'd love to know what yours could manage...

It's a great unit that looks OEM (even down to the BMW orange display). It shows intake, exhaust and coolant temps, as well as throttle opening, rpm, speed, battery level and probably a few other things I've forgotten. For me, coolant temp is useful for track days to supplement the existing oil temp guage. Comparing intake temperatures with 0-100 times will be interesting too as the weather warms up.
 
That looks awesome. How does it measure the road speed out of interest? Might be worth comparing the speedo's stated speed with gps if it measures from the speedo.
 
I presume it displays speed from the same feed as that used for the speedometer. It seems to correlate with the analogue speedometer although I've yet to exceed around 70 mph with it fitted. I'll see how it fares at higher speeds when I have an opportunity. The analogue speedometer in my ///M is less than 1 mph different from GPS measurements at speeds over 100mph so I suspect it's pretty accurate.
 
Angelus666 said:
That's very cool...How much are they? Did someone say goup buy...?
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Think they are import only

http://www.p3cars.com/bmw-z-series/p3cars-bmw-e85-e86-z4-vent-integrated-digital-interface/

Edit - some UK sites have them but I can't find a z4 version

http://www.vividracing.co.uk/p3cars_H47pc.php?searchtext=rieger%20golf%20r32
 
BMWZ4MC,

does the device record the following:
1. Intake air temperature
2. Mass Airflow
3. RPM
and
4. Speed
all at the same time?

Any chance you can send me any recordings saved as .csv files?

Good effort with the acceleration :thumbsup:
 
Hate to piss on the parade here, but I had a P3 in my old zed and it doesn't start recording straight away I dont think, if the car is rolling before the clutch is engaged then this isn't covered and the car is already rolling.

Obviously if you make sure you are not rolling first and it is a def a standing start then perfect but that is quite difficult. I guess either way it will be relatively accurate.

They are good units though.
 
I think the original owner imported it from the States, I know that it was quite expensive new. A group buy might reduce the cost but might be complicated if you buy direct from the States.

exdos said:
BMWZ4MC,

does the device record the following:
1. Intake air temperature
2. Mass Airflow
3. RPM
and
4. Speed
all at the same time?

Any chance you can send me any recordings saved as .csv files?

Good effort with the acceleration :thumbsup:
Click to expand...

Hi John. I don't think it measures mass airflow but it does the other parameters. I'm also not sure that it is possible to access the data other than in real time. The 0-100 timer starts as soon as the car moves and stops when the car hits 100kph. The time is displayed only until the car comes to a stop when the timer resets for another run. I'll have to explore it more to establish whether data can be stored and later retrieved.

AndrewZ4MC said:
Hate to piss on the parade here, but I had a P3 in my old zed and it doesn't start recording straight away I dont think, if the car is rolling before the clutch is engaged then this isn't covered and the car is already rolling.

Obviously if you make sure you are not rolling first and it is a def a standing start then perfect but that is quite difficult. I guess either way it will be relatively accurate.

They are good units though.
Click to expand...

I'll try to establish what is the trigger for starting the timer. It should be relatively easy - rolling down hill with the clutch disengaged should give an answer. Similarly, I'll try pulling away with the clutch at biting point and not release the pedal. Previously I've observed that the DSC is disabled by slightly depressing the clutch pedal, so there must be switch associated with the pedal.
 
AndrewZ4MC said:
Hate to piss on the parade here, but I had a P3 in my old zed and it doesn't start recording straight away I dont think, if the car is rolling before the clutch is engaged then this isn't covered and the car is already rolling.
.
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There are more inaccuracies to it than that when measuring times via obd2.
First of all you have the speedo inaccuracy. Secondly the obd2 sample time is random and sometimes slow. (the sample rate for obd2 is not a constant!)
There are also some phone apps (torque etc) that can measure this way and sometimes use the acceleration sensor in the phone to measure the point of start. That increases the accuracy a bit (only that difference can sometimes differ a few tenths) but still has the speed inaccuracy and sampletime inaccuracy.

The best way to measure if you want to have accurate/reliable data and still do it on a budget is to use a 10hz gps mouse (a qstarz BT-Q818XT costs about £55 on amazon), and for example an old nokia symbian phone with racechrono software (that is a lap timer, but the symbian version had acceleration tests).
Then you have the quarz accuracy of 10hz sample rate, racechrono has a sample timer build in that checks if the bluetooth connection recieves 10hz, and a gps puts out a speedsample that is accurate within 0.2mph (way more accurate than any obd2 speedo can ever have). So that is a really accurate way to sample time when doing tests, and it can differ up to 0,5 sec in comparison to obd2 sampled times. RAcechrono starts timing automatically when the car starts to move (it reacts on the speed difference between 1 sample and the next)

The reason why a gps mouse can sample speed that accurate is because for speed calculation it doesnt use coordinate data to calculate speed, but it measures doppler effect from the sattelite frequency (which is very very accurate; controlled by an atomic clock inside the sattelite), and because the frequency is very high (total wavelenght is only 20cm!), the doppler effect is very easy and accurate to measure (the sattelite positions are fixed in geo-stationary orbit obviously). Really quite ingenious. The limiting factor is that the fastest sampeling gps mice (and other equipment that is still affordable) can only sample 10hz, so timing is limited to the 0,1sec (but at least accurate within 0,1sec). So it's not really suitable for racing (or sprinting matches etc) which require 0,01 (or sometimes 0,001sec) accuracy.

BMWZ4MC said:
I'll try to establish what is the trigger for starting the timer.
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you cant because the obd2 sampling time (or refresh rate) is not a constant. One moment it can be 0,1sec, and the next 0,5sec. It can even be more than 1 sec.
So it's not only speed related.
The sampletime/refresh rate is not constant because an obd2 port does not 'broadcast' data, but data must first be requested before it's broadcasted. The more requests, the slower the broadcast.
 
BMWZ4MC said:
Hi John. I don't think it measures mass airflow but it does the other parameters. I'm also not sure that it is possible to access the data other than in real time. The 0-100 timer starts as soon as the car moves and stops when the car hits 100kph. The time is displayed only until the car comes to a stop when the timer resets for another run. I'll have to explore it more to establish whether data can be stored and later retrieved.
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Hi Richard,

If you have a link to an owner's manual that'd be interesting. If you can record and save those 4 parameters simultaneously as a file, I've made a database that will give Volumetric Efficiency which I find is the most informative way of assessing the performance and improvements gained from mods.
 
I'll look into it - the existing instructions aren't terribly informative so I'll email the manufacturer :thumbsup:
 
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