More exact vehicle speed logging

Post your feature requests here.

More exact vehicle speed logging

by mituc » November 5th, 2019, 9:59 am

I'd like to know if it's possible to add one or even two decimals to the speed PID, if it is reported properly through the OBD bus.

Especially when logging in mph (which is 1.6x kmph) we see no increase in the vehicle speed when we start accelerating while the RPM (which given it nature is more accurately reported from a time relation standpoint) is increasing. Because of this the speed/RPM correlation is broken which leads to weird curves in torque/power analizing software such as VirtualDyno which may trick us into thinking we have clutch or wheel slip.
2008 Cosmic Blue Mazda 3MPS
Build engine + WMI + GTX3071, ~476WHP @31-32PSI
2008 Icy Blue Mazda CX7
Stock engine, intake and exhaust (YES!!), GTX2867 gen2 + Autotech HPFP, self-tuned to 320-ish BHP
VersaTuner guru
 
Posts: 856
Joined: December 17th, 2011, 2:47 pm
Location: Iasi/Romania

Re: More exact vehicle speed logging

by Ugnius @ VersaTune » November 6th, 2019, 6:38 am

The ECU returns vehicle speed as a single byte with 256 different values from 0 to 255, which corresponds to the speed in km/h. As a result, we cannot increase the accuracy of that.
The speed is calculated by the ABS control module and passed on to the ECU. The speed signal is filtered, that's why there is always a delay between the actual speed and reported speed. As far as I know, Virtual Dyno software doesn't use speed measurements at all. It calculates the speed from RPM and the gear ratio.
User avatar
Lead developer
 
Posts: 370
Joined: March 19th, 2010, 11:57 am

Re: More exact vehicle speed logging

by JohnnyT » November 14th, 2019, 9:19 am

Image

He is asking because he has been helping me with the tune and I keep seeing this in all my logs.
Attachments
4thGearWOT11-5-2019.csv
(14.91 KiB) Downloaded 4 times
VersaTuned - 07 Mazdaspeed3 - CPE Stg2 Pistons, Manley HBeams,Kozmic DP, CNT CatBack, PTE 5862 JB Turbo, DTP Fab Dump, CPE PTE Ex Mani, JMF PI IM, CS 3.5Bar, MAC EBCS, HTP 4" Intake, Trubo XS FMIC
 
Posts: 21
Joined: July 6th, 2017, 4:18 pm

Re: More exact vehicle speed logging

by mituc » November 14th, 2019, 6:20 pm

Indeed, and we can't figure what's that abrupt line right before 3k and then after 4k rpm... and we don't want to make assumptions. It may look like a bit of clutch slip right between those RPM points or just something VD would react to form the logs, as the RPM/speed is kind of smooth, and so is the RPM and speed curve.
However sometimes RPM increases by 25-ish RPM between each line, sometimes by 50-ish RPM and that may cause it.
2008 Cosmic Blue Mazda 3MPS
Build engine + WMI + GTX3071, ~476WHP @31-32PSI
2008 Icy Blue Mazda CX7
Stock engine, intake and exhaust (YES!!), GTX2867 gen2 + Autotech HPFP, self-tuned to 320-ish BHP
VersaTuner guru
 
Posts: 856
Joined: December 17th, 2011, 2:47 pm
Location: Iasi/Romania


Who is online
Users browsing this forum: No registered users and 1 guest
cron