Performance logging with VCDS

A5/S5/RS5
#1

Guys, looking for insight on what you think the most important parameters are for logging with the VCDS when making acceleration runs on a naturally aspirated car. I’d be looking for anomalies as well as areas for more potential where the ECU may be throttling things back due to running into an adaptation situation (too much torque for instance). There are so many choices and I can only log eight at a time, grouped together in “turbo” mode.

There are some obvious ones like IAT, EGT temps, 02 wideband feedback, rpm, etc…but there are load value menus, engine torque, all kinds of things. Car has no issues and I’m not modded enough to care about fuel parameters.

And then I’d like to have a better understanding of the S-Tronic functions and what to monitor to spot potential weak spots performance wise or where the TCU might be intervening and not allowing full power during a run or when I abruptly transition to WOT or when the hydraulics aren’t clamping down on the clutch quickly enough (and why).

I just want to have a better understanding of which parameters to log and why. There are a metric ton of choices.

Also, is there any way to log TCU and ECU at the same time? Doesn’t appear I can log some engine parameters and some transmission parameters at the same time.

Lastly, is there a better logging option than VCDS? I’m using MegaLog viewer to analyze. It’s cheap and can graph things easily without having to deal with Excel.

Thanks in advance!

#2

So you can’t log the ECU and DSG at the same time. Not with VCDS anyways.

IAT is good just to gauge for one pull after that you can usually do the math on how the car will react. On average the IAT should drop as you accelerate. EGTs ehhh again a good once over but not too needed on average days for logging.

lambda value
total ignition value
total correction - expect correction at peak Tq and some tip in situations
Calulated TQ and actual TQ. I don’t know if you have requsted TQ but that would be helpful as well.

For advanced fun you can do pulls and then log the camshaft output angle

The DSG you can log any and all of the TQ tables. Max alloted TQ . Then TQ request. Pump pressures are always helpful. If you have a tip in situation where you feel the car nose over for a second you can generally trace that back to the clutches building pressure.

VCDS is a great tool. as long as you can output the data into excel and then inport into graphs its good data to be able to view in a range of different patterns. Just make sure if you spot something you put a marker into the log. Otherwise you won’t quite know when what happened when.

#3

I’ll try those. I have been doing ignition correction values and I have logged some of the torque values in the transmission section as well as adjusted cam angle but didn’t find the last one very useful. I’ll have to go look at the exact options as there are many and I’m not sure 100% which ones correlate to your list. While I agree it’s a powerful tool, it’d be super helpful to log more than eight parameters at a time, grouped, in turbo mode, and from multiple sources like engine and transmission parameters at the same time. And it’d be great to not have to be plugged in, car ignition on, to set up various logging parameters and save them for future use.

I avoid Excel like the plague. The Megalog viewer is far more sophisticated and it imports the data and graphs it automatically. You can even graph it in a three dimensional plot. All kinds of good stuff. And the best part, no Microsoft. https://www.efianalytics.com/MegaLogViewerHD/

These are what the 2D graphs look like but they’re configurable in both color and what variables are graphed via a pull-down menu. Pretty slick. And you can scale them in or out to give you as much detail visually as you want or pan back out to see the entire log at once.

https://i.postimg.cc/KvnCr3B6/EGT-AFR.jpg


https://i.postimg.cc/sDcwgYpg/IAT-AIR-MASS-01.jpg

#4

Here are the logs from my drag run posted in the other thread. There’s about a 1500rpm drop between when I engage launch mode and the engine begins to accelerate. The car is moving during this time so that’s probably costing me half a second. Traction control is all the way off. Maybe more air pressure is needed. The Michelins are grippy!

First contains rpm (white), EGT (green) and air intake temps (red). The first big rpm hump is the car in launch mode, second big hump is the shift from 1st to 2nd, etc…

Second graph contains two graphs, the top is the same as above and the bottom logs engine torque (white), load value unrestricted commanded value (green) and load value corrected specified value. It’s interesting that the torque reading peaks at around 420ft.lb. and is pretty flat except on the shifts and the initial torque spike on launch (TCU causing the bog due to torque spike?)

#5

Looks good.

The nose over is going to be the load and weight of the car being picked up by the motor power but since there is not enough forward momentum yet the weight of the car drags down the motor and starts to pull the car along. Once enough momentum is created the cars physcal acceleration catches up with the motor acceleration.

So its a power bog. putting a taste more air in the tires will help with a slight wheel spin and in most cases if you add enough less bog. The obvious idea is getting rid of as much rolling resistance as possible. This is why lots of guys gut there cars out… Im not a fan but it helps the dead stop acceleration.

The spike your seeing is the initial clutch clamp tq

As for VCDS. I agree My car uses the other log version so I can’t really log that many blocks anyways but I have used VCDS and you are limited by how many you can log before you get a crapy sample rate. I guess thats what happens when your trying to comminicate too much over one line.

I use axcel to plot and make graphs so I have been used to it by now. I like graphs for a general over view. You can change resolution as needed. For me its always been useful for a quick look over the entire log but for me. Line data has always been the most helpful when really picking something apart.

#6

Kind an off topic question, but logging related. I cannot access the “advanced measuring values” to pick and choose which parameters I want to log. I can only access the “measuring blocks” option. Is this normal for the B8 4.2 S5s?

#7

yes the VCDS stuff was more in the I think 2012 and up cars. The older cars with the older me9 ecus just had measuring blocks. Not a bad system of logging just not VCDS