Cobb AccessTUNER Race (ATR) Tuning Tips – Requested Load vs Actual Load
Posted on 26 June 2012
Tuning the N54 is now completely possible thanks to www.cobbtuning.com and their Cobb AP handheld. Their OTS (Off-the-Shelf) maps are a great start for your N54 powered BMW car. With the release of AccessTUNER Race you can now custom tune your car to perform like it never has before. Some other tuning platforms give you tables or sliding scales to modify, but Cobb has taken it to another level giving you access to over 70 tables in the DME. These tables will allow you to make the power you have been craving.
The Cobb AP uses load targets to control boost. This may be new to some of you who have either never tuned a car in the past, have tuned but only with hardware that utilizes boost targeting systems, or have dabbled but still struggling to feel comfortable changing how your car is controlled. If you fall into any of these categories or just want a refresher – here comes Load Tuning for boost 101.
A hot topic on the forums has been people noticing that their Actual Loads do not hit their Requested Loads. Common sense tells us that we are requesting a value so the car should be able to hit that value. It is not that straight forward. Cobb has done a lot of the work for us and set up a very safe and reliable situation for us to tune our cars and not have to worry about over-boosting or damaging components.
This is what the main load table looks like:
I have entered 190 as the load target throughout my RPM range and tapered it off slightly up top as the turbos simply leave their efficiency range. When I flash this table to the car and go log I see that my Actual Load never really hits 190. I spool up and peak at about 182 and then it drops and holds in the mid 170s. The reason for this is that the car is referencing many different limit tables, WGDCtables, PID settings, etc. This is NORMAL. The car will run the minimum boost to hit the Requested Load based on all of the calculations and limiting tables / “nannies”. The stock WGDC tables are setup to run our stock turbos to the limits of their efficient range so you can make a lot of power without changing the boost control setup (i.e. I am not hitting my Requested Load but my car is running strong and doing exactly what it should).
One of the things that comes to mind at this point is “How do I know that my car is doing what it is supposed to?” When I log I monitor many different things. To make sure that I am running the boost I want to run I log Boost Req Abs and Boost Mean Abs. These two parameters are the boost the car is requesting and the boost your car is making. The values are in addition to standard atmospheric pressure of 14.7psi. When you see the car requesting 32.97 in a log that is really only requesting that the car generate (as a reading on your boost gauge) 18.27psi and NOT 32.97psi. If you track what the car is requesting and what the car is actually making you should expect to see that the values are very close. In the lower to middle range of the RPMs you will see that they are very close and as you reach the upper RPMS (depending on how much boost you are requesting) the difference may be slightly larger. We expect that the small stock turbos will taper off a bit in the upper RPMS and if you are requesting too much there may be more of a variance in actual vs requested. If you have large differences in these two values after fully spooling you may have a small leak somewhere.
There is significantly more you can do with the boost tables through ATR, however for stock turbos following what I have discussed here is a great start and more than enough to get you on the path to trapping in the high 117+range (with the required supporting mods). You will need more than just a strong load curve to get there but this a great start to reaching your goals.
You guys can always reach me here or on the forums. For now – open up ATR and get started!! If you need help or want a tune you know how to reach us.