Now that I was done getting ready, I started making some changes that would actually have an effect on the output of my engine.  I started to tailor my boost curve to how I wanted it.  My main goal here was to maximize the torque I could get out of the turbo at any given point.  To that end, I altered the Boost Targets table to have a pretty high level of boost in the middle rpm ranges and then tapered that towards redline to prevent asking the turbo to spin past its efficiency range.  Although this map has pretty clear cut targets specified in PSI, it’s not the only thing you have to tune to get your boost where you want it.  The Stock ECM has a very capable and thus very complex boost control scheme, including many correction factors.  All this table does is give the ECM a target to shoot for when applying the values from the many correction tables.  If you make a change and your boost isn’t changing, you probably need to alter the Wastegate Duty Cycle table to move their values into a range that lets your car hit the values in the Target Boost Map.  By the time I had finished tweaking this and the other maps associated with wastegate duty cycle, I had a nice stable boost curve that would shoot rapidly to target boost at any rpm or throttle input speed and remain there without wavering or spiking and then taper smoothly to redline.

Tuning the primary fuel table is perhaps one of the most sensitive areas.  Here, you have the ability to run the car so lean that it detonates at the slightest application of throttle or so rich that it rinses the cylinder walls of all their oil.  Either way, you could expect engine failure.  The goal here is to use enough fuel that you’re making the most of the air your turbo is delivering, but not so much that you’re excessively cooling the combustion and sucking out power.  It is important to realize that the values shown in the Primary Fuel table are not the exact air fuel ratios that will be run.  They are just there for an approximate reference to help you make your map without relying on totally arbitrary numbers like some other systems do.  To that end, change the values until you see the results you want in your logs of the Wideband O2 sensor.  I have heard a lot of people in the past say you should run around 10.5:1.  In my opinion, that’s too rich.  I’ve got mine set to more like 12:1 during turbo spoolup, 11.5:1 around torque peak and then dropping slowly to around 11:1 by redline.  It seems to run well this way and the extra heat during spoolup helps build boost a little more emphatically.  Before you start removing fuel from the base map, it’s a good idea to first remove some timing from your ignition maps.  This will ensure that there is plenty of headroom while you’re zeroing in on your air fuel targets.  You really don’t want to run the timing you’d run for a 10:1 setup with 12:1 and cause a major detonation event.  

Moving on to ignition timing, it’s important to understand what you’re changing and why it makes a difference.  I’ve heard a lot of people say “more timing, more power”.  This is just not true.  The torque your engine puts out is going to be at its maximum at a very specific ignition advance.  If you run less advance, you get less power.  If you run more advance, you get less power (and also probably some detonation to ruin your day).  Internal Combustion experts refer to this as “MBT Timing” which stands for Maximum Brake Torque Timing.  What it means is that you are looking for the amount of ignition advance that gives the best engine torque without causing knock.  To help you zero in on this magical amount of timing, you can use a couple different methods.  The first, and probably easiest, is a load-based dynamometer.  With it, you can make changes to the timing and watch the torque change.  If torque goes up without knock, then you’ve made a good change.  Not everybody has a dynamometer in their garage though, so on to more plebian methods.  The most reliable way is to use a combination of a knock sensor that you can listen to or watch, and a road dyno program that analyses your logs of rpm vs time to give you a torque graph.  Just start from a very low timing and increase it until the torque stops increasing or the knock meter starts going crazy.  If you reach knock, back it off.

Once you’ve hit boost, fuel, and timing, you will likely see that some things need your attention again.  Changing the fuel and timing may alter how your turbo spools because of the inherent energy in the exhaust stream.  For this purpose, tuning becomes not just a wham-bam-thank-you-ma’am, but rather a continuous cycle of improvement, always zeroing in on perfection.  It’s important to make small changes one at a time.  Never change several different parameters because then you lose your frame of reference for what your changes are doing to the car.  You will maintain a much higher level of sanity if you keep it slow and easy.

It all sounds pretty simple, right?  I’ll leave that up to the reader to determine.  I, personally, am nowhere near mastering this process and can definitely see why a professional tuner gets to command the prices they do.  This is a lot of work and knowing how it all ties together is extremely important to get the best power while still maintaining a reasonable safety margin.  I am learning more all the time and growing more confident in my abilities.  I am on the verge of having a professional tune my car just to see what he does differently, in hopes of learning something that I can use.  Overall though, I’d say it’s very worthwhile to learn this stuff yourself because what you take away is more than just a tuned car.  You get to understand more about how it works and that has tremendous implications for the rest of your modification trail.

Happy Tuning!