Text by AJ Hunsinger // Photos by AJ Hunsinger
Tonight, I decided to work on my ignition (timing) maps. I have noticed for awhile now that my car seems to “come to life” and pull harder just before my set rev limiter, which is just over 7000RPM. It seemed kind of odd because I am using an Evo III 16G turbo, which isn’t “that” big in the DSM world. Which means it should be hitting peak boost well below my rev limiter.
First, we need to do some single gear pulls while logging, preferably 3rd gear, from about 3,000RPM to redline. If you aren’t logging boost, it is important to watch your boost gauge and find out when you transition from vacuum to boost with your turbo.
Next, look over your logs. At the beginning of a pull, before peak load, you want your timing to gradually decrease throughout the RPM range. After peak load, you want your timing to gradually increase. The faster the engine RPM, the faster you need fuel and spark to be ignited in the combustion chamber. But, it is important to keep in mind that as load increases, the timing needs to decrease.
Now, find your peak efficiency (where the engine makes peak torque). This will be the absolute highest amount of load throughout your WOT pull in your log. On the lower side of peak efficiency (left side of peak efficiency on your ignition map), you want your timing to gradually decrease as it gets closer to peak efficiency. On the higher side of peak efficiency, you want your timing to gradually increase throughout RPM range.
Your timing at peak efficiency needs to be the lowest amount of timing throughout your WOT pull.
Below are examples of my ignition timing curves in relation to RPM and Load. The first is my ignition map and the next is my log.
Every car and setup is different. The turbo, amount of boost, fuel mods, air/fuel ratio, etc. all play a factor when building ignition maps and adding timing. Your rev limiter or shift RPM point determines a lot as well.
Start with a base ignition map and gradually increase timing. You should set a target boost pressure and AFR before adding any timing. Which means you need to adjust your boost controller to where you want your target boost and dial in your fuel injectors and building your fuel maps. As you are increasing boost to your target boost level, make sure you monitor knock.
Slowly raise your ignition timing in your ignition timing maps 1 or 2 degrees at a time throughout the RPM range and load curve. If you reach your target peak timing without getting any knock, you can stop adding timing and be done, stop adding timing and raise boost until you reach either your new target boost or get knock, or you can leave boost alone and add more timing until you get knock. Regardless, once you get knock, you need to lower your timing.
There are several different methods on how to approach timing, boost, and AFR. I will explain what I do personally and what has worked the best for me.
First, I set my target boost where I want it, of course while checking for knock and logging through the entire process. When I last built my ignition maps, my target boost was 25PSI.
Once I got my boost levels to 25PSI, I slowly started raising my timing. I had an idea of what I wanted my peak timing to be, around 17-19 degrees.
Once I began getting knock, around 20 degrees, I backed the timing off a couple of degrees which eliminated knock. I left my peak timing around 17-18 degrees.
Every pull is different. In the log pictured above, my peak timing was only 15*. But, I let off at 6400RPM. When I go higher with RPM in a WOT pull, say 7000RPM, I am generally around 17-18*. The more RPM you turn throughout a WOT pull (after peak efficiency), the more timing you will reach. If you begin knocking in higher RPM, closer to where you want to shift at, you need to lower peak timing.
Peak timing is determined on how high of an RPM you plan to reach. If you let off at 6500RPM, your peak timing will be maybe 16 degrees. But on the same ignition map and turning 7000RPM, your peak timing will now be higher, say 19 degrees for example. Your rev limiter plays a huge role in peak timing.
Getting back to the peak efficiency thing, again, you want your peak efficiency to be at the lowest timing level during a WOT pull. Further more, you want anything to the right of your peak efficiency cell have lower timing.
Peak efficiency is the highest amount of load that your ECU sees at any given time, specifically during a WOT pull. You should also keep in mind that if you are seeing 280 max load for example, you need to give yourself a small buffer. Extreme temperature changes, increased boost levels, etc will cause you to reach higher (or lower) load cells.
Using my ignition map for example, my max load is 280 in the log I posted above, which is normally right where my max load always is. If this log was done in the summer in 90 degree weather, well doing a WOT pull in the winter with 20 degree whether will easily cause me to reach a higher load count, maybe 290 or 300.
In my ignition map, my load cell at 280 at peak efficiency is 9 degrees. In the same RPM range, load cell 290 is 8 degrees. 300 is 8 degrees. Then from 310 load and on, drastically gets lower as it drops down to 4 degrees, then 3 degrees. This is a safety blanket, more or less.
Say you are doing a pull and all of a sudden your wastegate vacuum line pops off or something happens that causes an overboosting problem. Well now, you will be surely reach dangerously high load cells. If this happens, you don’t want nearly as much ignition timing. Otherwise, you could easily damage your engine from getting a significant amount of knock, detonation, lean AFR, etc.
I have also experimented with adding timing vs. adding boost. With higher boost and lower timing (with no knock), I made a LOT less power than running lower boost and higher timing. When I tune my cars, I always tune for maximum timing without knock.
Hopefully this article helps you understand the concept of adding timing a little better. I will try to add to this at some point. For now, it is a good basic explanation of how it all works.