When tuning a car for any application, there are two main things a tuner looks at: the Air/Fuel Ratio (AFR) and the ignition timing. In other words, they are looking at the amount of fuel going into the internal combustion engine and when to ignite it with a spark. I’ve already written up an article to explain AFR’s, so check that out to get an understanding of how they work and what to look for when tuning an internal combustion engine.
This article is meant to explain ignition timing. Once you have taken an engine apart and put it back together, you start to realize that it isn’t as mysterious as it once seemed. For me, my first rebuild was the scariest thing I had done. Now, they seem to fall apart and reassemble without me having to think about it. Tuning is the same situation; when you utilize the proper tools, it’s a simple (but long) process.
If you have heard about pre-ignition and pre-detonation, you may not know that these two terms have very different meanings:
- Pre-detonation is caused by a foreign object that forces the intake charge to react before the tune intends it to. It doesn’t have to do with the spark of your tune. Examples being: hot, flaked-off pieces of carbon from your valves, too much oil in the intake charge, or a spark plug tip glowing red hot and acting like a diesel’s glow plug.
- Pre-ignition has to do with how aggressive the ignition timing of the tune is. It is the timing of your spark plug.
If you look at the graph below, it shows that if the spark is fired too late, then combustion happens after the piston reaches top dead center. If the piston is already traveling down when the spark is fired, the opportunities for power aren’t as high as they could be. Power is lost if the spark is not fired when cylinder pressure is at the highest the fuel will allow. When the spark is fired too early, problems occur.
Say we have an engine that is running and it’s revving at 6,500 RPM’s, so our pistons are reaching speeds of almost 30 mph in just over a 3 inch space. As it comes to a complete stop, the connecting rod spins its last few millimeters up and over before being able to move the piston down. Every part of this process is timed perfectly so that we can have a smooth operation. If the tune advances your ignition too far, the spark is fired so that the intake charge ignites before the piston reaches top dead center. Imagine that piston is charging the to the top of the cylinder at almost 30 mph, and then BOOM half an inch before top dead center, the intake charge is ignited by the spark! The violent explosion that normally pushes the piston down to bottom dead center is trying to do the same thing when the piston is still traveling up in the middle of the compression stroke. This creates a huge disruption in the whole motor; nothing can spin correctly because one of its parts has been slowed significantly. This disruption is what we call “knock”.
Now going a little bit more in depth, the spark isn’t fired correctly when it reaches top dead center (TDC). It takes time for the intake charge to ignite and for cylinder pressures to increase. As the charge begins to ignite, a flame front is created that spreads throughout the top of the piston. Cylinder pressures do not reach their max until 18-20% of the intake charge has been burned, so when it comes to ignition timing the spark can be fired slightly before the piston is at TDC. If it is timed so that 18% of the intake charge has burned at TDC, the reaction can occur when the piston is at the top of the cylinder and squeezing the intake charge tight, thereby creating the most energy for the most power.
When it comes to actually figuring out when to fire the spark, a tuner obviously can’t actually be watching what is happening in the cylinder. In the old days of carburetors and distributors, tuners would listen for an audible knock in the cylinders and then correct the timing accordingly. With our current technology, we have knock sensors that pick up on vibrations in the motor that otherwise wouldn’t be audible to the ears. If the knock sensor feels a tremor in the block around the time that Cylinder 4 is firing, it knows that the ignition of Cylinder 4 is not right. Modern tuners use these sensors while tuning a vehicle on a chassis dyno. This allows them to set the ignition timing as aggressively as possible to get a perfectly timed reaction to the intake charge.
I have been told about a device that has amazing results in safely controlling ignition timing. It’s made by J and S electronics and seems to be a one-of-a-kind product on the market. “J&S Electronics has developed the Safe Guard which uses a knock sensor to provide feedback to its microprocessor which, in turn, controls the timing for each cylinder on an individual, optimized basis”. From what I have read on it, Safe Guard seems to sense knocks individually and can advance and retard timing for each cylinder separately. As I mentioned in my turbo EJ22E article, I have a forum friend that ran this product and a water meth injection kit on a stock block at 16 psi for several months. He swears that there was zero audible knock and the Safe Guard pulled timing perfectly! Check that out!