Ignition Tuning Ideas for Turbos
04/13/99 Updated 05/31/01, 12/20/99, 02/19/03, 07/10/03
This article details the basics of tuning a turbocharged engine running on pump fuel. You will be programming 2 different parameters here, RPM IGNITION and IGN RET/MAN PRESS. The RPM parameter has a timing slot every 250 rpm on most systems. The timing at idle is usually in the 5 to 15 degree range on most engines, 10 being a good starting point. From this point, most engines will run well if you add around 3 degrees per location, with full advance being acheived at 2500 to 3000 rpm. With SDS and most engines, you should avoid more than 30-35 degrees total timing at rpms below 2500. This is counterproductive to power, longevity can cause high current draw on F type coil packs leading to blown fuses and possible failure.
Most engines like between 28 and 38 degrees of advance for maximum power. Most small bore engines with good plug locations, are happy with 30 to 35 degrees. Once you get to around 3000 rpm, the same advance value can be entered the rest of the way up the chart.
With low octane pump fuel, your engine will likely detonate a lot with these basic settings so you will have to enter retard values in the IGN RET/MAN PRESS windows. These tell the ECU to retard ignition timing at a certain boost or manifold pressure. By entering a 2 at 4psi, you would get 2 degrees of retard at 4 pounds of boost. Most engines will require increasing amounts of ignition retard as the boost pressure increases. The amount depends on many factors including the particular engine, compression ratio and the fuel being used
To get reasonable fuel economy, most engines advance the timing past the point where maximum, wide open throttle power is obtained. Since most street engines are cruised in the 2750 to 3750 rpm range, extra timing can be added here if this is a concern. You might add something like 4 to 5 degrees.
Most engines encounter the worst detonation in the rpm range where maximum torque is produced. Most import street turbos find this in the 3750 to 5000 rpm range, although this can vary widely depending on turbo matching. Since this range is mostly above where the engine is normally cruised, timing can be pulled back here without impacting economy. In fact, timing will usually have to be retarded below what is required for maximum power at high rpm in this rpm range. This retard will not be required on high octane fuel usually. It should be noted that most performance turbos make very little boost below 3000 rpm so detonation is usually not a great concern below this rpm.
As you can see, the engine requires different amounts of timing under different conditions. How do we mesh all of this together? Below is a sample ignition map for a 2400cc turbo. Torque peak is in the 3750 to 4750 rpm range so we pull back the RPM timing values in this area. Highway cruising is in the 2750 to 3500 rpm range so we add a few more degrees here. Timing above the max torque range can be re-advanced a bit as peak cylinder pressures fall off. Boost retard starts very low on this engine because it has a high compression ratio. Remember: total timing is the result of the RPM timing minus the boost retard value under a given condition.
RPM IgnitionValue
1000 12
1250 15
1500 18
1750 21
2000 24
2250 27
2500 30
2750 35
3000 36
3250 36
3500 36
3750 35
4000 31
4250 30
4500 30
4750 30
5000 32
5250 33
5500 33
5750 33
6000 33
6250 33
6500 33
