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Pt.2: user programmable systems vary the maps Automotive Ignition Timing Programmable engine management ECUs are now allowing specialist manufacturers to devise their own ignition maps. Here’s a quick look at what’s involved. By JULIAN EDGAR The use of programmable engine management ECUs has meant that ignition timing maps can be developed which take into ac­count more than just load and engine speed. Correction for vary­ing intake air and engine coolant temperatures can be provided and much greater advance can be specified than was possible with conventional distributors. While initially affecting only those developing highly-modified road cars or race machines, the freedom of having total ignition timing control meant that new fields had to be explored. Craig Allan is one of the few people formally qualified (he has a Diploma in Engineering) and also active in the modified automo­tives field. Working with son Adam, the Adelaide-based principal of Allan Engineering says: “What computer engine management The advent of programmable engine management ECUs has meant that there is total freedom in devising ignition maps. Any advance can be specified at any load and RPM, with corrections able to be made on the basis of input from the coolant and inlet air temperature sensors, knock sensor and so on. 4  Silicon Chip did was teach us that we still had a lot of learning to do”. With manufacturers selling programmable engine management systems in the field, there was also a need for a major educational campaign. Australian manufacturer Invent Engineering (maker of Haltech programmable engine management ECUs) decided that a formal warning about the dangers of improper ignition timing should preface the running of their software. “WARNING: Poorly adjusted ignition timing can damage your engine... Engine failure can cause an engine to explode and cause a potential vehicle accident ...” reads their statement in part. It goes on to suggest that you return their product if you are unhappy with this idea! However, for the programmable engine management manufactur­ ers to be able to sell their products, some ignition timing guidelines are needed. Ironically – considering the gravity of their warning – Haltech are amongst the best in facilitating the development of ignition maps. The QuickMAP system used by their proprietary software requires only the input of an 8-digit alphanumeric code to configure an ignition timing map for all engine loads. An example of the code used is ‘15A38D10’. This is trans­ lated as follows: • 15 – ignition timing advance angle at idle; • A – 1500 RPM for full ignition advance (‘A’ indicates 1500 RPM, ‘B’ 2000 RPM, etc); • 38 – full load ignition advance angle; • D – an additional 9° light load advance (‘D’ indicates 9°, with each g/kWh αz SPECIFIC FUEL CONSUMPTION 580 20° 540 500 30° 460 40° 420 50° 380 340 g/kWh 50° 12 40° 10 30° HC EMISSIONS 8 additional alphabet placing from ‘B’ meaning another 3°); • 10 – ignition timing retard angle under boost (when using a turbo or other supercharger). The resultant ignition timing map is not intended to be the final product but it provides a good starting point for subse­quent tuning. An example of the type of timing map produced with this system is shown in Fig.5. It is for all loads, from -100kPa manifold pressure to more than +100kPa boost at 4000 RPM on a turbocharged engine. The arbitrary reduction under boost condi­tions provided by the QuickMAP is readily apparent; this sudden step would be smoothed in due course by the operator to provide an ignition advance which varied more in keeping with the actual turbocharger boost pressure. Incidentally, like almost all pro­ grammable engine management systems, the Haltech approach uses a MAP (manifold absolute pressure) sensor to determine load, rather than an airflow meter. The production of an ignition map for the Haltech system takes only a few moments, while for some programmable systems several hours would need to be spent programming each load site. Interestingly, when using a chassis dynamometer to tune this Haltech system on a Nissan FJ20 turbocharged engine, the author and mechanic Paul Keen found detonation intruding at about 2000 RPM on 25kPa boost. A revised QuickMAP incorporating 15° of boost retard (versus the original 10°) cured the prob­lem, with the speed of the remedy impressive. Another programmable engine management manufacturer gives an example of a ‘very basic’ ignition advance curve. Advanced Engine Management Systems (manufacturer of the Wolf 3D system) provides a table of ignition advances and engine speeds. It looks, in part, as shown in Table 1. The reason for the timing being more advanced at 500 RPM than at 1000 RPM is to provide a stable idle speed. This occurs because if the engine starts to slow down from its designated idle setting, the greater ignition advance causes the engine to produce more torque, thereby increasing the engine speed back to its correct value. Tuning ignition maps Given that incorrect timing can cause major engine damage or at the least degrade performance, the tuning Table 1: Basic Ignition Timing Advance RPM 500 1000 1500 2000 2500 Advance 10° 8° 12° 15° 17° 20° 6 4 2 0 0.7 0.8 0.9 1.0 1.1 AIR RATIO λ 1.2 1.3 1.4 Fig.1: the ignition timing which gives the best hydrocarbons emissions also gives the worse specific fuel consumption. Devis­ing an ignition map which is optimal depends on the engine’s application. (Bosch) 50° b 40° 30° ADVANCE ANGLE AFTER TDC BEFORE TDC The use of a chassis or engine dynamometer allows the best tuning of the ignition map. Torque output, exhaust gas analysis and combustion temperature can all be monitored. αz a 20° d 10° 0° c 10° 20° 0 1000 2000 ENGINE SPEED 3000 REV/MIN Fig.2: retarding the ignition timing to after TDC is useful for reducing exhaust emissions. In the above graph, ‘a’ is the timing curve for full load, ‘b’ is for part load, ‘c’ is at idle and ‘d’ is when the vehicle is overrunning the engine. (Bosch) of the ignition map is critical. Most people programming engine management sys­tems use a chassis dyna­ mometer, where power and torque readings at the driving wheels can be measured. Others use an engine dynamometer which requires the engine to be removed from the vehicle for the initial tuning. Depending on the quantity and quality of the instrumenta­tion available, exhaust gas analysis, combustion temperatures, torque output and other factors may be measured, or the ignition October 1995  5 ever, because the most common use of programmable engine management is in motor sport or road-performance applications, most systems are set up for maxi­mum power combined with good driveability. Paul Keen is another mechanic who is well-used to setting up ignition timing systems. Over years of tuning mechanical advance systems on a chassis dyno, he has developed several rules of thumb which provide starting points for further refinement. Generally, he finds that, on 4-cylinder engines, a total advance of 36° is appropriate, with 32° total being used on sixes. The variation with V8s is wider, any­ where from 28-36° being used, depending on the engine and its state of tune. The variation relates more to combustion chamber design than any other factor: 4-cylinder engines (especially in the past) are better in this area than the larger engines. Turbocharged engines require ignition retard when on boost and lots of advance when at part loads. This previously difficult task is eased by the use of programmable ignition systems. tuning may be carried out using just the operator’s ears to listen for knocking. No ignition map is ever perfect and so the operator’s skill plays a large part in setting the optimum timing for the engine’s particular application. For example, the ignition timing map which gives the best results for fuel consumption is not the best for NOx emissions. In addition, a map designed to give maximum power with higher octane fuel will have poor knock-resistance if used in a vehicle subjected to varying fuel quality. How- Idle speed advance The appropriate idle advance relates more to the engine compression ratio than to any other factor, suggests Adam Allan. Engines with a IGNITION ANGLE °BTDC 40 LO AD RPM SIG NA L D E SPEE ENGIN 0 IGNITION ANGLE °BTDC IGNITION ADVANCE 35 30 25 90 20 80 15 70 10 60 5 50 40 AD RPM SIG NA L E 0 ENGIN SPEED Fig.3: these are Bosch Motronic ignition maps. The top is for premium fuel, while the bottom map is for regular fuel. While virtually identical in the low-load range, at higher loads the ‘premium’ map uses more advance. (Bosch) 6  Silicon Chip 0 7500 6500 10 7000 5500 20 6000 RPM LO LOAD 30 4500 5000 3000 3500 4000 0 Fig.4: part of an ignition map from a 418kW (560 bhp) Group A Holden V8. The advance is highest at low loads and RPM. Note the required ‘peaks’ and ‘valleys’ as a result of tuning the engine on a dynamometer. Fig.5: the QuickMAP facility of Haltech programmable engine management allows the production of ignition maps with the input of just an 8-digit code. This provides the starting point for further modifications. Fig.6: this Haltech ignition curve is for 3000 RPM on a tur­bocharged engine. Each of the individual bars on the curve can be raised or lowered to give timing changes at each load site. Fig.7: this correction chart allows the ignition timing to be changed on the basis of coolant temperature. Note the increase in timing advance at low temperatures and the decrease when the engine is overheating. Fig.8: this correction chart allows ignition retard to be pro­grammed for when induction air temperatures are high. This is especially required in a turbocharged car which does not have effective intercooling. compression ratio of 8:1 will accept an ignition advance of anything from 0-20° without kickback on star­ting. A 10:1 compression ratio will reduce this to 15°, 11:1 to around 10-12°, while race engines using the very high compression ratios of 12:1 or 13:1 can sometimes tolerate no ignition idle advance at all. The rate at which the timing advances from the static (or idle) timing is another variable. “Some engines like an early full advance and others don’t”, said Paul Keen. “The Falcon cross-flow six, for example, pings with an early full advance.” Adam Allan suggests that the point at which maximum timing ad­vance is reached should correspond to the RPM at which the wide-open throttle engine’s torque output has started to decline. If exhaust gas temperature readings are being made, he suggests that optimal ignition timing is that which gives the lowest exhaust gas temperature combined with timing advanced sufficiently to give maximum torque. A 2-3° retard of the advance angle from the point of detonation provides a sufficient safety margin, he believes. At light loads, as used in everyday cruise conditions, an advance of up to 40° will improve responsiveness and economy. This figure is greater than generally used by tradition­al mechanically controlled timing systems but is easily achievable with programmable ignition. Adam Allan has seen this advance used successfully on many engines, even those with an 11:1 com­ pres­sion ratio and running on Avgas. Examples of ignition maps While programmable ECU ignition maps are the result of many hours spent using dynos and so are intellectual property worth thousands of dollars, we managed to find two sources prepared to reveal some of this information. Paul Keen of Adelaide’s Dar­l­ing­­ton Auto Tune allowed access to Haltech E6 software maps devel­ oped for a turbocharged FJ20 2-litre Nissan engine, while Craig and Adam Allan released ignition maps written using Autronic SMII software for a Holden Group A racing V8 and for a Ford 289 V8. Fig.4 shows the ignition advance map for 3000-7500 RPM of the Group A V8. Using a 10:1 compression ratio and a high octane fuel, a maximum power output of 418kW at 7100 RPM was measured. As expected, the advance at low loads remains high (at 40°) until 5000 RPM but drops to just 5° at 7500 RPM. Low loads at 7500 RPM would simply not be seen in this October 1995  7 occurs under positive manifold pres­ sure; ie, when boost is provided by the turbo. Fig.7 shows a correction chart based on coolant tempera­ture. Up to 10° of advance or retard can be used to modify the map developed on the basis of load and RPM. While this map shows no modification of the timing for the temperatures which would be realised in normal running, the height of these bars can all be changed – meaning that ignition timing can be modified on the basis of coolant temperature with great resolution, if desired. The second of the Haltech ignition correction charts (Fig.8) has even more potential, especially in turbo engines. Turbochargers heat the intake air as they compress it and a hot induction charge is much more likely to cause detonation than one at ambient temperatures. Intercooling is often provided to reduce the possibility of detonation and to increase power. However, an ignition map which can reduce the amount of ignition advance on the basis of air inlet temperature has the potential to allow very high engine efficiencies by running boost timing which is retarded only a little – but which greatly reduces the timing advance as the air inlet temperature increases. A laptop PC, a chassis dynamometer with power and torque readouts, exhaust gas analysis equipment and a skilled operator are needed to set up programmable ignition (and fuel) ECUs. 40 35 IGNITION ADVANCE, DEGREES BTDC 30 25 20 Idle ignition curve 15 10 5 0 300 ENGINE RPM 1000 Fig.9: idle ignition advance curve, Ford 289 V8 with Autronic programmable engine management. The idle speed is made self-stabilising to some degree by the use of this low RPM timing curve. race engine and so little dyno tuning was carried out in this area. As loads increase, the ignition advance is greater at all RPM and is nothing like the curve provided by mechanical advance mechanisms. However, of greatest interest are the required peaks and troughs in this ignition map, which was developed with the engine being loaded by an eddy-current engine dynamometer and with full data logging being used. 8  Silicon Chip Incidentally, Fig.4 was drawn from the Autronic program data (which is normally expressed in tabular form) using Excel software. The ignition maps shown here for the FJ20 turbo engine are printed directly from the Haltech E6 program which uses on-screen bargraphs to show the ignition advance. Fig.6 shows a 3000 RPM ignition timing map, with load on the horizontal axis. Note the reduction in advance which Fig.9 shows the idle ignition curve for a 289 Ford V8 with Autronic programmable engine management. The car uses an automat­ ic transmission and does not have an air idle-speed control valve, meaning that idle speed control when the car is placed in and out of ‘drive’ is carried out mostly by ignition control. The 300 RPM advance of 12° is for starting while the 34° advance at 450 RPM helps bring the engine back up to idle speed when sudden loads are placed on it. The advance of only 5° at 1000 RPM helps slow the engine, bringing it back to the correct idle SC RPM. Acknowledgements Thanks to Allan Engineering (085) 22 1901 and Darlington Auto Tune (08) 277 4222, both of Adelaide, SA, for their assistance in the preparation of this article.