A few people have asked me about the differences between the standard Pulsar and Sunny GTiR maps. I mentioned before that the Sunny maps are a lot more conservative, but I wasn't able to provide any "hard evidence" to support this. For this post, I will only concentrate on the fuel and timing maps for normal operating conditions (i.e. not including 'knock' maps which are switched to automatically when the sensors detect knock). I will break up the information into "fuel" and "timing" sections to help make it easier to digest. Enjoy!
What I've done is download the fuel maps for both the Pulsar and Sunny models, and compute the Air/Fuel ratios that the ECU is trying to achieve for a variety of engine RPMs and loads. Bare in mind that the stoichiometric ratio for combustion is around 14.7:1, which gives the most efficient burn of the fuel in the combustion chamber. During idle (and indeed most low-load/low-RPM scenarios) the engine tries to achieve this ratio by forcing a closed loop with the stock lambda sensor. However, once the engine load increases and the RPMs rise, it makes sense to add a little extra fuel to combat knock, which can result in catastrophic failure of your engine if not eliminated. Unfortunately, the standard maps are VERY conservative. Below is the standard Pulsar fuel map:
You will see that at high load and high RPM values, the A/F ratio that is trying to be achieved is around 10. This is VERY conservative. It gets even worse when you look at the Sunny map:
Here, the Sunny ECU is trying to hit A/F ratios of around 9!!!!!!!! This is drastic over-fuelling, especially for a stock car. Also, notice that the maps are not particularly smooth. The right panels of both images show a 3D plot of the fuel maps, and you'll see that there are lots of bumps and spikes, which tend to make the transition on to boost quite poor. Even by smoothing these bumps out the car becomes a little more pleasant to drive, but the real benefits arise once the fuelling is reduced for high RPM and high load values. It is commonly assumed that an A/F ratio of around 11-12 is good for high RPM and high load areas of the map.
OK, now I've downloaded the timing maps from both the standard Sunny GTiR and Pulsar GTiR ECUs. First up we have the standard Pulsar GTiR timing:
The values listed here represent the angle BTDC (before top dead centre) when the spark plug is fired to start the burn process. Top dead centre occurs when the piston is closest to the cylinder head on it's compression stroke (i.e. just before it starts to move downwards again on its 'power' stroke). If all of the fuel in the combustion chamber burned immediately upon the spark plug firing, then you would want to fire the spark plug approximately 20 degrees ATDC (after top dead centre). This way, the piston would already be starting its downward motion and the immediate burn of the fuel would cause maximum acceleration of the piston on its power stroke (hence producing maximum torque!). However, this is an ideal scenario, and not one which we encounter in a real internal combustion engine Instead, the fuel does not burn immediately, and unfortunately takes a while before all of the fuel vapour has been completely ignited. As a result, we have to start the ignition process before the piston has reached the top of its compression stroke (i.e. a number of degrees BTDC), so that all the fuel has been burned a short time after the piston reaches TDC, thus providing optimum torque readings. This is called "ignition advance" because you are commencing the burn before (i.e. in 'advance' of) the piston reaches TDC.
Have a look at the ignition timing when the Pulsar GTiR engine is at idle with no load. You will see that the ignition timing here is "20", which refers to 20 degrees BTDC. This is why people use a timing gun to check that the idle ignition is around 20 degrees BTDC in order for it to be in sync with what the ECU wants. As engine RPM increases, the ignition timing will need to become more advanced (i.e. a larger angle BTDC) so that the fuel vapour has the correct amount of time to fully burn. This is quite simple to understand since as the engine speed (RPM) increases, the time available to burn the mixture decreases (more revolutions occurring each second) but the burning process itself proceeds at the same speed. Therefore, the ignition needs to be started earlier as the RPM increases in order to complete combustion in time for the start of the 'power' stroke shortly after TDC. Take a look at the load column (16): at idle the ignition timing is 20 degrees BTDC, rising to 50 degrees BTDC at 6800 RPM.
The problem arises when you start dealing with high engine loads. These could be an effect of hot engine temperatures, high boost levels, or even something simple like driving up a hill. Under these conditions the ignition timing is also dependent on the specific load applied to the engine. Here, more load (i.e. at full throttle) will result in a larger throttle opening (supplying more air into the cylinders), ultimately allowing the fuel vapour to burn more easily and in a faster time. Under these conditions, less ignition advance is required since the burn process may be more efficient due to efficient filling of the combustion chambers with air. This is called "ignition retardation" because you are commencing the burn later (i.e. closer to TDC) in the engine cycle. Take a look at the RPM row for (6400): with minimal engine load the ignition timing is 50 degrees BTDC, decreasing to 26 degrees BTDC at high load values.
Also, retarding the ignition with higher engine loads is a good way to help prevent knock. At higher engine loads, the engine is likely to be physically hotter, and this may assist the burn process complete in a very rapid time. If you kept the ignition timing 50 degrees BTDC and the burn process occurred very rapidly, then you may find that the burn process has completed before the 'power' stroke has even started. This means that the forces created by the burning fuel push against the rising piston (remember, if the piston is BTDC it will still be on its compression stroke), thus slowing it down and creating no assistance once the piston begins its downward motion of the 'power' stroke. Best-case scenario will result in reduced power (remember highest power results when the burn process completes shortly into the 'power' stroke, i.e. ATDC). Worst-case scenario is complete engine destruction as the forces may be so strong that substantial 'knock' or 'pinking' occurs, causing cylinder and/or piston damage. Therefore, as a safety factor, most ECUs incorporate very safe timing angles at high engine loads. Take a look at the point on the timing where an engine may be coming on to boost with the throttle fully open (i.e. 3200 RPM and load 86): here the ignition timing is 16 degrees BTDC - a very conservative timing to insure that no knock/pinking occurs - basically putting engine longevity ahead of absolute power.
Now take a look at the standard Sunny GTiR timing map:
You will immediately see that the base timing (i.e. idle with no engine load) is identical to that of the Pulsar GTiR. This is why you can set your timing with a timing gun to approximately 20 degrees whether-or-not you have a Sunny or Pulsar. You will also notice that almost all low-load areas are identical to the Pulsar GTiR timing map, even up to the engine load column (54). However, once you move into higher engine loads (i.e. load columns 54-86) you will see that the Sunny GTiR timing map makes the timing a lot more retarded (i.e. closer to TDC) compared with the Pulsar GTiR timing map. You can see that during the on-boost RPM at high loads (i.e. 4050 RPM and load 86) the Sunny GTiR ignition timing is 9 degrees BTDC! This is few degrees more retardation than the Pulsar GTiR timing map, resulting in much more protection against knock/pinking, but at the expense of reduced power/torque. By looking at both the fuel and timing maps, you'll be able to see that the Sunny GTiR maps overfuel and retard ignition timing when compared to their Pulsar GTiR counterparts. Perhaps this was done to combat lower octane fuel found in Europe, but it unfortunately results in grossly conservative fuel/timing maps.
I hope this helps to shine a little information on the standard Sunny/Pulsar GTiR fuel+timing maps.
Last edited by watoga on 23rd October 2013, 8:30 am; edited 1 time in total