Right then
I've made a start on the calibration guides. I am part of the way through the ignition timing one, and will post it properly when its finished. In the meantime, a shortened version to get you going.
The first thing you need to do (I assume you have) is to set up the trigger and reference properly. That means when the laptop says 0deg for ignition timing, the spark is firing at TDC. To do this you will need a clearly visible TDC mark on the front pulley and a timing light - preferably one with an adjustable advance so that you can run the engine at a sensible ignition advance, but if not then you will need to set the ignition to 0 deg. You may need to hold the revs up a bit, depending on how well your engine runs with the ignition retarded this much.
Once you have got the reference settings dialled in correctly, then you know where you stand. This is where it gets difficult. The problem with calibrating ignition advance is that there is no convenient in car sensor that you can buy (like a wideband lambda sensor and EGT gauge for fuelling) that allows you to measure if its right or wrong. Also complicating things further is the issue of MBT or detonation limited ignition timing. Ironically, its the det limited region thats easier to set up. Some method of hearing/seeing det (det cans, knock sensor and scope/sound card etc) and you can actually find the ignition limit driving on the road (though I wouldn't recommend it - I'll come to that in a minute). However, you cannot find MBT without some kind of external torque measuring device - a braked rolling road or engine dyno in fact (well, thats not quite true, but the other methods for finding MBT are too expensive to mention here, so dyno it is
The easiest way to get up and running is to swipe a map from someone else with a similar spec engine. If this has been mapped reasonably well, then it may be a good starting point for your engine too. For all engines, similar means using the same fuel type (95RON or 98RON can make up to 6 degrees difference to mapped ignition). When using a MAF based system, a similar engine means same MAF meter. When using MAP or TPS system, similar engine means (at least) similar capacity, similar compression ratio, similar cams and similar exhaust backpressure. This is because the ignition timing relies on Air mass flow, so the conversion from manifold pressure or TPS to air mass flow will depend on your engine spec - i.e. the things listed above.
So a note of caution.
WHEN COPYING AN IGNITION MAP FROM ANOTHER ENGINE BE CAREFUL! If your engine flows better than the donor map engine then you will be getting a higher load for a given manifold pressure.
THIS COULD LEAD TO YOU DAMAGING YOUR ENGINE If you are not extremely careful to listen for detonation.
Now you have something that runs (maybe even seems OK) its time to head off to the dyno. In order to calibrate the ignition map you need to perform spark sweeps (or loops) at fixed speed and load point. This is why you need a braked dyno e.g dyno dynamics, not an inertia type, as it will hold the engine to a fixed speed regardless of how much load (MAF, MAP or TPS are your load measurement) you put on the engine. You will also find it useful to have some kind of adjustable throttle stop (or stops) - little blocks of wood of different sizes will do - that allow you to easily hold a fixed throttle position. Once you have the car running at a fixed speed/load (start at low speed and load as its safest for the engine and will give you a feel for whats happening), you then need to sweep the ignition in 2 degree steps and record the torque figure achieved at each value of advance. The ignition advance that gives you the highest torque is TRUE MBT. You will notice (if you plot the data) that the curve is very flat at light loads. MBT is
Minimum ignition for Best Torque - i.e. it is on the retarded side of the curve. So standard practice is to then set the map value to slighly retarded of true MBT, e.g. the point at which the torque has dropped by 0.5% from peak when plotted.
Follow this process and slowly fill in the map from low speed low load working diagonally up the speed and load axes. You don't have to do every point, but since there aren't that many sites in VEMS (which is a
good thing), it wouldn't take too long if you did. Your biggest problem will be aligning your data with your axis breakpoints - if you are using the 'blocks of wood' throttle stops you may need to do some interpolation (smoothing) of the data points. Excel is good for this.
At some stage you are likely to become det limited, i.e. the engine will begin to knock. Remember you need to have a knock detection system in place
before you get to this point. This is most likely at low speed/high load sites, and then will decrease in strength as you increase the speed. For an engine without active knock control, I would recommend setting the ignition map to BLD - 3 degrees. BLD = Border Line Detonation, i.e. when you can hear knock occuring and a rate of 2 'pings' per second or more. So whatever ignition advance this occurs at, take 3 deg off this and enter that into the map.
Another word of warning.
DETONATION IS SENSITIVE TO INLET TEMPERATURE. If you map the engine when the air is cold (i.e. in the winter) you will find it is too advanced (in the det limited region - MBT is unaffected) when the air temps get hot. If you are not using any inlet air temperature correction (which should be around 1deg retard for every 10deg increase in inlet air temp) then
BE VERY CAREFUL. Turbo engines are even worse for this, particularly when people just turn up the boost and start to run off the end of the compressor map, which introduces
a lot more heat to the inlet air.
So, at the end of a day on the rolling road (or maybe less if you're quick / exprienced) you should have an ignition map, and by association a fuel map (since you will have needed to be adjusting the fuel throughout in order to get the best torque / keep the EGT's at a sensible temperature). Now you can look at driveability, but we'll cover that another time maybe......
Oh and BTW, 0.88 lambda is more than
a little rich. Its about the lambda for peak torque. To give a rough scale, 0.98 is a little rich. 0.95 is slightly rich, but good for driveability. 0.9 is quite rich. 0.86 is about peak torque rich for WOT. 0.8 is overfuelling for EGT's rich, 0.75 is overfuelling quite a lot for EGT's rich, and 0.7 or richer is black smoke 'I've got too high a compression ratio and i'm running massively retarded and then overfuelling ridiculously to keep the EGT's in check' rich.
Have fun
