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Engine mapping isn’t as easy as everyone thinks. Some engines are also more difficult than others. Standard engines are the easiest, especially if they don’t have variable valve timing. Being a good engine tuner is not something you become overnight. It takes time, the more engines you map the better you get at it. Every engine is different but also the same. Changing certain parameters will give you more power or will take power away. The basic symptoms are all the same and I will shortly touch on these.
What do you need to map an engine?
1.) First, you need a dyno.
There are a few things you need, the biggest one is dyno. You get 3 main types, and under these types, there are subcategories. The one type is you rolling road dyno that everyone knows:
You also get a hub dyno, these dyno’s get bolted straight to the car’s hubs. The dyno’s basically replaced the wheels on the car for the power run or mapping:
Most aftermarket ECU’s gets mapped on rolling road dyno’s as they are the easiest to work with. The third dyno that gets used is an engine dyno. These dynos are mounted on a testbed which the engine is also bolted on to. You have a lot more control over the engine and on big power engines, you don’t have to worry about a gearbox breaking. Here is a pic of a water brake engine dyno:
What is nice about an engine dyno is that the dyno reacts a lot faster than inertia dynos. This means if you make a change you will instantly see a difference in power. You can basically do live tuning. With the rolling road dyno’s you must make your change do a power run and compare to your previous run to see if it is better or worst.
2.) Measuring tools.
There are basically 3 main things you need, one is a Wideband lambda scanner so that you can measure the amount of oxygen in the exhaust. You also need a knock box, this a knock sensor you attach to the block of the engine. It works like a microphone. You wear a set of headphones that cancels out a lot of the outside noise and you can hear the engine from the inside. When an engine starts knocking you will hear it before the sound is audible at the engine. Finally, you need exhaust temp sensors. Ideally, you need one per cylinder as close as possible to the head. This is to monitor the exhaust gas temps, these tell you a lot about what the engine is doing.
3.) Sensor placement
It is very important where you place your Lambda sensor(s). There must not be any point in the exhaust that air can be pulled in before the lambda sensor. So if you have not clamped down slip joints, the sensor reading will be wrong and you will end up with a very rich map.
Like I have mentioned the exhaust gas prob need to be as close to the head as possible. The exhaust gas temp can drop quickly. The further the probe is from the head the colder the reading could be.
First thing you do.
If you start with a freshly installed aftermarket ECU, you need to play around with the maps to get the engine to start. Running too rich the engine won’t start and you will just wet the plugs. This makes it more difficult to get the engine started. Running to lead it will also not start. You can keep an eye on the lambda reading to see which way you need to take the fueling values to get it in range. For the first startup, the starting lambda value could be between Lambda 1 and 0.85. Lambda 1 is the perfect fuel to air ratio and Lambda 0.85 is to the rich side but not so rich that it will kill the spark plugs.
You can start with a timing map of 20 to 25 degrees right through the maps. This is a good starting point.
Basic mapping
Mapping an engine properly is a very time-consuming process. Most petrol engines are difficult to load up on a dyno below 2000 RPM. You can start mapping there. You set the dyno to 2000 RPM, the dyno will not allow the engine speed to go higher than 2000 RPM. At the lower sites, you want to achieve running Lambda 1. If you sit with a reading of let’s say 0.89, you would decrease the fueling value in small increments until you get to lambda 1. Now you open up the throttle slightly until you get to the next site on the map. You do the same thing again until you get to full throttle.
Most aftermarket ECU’s RPM range is adjustable. When it is set up you can have a map column every 1000 RPM or even every 500 RPM. You don’ have to map every column, you can do every 1000 RPM and then just interpolate between the columns. Then you can just do a sweep over the map to see if the lambda values look good over the complete map.
From 1/3 throttle upwards you can aim for lambda 0.95. Getting to 2/3 throttle you can aim for 0.9 to 0.85. When you are a bit more confined you can start to get the fueling a bit leaner. Most engines tend to make the most power in the range of lambda 0.92. For some engines, it is just not possible. Some engines are knock limited and others not. If an engine is knock limited, it will know before your timing reached optimum position.
Below 2000 RPM you must try and get to the sites you can map and map those points. With the map points you can reach you can look at the trends of the points around it and then put values in.
What to look for!
Always remember to keep an eye on the exhaust gas temps and listen for knock. If it Knocks at a site reduce the timing by 1 deg, if it still knocks reduce is some more. You will notice when you reduce timing the exhaust gas temp rises. You don’t want to let your exhaust gasses go hotter than 850 Deg C. Some race engines can go to 950 Deg C but you need to know what you do when you get that close to 1000 deg C. If a temp quickly run away don’t try and fix it close the throttle to remove the heat. You can melt a piston very quickly.
Ignition timing.
The easiest is to go to full throttle at an rpm site and increase timing. You will see the power increases until the engine starts making a knock or ping sound on the headphones. It will sound like static. Then you reduce the timing by 2 degrees at that point as a safety net. Now you move onto the next RPM site and do the same. You fill in all the timing below full throttle the same as at full throttle. Again you only have to do every 1000 RPM and interpolate between columns. On timing, you have to do a sweep on every RPM range to see that there isn’t a part in the map that there isn’t any knock caused by fast timing.
You do sometimes find a spot in the map that the engine does not like too much timing, you can lower the timing at that position and just smooth the map out so that you don’t sit with a sudden drop in timing. Sudden drops in timing cause hunting or uneven running.
Remember.
Mapping an engine is not a quick process, there are allot of factures that you must look at. I will discuss this in a later post.
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