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1. Part 1 Basic Speed Density tuning and LOAD calculation In this guide we will explain the basics of Speed Density (SD) tuning and then go further into detail. The basic level (Slope tuning) is probably enough for most tuners to get their vehicles set up to a high specification. In general if you have not really modified the vehicle heavily your speed density tables should be well set up by Ford and you may only be seeing areas outside the normal because of injector scaling being out. You should start with your injectors dialed in to a high level and they should be dialed in on a stock car where possible. Starting with factory injectors to dial the car in with the new mods will save a lot of time resolving injector scaling issues. A lot of high performance vehicles use injectors with good data supplied and tuning them often requires no changes to the Speed Density tables. Enough of a rant, lets get into it. Speed Density Calculations The sample vehicle is a factory turbocharged vehicle, therefore we will be using the Open IMRC SD tables. The SD systems calculates the amount of air mass entering the engine based on different sensor inputs. In a nutshell the calculation is: Air Mass = VE_CORRECTIONS * (MAP - MAP_0) / SLOPE Where: Air Mass is the mass of air injected into a single cylinder (AirCharge in Ford language) MAP is the Manifold Absolute Pressure measured from the Temperature/MAP Sensor (TMAP) MAP_0 is the calculated offset for the MAP sensor SLOPE is the calculated Slope VE_CORRECTIONS, Volumetric Efficiency corrections for the SD tables based on, but not limited to, Coolant and Intake temperatures The Calculated SLOPE and MAP_0 will be expanded further as we progress. Part 1 Basic Level Tuning or Basic level SLOPE tuning In order to make the VE_CORRECTIONS = 1.0 we will assume Ford Standard temperatures and pressures (FSTP): Barometric pressure of 29.921 inHg, intake temperature of 100F and Coolant temperature of 200F, yes all imperial measures! We will start with just a couple of the SD tables and this will suffice for quite a high level of tuning. In fact most tuners will only tune in the slope table as this will, generally, provide enough capability and allow tuning in a time allocated to tuning a vehicle. We will also be using the BF for our example (catch code 77DA) as it has the most modifiers to the SD tables (complexity/flexibility). Lets start with the two tables we will be using to tune SD: auF0056: This is the theoretical MAP value when AirCharge is zero. auF0061: This is the Slope of MAP per AirCharge value used in the speed density calculation Both of these tables take as their inputs RPM (x) and Intake Cam Angle (y). Immediately you will see you should log Intake Cam Angle/RPM/MAP to do analysis. Here are the two tables fro a stock calibration: Note the highlighted cells, we will be demonstrating the calculation for the Intake Cam angle of -10 degrees at 3000 RPM and a MAP reading of 50inHg (roughly 10psi of boost pressure). The calculation of the Air Mass will be: Air Mass = (50 - 2.7) / 19200 ~= 0.00246354 lb of air This will be of more use later but lets say at this RPM point on our dyno log we were commanding a lambda of 0.8 off the base fuel table and we actually read from the dyno wideband 0.82. In order to increase the calculated Air Mass in order to get extra fuel in we will need to reduce the Slope table as it is a divisor. You would do this by multiplying 19200 by desired lambda (0.8) / Actual (0.82) = 19200 * 0.8/0.82 ~=18732.0. You would repeat this process for each point in the rev range where the dyno wideband shows a difference between commanded lambda and actual lambda. If your Dyno does not log Cam Angle then all is not lost. You can use the following table to determine the theoretical cam angle for a given load: The highlighted cells are for when the car is on full load. So lets see which cells you would be modifying on a dyno run for the slope corrections. Here are this cells you would be modifying assuming you started your run from around 1600RPM: If you do have intake cam angle then pick the cells either side of the logged point. In the above example if the intake cam angle was logged as being 12 degrees at 5250 RPM then you would only need to alter the 10 and 20 degree cam angle points. In order to speed up the process you can delay tuning the SD tables and tune the base fuel table like a scratch pad. Here is the Base Fuel Table: So if our dyno runs shows variations in the commanded lambda to desired lambda or the following: then you can easily alter the SD cells in the SD tables for the RPM points 3000 -> 4000 to get the desired result. NOTE if you see something like this: Where B is the Wideband reading and A is the desired lambda from the Base Fuel table. This is a good indication your injector data is not correct and you could look at dividing your high slope by about 1.07. LOAD LOAD is calculated from the AirMass. The Basic formula for calculating LOAD is: LOAD = Air Mass / auF0008 (Airmass of a cylinder as sea level) So the LOAD from the above example with AirMass of 0.00246354 is 00246354/0.001723 or approximately 1.43 What happens to LOAD when I change the SD tables to get the commanded lambda? Say for example we had to alter the above example and increase fuel in this region because we altered cam shafts. So instead of 19200 we ended up with a quite big change like 16600 to get the commanded lambda. The new load would be: Air Mass = (50 - 2.7) / 16600 ~= 0.0028494 lb of air And the new LOAD would be 0.0028494 / 0.001723 ~= 1.65 You will need to take this into consideration when tuning the LOAD based tables such as spark. You can simplify this by using the new load will be 19200/16600 * old load. That is 19200/16600 * 1.43 = 1.65. This is assuming you have not changed the MAP at Zero value. It will quickly become apparent that if you are tuning the SD tables to resolve injector scaling issues you will end up with a very different load than what you expect and your timing could be substantially different to what you are expecting,. edit: The old summary thread can be found here for some more information including the full mathematical equation behind the model.
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