Tuning

Cam Profile and Injector Timing

The Injector Timing table is derived from the camshaft profile. The intake and exhaust lobe events are what determine the time the injectors have to fire. The cam timing and the distributor PIP signal determine the degree in which the injectors fire. This degree is in reference to crank degrees. Understanding of cam profiles and crank degrees is necessary when tuning the Injector Timing table. The following is a brief explanation of cam profiles and crank degrees.

The crank degrees (0 - 720) are the total degrees it takes for one complete cycle of an individual cylinder. For example 0 - 180 degrees is the power stroke of the cylinder, while the 180-360 is the exhaust stroke and the 360-540 is the intake stroke, and last is the 540-720 degrees, which is the compression stroke. It is important to understand that the cam turns half as much as the crank. For every revolution of the crank, the cam will only turn half.

Most cam events are usually stated at 0.05 tappet lift, and are measured in degrees. Keep in mind that the degrees specified on a given cam card provided by the cam manufactures are in reference to cam degrees and not crank degrees. This 0.05 tappet lift is the universal standard which cam manufactures use so that end users such as you and I can compare different cam profiles. The total advertised duration is the total degrees in which the intake or exhaust is open. The duration @ 0.050 is the degrees that the intake or exhaust is open from the opening 0.050 to the closing 0.050. The open and close events are the points in which the valve opens or closes. Remember that these events are usually at .050 and are not the absolute opening or closing. The absolute opening and closing can be calculated based on the durations of each lobe ([total advertised duration - duration at .050] / 2 - Event). For example the stock Fox body Mustang cam has a duration of 210° at 0.050 lift and a total advertised duration of 266. This calculates out to ([266°-210°] /2 = 28°). Now you can take the 28° degrees and subtract it from the open event and add it to the close event. The intake open event for the same cam above is 371° and the absolute opening occurs at 371° - 28° = 343°. Keep in mind that not all cams have the same duration for intake and exhaust. This means the calculation will have to be done for both intake and exhaust.

Another thing to remember is while a vehicle is idling at low RPM’s the oil pressure that fills the hydraulic lifters is low. Thus at low RPM’s the lifters will collapse a little. How much they will collapse is dependent upon the oil pressure. When a lifter is dry it has about 0.200 clearances and when they are adjusted properly they are in the middle of that clearance. This means that the total possible collapse is .100 or less. After asking a few mechanics at Ford, they stated that there is a typical .030 - .050 acceptable lifter collapse clearance. Not all lifters have this clearance and some lifters have an anti pump up (check valve) built into the lifter. If this is the case then set the clearance to zero.

Now that the cam profile and crank degrees have been explained, the tuning can be explained. The optimal time to fire an injector is after the exhaust valve has completely closed and before the intake valve completely closes. If the cam profile has no overlap between the intake and exhaust then the intake open event should be used. Since almost all cams have some amount of overlap, the exhaust close event or the point at which the piston is TDC (360°) should be used. When the piston reaches TDC the exhaust flow has stopped and the piston will start on its way down causing vacuum. This vacuum is what causes the fuel to rush in the cylinder.

The mistake of firing an injector at the intake open event while the exhaust port may still be open will cause the injected fuel to be pushed out the exhaust or back up the intake runner. Again, this is if there is an overlap between the intake and exhaust before 360°. It is also important not to fire the injectors too late; otherwise, the injector will spray the back of the closed intake valve. Either of the two above conditions will cause poor fuel economy. With that said, the Exhaust close event (absolute) and the intake close event (absolute) are needed.

The same cam as stated above will be used as an example. Since the absolute Exhaust Close event happens at 378 and the absolute Intake Close event occurs at 609, which leaves 231° degrees to fire the injector. The injector pulse width is also needed. If the injector pulse width is longer in duration then the allowable injection time of 231° degrees then the injector need to be larger. For example if the engine RPM is at 6000 then (1000ms / [6000RPM / 60sec] = 10ms per RPM). Since 10ms represents crank revolutions, the time is doubled to represent cam time, which is 20ms. The 20ms then needs to be divided by 360° to get the time per degrees. We can then multiply this by the intake open degrees, which is 231° (20ms / 360° * 231° = 12.83 ms). We have now calculated the maximum time the injectors have to fire. This means that the injector PW has to be smaller than 12.83ms at 6000RPM or the injectors are too small.

Calculation

The currently loaded data log is used to determine the injector timing table when the calculate button is pressed. The calculations are based on the Exhaust close and Intake Open and Close events. If the injector pulse width is greater than the total allowable intake time dictated by the cam profile, then the calculation result will be marked in RED with a white background. This means that the injectors are too small to deliver the amount of fuel needed in the allotted time. If the data log does not contain any data for the current cell then it will be estimated. The estimation is done by averaging the four surround point. If four points are not available then the points that are available are used. The estimated values have a bold face type with a light Yellow background.

The calculate button in the cam profile section will calculate the intake and exhaust events along with the lobe separation. In order for this calculation to be successful the durations @ .050 lift and the lobe centers need to be accurate. If you enter in cam events manually and hit the calculate button, they will be overwritten if the calculated result are different then what you entered manually. If you know that your cam numbers are correct and do not want to have the EEC Analyzer calculate the results, then save your cam profile without hitting the calculate button.

Custom Cam

Custom cams can also be entered into the EEC Analyzer if you have the cam card. Cam manufactures will display the valve lift in either total lift or cam lift. Cam lift is the lift directly on the cam whereas the total lift is the lift at the valve including the rocker arm ratio. The EEC Analyzer has a default rocker arm ratio of 1.6 on the custom cam. If you cam card has the cam lift then simply multiply the cam lift by 1.6 and enter that value into the EEC Analyzer. If the cam card has total lift then you must know what the cam manufacture used to calculate the lift. For example, if you have a total lift of .545 and you have 1.8 rockers then you will divide the .545 by 1.8 to get the cam lift of .3027. Now multiply the cam lift .3027 by 1.6 to get the new total lift of .484. Enter ths value into the EEC Analyzer. When you save the cam profile in the EEC Analyzer you can then change the rocker arm ratio back to 1.8.

Injector Timing

This option is used to determine the edge of the injector pulse width that is used for the injector timing. The two options are Start (leading edge) or Stop (trailing edge). If you select the Start option, then the injector timing starts at the distributor PIP signal and ends at the leading edge of the injector pulse width. This is where the injectors will begin to fire. If you select the stop option, then the injector timing starts at the distributor PIP signal and ends at the trailing edge of the injector pulse width. The EEC will take the value in the injector timing table and subtract the PW converted to degrees to get the time when the injectors will begin firing.

Injector Firing Option
The selection for the injector firing will allow the user to select where the injectors will start / stop firing. The calculated result will be compensated for distributor advance/retard, cam advance/retard, lifter compensation, and injector delay. The user can select one of the following options:

Exh Close
With the trailing edge reference selected, the Exhaust Close event is where the injectors start firing and the injector timing table displays where the injector stops firing. With the leading edge reference selected, the Exhaust Close event is where the injectors stop firing and the injector timing table displays where the injector start firing.

Int Open
With the trailing edge reference selected, the Intake Open event is where the injectors start firing and the injector timing table displays where the injector stops firing. With the leading edge reference selected, the Intake Open event is where the injectors stop firing and the injector timing table displays where the injector start firing.

Max Lift
With the trailing edge reference selected, the Intake Max Lift event is where the injectors start firing and the injector timing table displays where the injector stops firing. With the leading edge reference selected, the Intake Max Lift event is where the injectors stop firing and the injector timing table displays where the injector start firing.

Int Close
With the trailing edge reference selected, the Intake Close event is where the injectors start firing and the injector timing table displays where the injector stops firing. With the leading edge reference selected, the Intake Close event is where the injectors stop firing and the injector timing table displays where the injector start firing.

TDC (Top Dead Center)
With the trailing edge reference selected, the TDC event is where the injectors start firing and the injector timing table displays where the injector stops firing. With the leading edge reference selected, the TDC event is where the injectors stop firing and the injector timing table displays where the injector start firing.

Custom
With the trailing edge reference selected, the custom degree entered is where the injectors start firing and the injector timing table displays where the injector stops firing. With the leading edge reference selected, the custom degree entered is where the injectors stop firing and the injector timing table displays where the injector start firing.

Note: These options are up to you, but the recommended option is the trailing edge and the intake open event if you have an A9L series EEC IV.

Corrections

The distributor timing will do nothing if it is left at 0 degrees in the EEC Analyzer. If the distributor is not set to the factory setting, note the difference in degrees. For example, if the distributor is set to 16 degrees before top dead center and the factory setting is 10 degrees before top dead center then the difference is 6 degrees advance. The EEC already compensates for the factory distributor setting therefore the only number the EEC Analyzer need is the difference. In the example above the EEC Analyzer should have a ‘-6’ entered into the distributor timing text box.

Note: Negative numbers are for degrees before top dead center (advance)
Positive numbers are for degrees after top dead center (retard)

The Injector Delay is the amount of time it takes the injectors to respond to the EEC’s commands. You can think of this as propagation delay or mechanical delay. Most injectors have about a 0.5ms delay. This delay is then calculated into cam degrees and subtracted from the injector-timing table. As the engine RPM changes so does the injector delay time in cam degrees. The injector delay time is a constant time, but when associated with cam degrees at a given RPM, the cam degrees for that Injector delay will vary from RPM to RPM. For example: If the injector delay is 1ms and one cam revolution takes 30ms (4000 RPM) the injector delay of 1ms would take 12 cam degrees. Now if the cam revolution takes 20ms (6000 RPM) then the same 1ms injector delay would take 18 degrees of the cam revolution.

Data Required
The required parameters for this calculation are defined in the “Calculation Requirements” help file on the settings tab.

Click to expand...

BooWFO said:

I strongly suggest, getting the xcal2 from a good tuning shop. That way it's right on the money for YOUR car.

Click to expand...