Bubba Z. said:Or at the very most a mail order tune. Just curious. A dyno tune is not always accesible and I'm wondering those who didn't get a dyno tune how your car runs. Thanks.
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.
Try Me said:I went to the dyno with my mailorder tune for mods in sig.
The mailorder tune was spot on - DaSilva could not improve on it without overstepping timing advance.
I know first hand, getting a mail order tune from MD.com is a safe bet.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?