Perfect Power Application Notes.


Application Note : AN 1


The SMT8-C was optimized for CAM modifications and as such can tune the CRANK and 4 CAM signals. This is required if extensive engine modifications are done, or if a smooth idling engine is not required, or when the CAM shift point should be moved. This application note does not explain why the CAM timing should be changed, but how to change it. In most cases the CAM timing is changed after the installation of a supercharger or turbo.

CRANK and CAM TIMING Background

In most high performance engines the CAM timing is adjusted by the ECU to give a very smooth idle performance and perfect emission. Once the engine goes in to medium to high power it runs smooth automatically and the ECU adjusts the CAM timing to a setting more suitable for power. The adjustment is gradually so that no one notices it. However, you can see the CAM change on the DYNO graph.
The ECU changes the CAM timing via a PWM signal, which operates an oil pressure solenoid, which turns the CAM in respect to the CRANK. In older engines this is done fast, but more modern engines do it gradually. In order to perform this gradual change, and to drive the CA< to the desired position, a feedback sensor is mounted on the CAM, which tells the ECU in which position the CAM is. This is the signal the SMT8-C will modify. More about this later!
A "V" engine with two overhead CAM's on each bank has four independent CAM circuits and four "feedback" position sensors. This is matched by the SMT8-C. However, for modification (mapping) ease the two inlet circuits are modified by ONE map value. In essence the SMT8-C has one exhaust CAM map, which feeds two exhaust modification circuits. This is duplicated for the inlet CAM's.

Technical Considerations

The SMT8-C does not work with ABSOLUTE crank/CAM angles but with differences or modifications. It requires the crank signal as a reference and retard/advances the CAM signals accordingly. Of course, it can also modify the crank signal for ignition timing.

The CAM's are linked to the crank. A much better way to put it is : The CAM's are driven by the ECU to a position signaled by the crank signal. If you are modifying the crank signal to affect the ignition timing, then the CAM timing is affected adversely. Let's assume you ADVANCE the ignition by lets say 3 degrees and you like to maintain the CAM timing. Then you need to RETARD both CAM's by 3 degrees. I am not sure that you notice 3 degree CAM timing, but the point is made.

Of course you can change the CAM timing to any point you like, as long as you consider that the ECU is changing it as well. The following diagram explains it :


SMT8-T Piggy-Back Unit - CAM Modifications



It is practical to make an approximate sketch of your particular engine CAM behavior and your desired CAM timing for the exhaust and inlet CAM's and then punch in the numbers in the respective maps.



Very Technical

The following diagram shows how everything fits together.


SMT8-C Piggy-Back Unit - CAM Modifications



The CAM inputs have in internal pull-up to +5V and are optimized for 2.5V trigger level. The CAM map entry is in degrees. Positive entries advance, negative entries retard.

An engine with SMT8-C CAM tuning without ignition tuning looks like :




SMT8-C Piggy-Back Unit - CAM Modifications