wrd1972

How does the optispark advance or retard the timing.
Are there mechanical mechanisms that do this, none of which I have seen.
Just wondering how timing adjustments are made in the distributer.

'94 Bad A Z28

It doesn't...

Injuneer

All the Opti does is tell the PCM where the cam is in its rotation. Timing is set by tables in the PCM, as a function of RPM and engine load (MAP). Timing can be adjusted with various offsets, e.g. for inlet air temps, and will also be altered based on the feedback from the knock sensor. Once the Opti tells the PCM where the cam (and hence, the crank) is, it has no affect on timing.

wrd1972

I guess I still dont understand.
So if the engine knock sensor hears knocking what is actually being retarded?
How is the timing physically being adjusted or tweaked?

sw89lt1

the computer tells it when to fire. if the knock sensors see knock then the computer will send the pulse to fire later. their for retarding timing

NoRegrets78

The new MSD opti will give you +/- 5 degrees timing adjustment by I'm guessing tricking the PCM. If you want to manually adjust timing and have a solid opti, I'm thinking this is the way to go.

1racerdude

Ya change timing IN THE COMPUTER. End of subject. You have to get a tunner like Madwolf or PCMForless to change it or have the equipment to do it yourself.
If ya want to buy a 2000 dollar Fast system,that's different.

Injuneer

No, the "adjustment" in the MSD Opti is not for the purpose of changing ignition timing. It's there to allow you to advance or retard the cam to alter the power curve.

Because the Opti is driven off the nose of the cam, advancing or retarding the cam (relative to the crank) screws up the ignition timing, because the Opti is indexed to the nose of the cam. You would have to go into the timing tables in the PCM and offset the entire timing table by the amount you advanced or retarded the cam. With the MSD, it appears to allow you to compensate for the cam advance/retard by altering the position of the Opti optical sensor relative to the cam nose.

TransAm-Z

Could you get the same effect by modifing the Opti-Unit to be rotated? (ie slotting the bolt holes and using some type of offset dowel bushing for location) There some reason that this would not work?

96capricemgr

You guys are missing the point. Move the whole opti and you just moved the WHOLE ignition curve rather than just the areas that may have needed tweaking. The PCM tuning allows such finer control of the curve. Either learn to accept the computer is where it is at or buy an old carbed car because fighting the computer rather than embracing it will get you frustration and a slow car.

Injuneer

Chill Dwayne... I think he was asking relative to the cam timing, not ignition timing.