Not sure if this belongs in the "advanced" section, but I ran a search in the LT1/LT4 section and didn't find too much that was useful . . .

A while back I installed the MSD optispark on my 97 Z28. I got sick of replacing the stock unit. I also have all the parts to convert over to the LTCC coil-on-cylinder setup, which I'd like to do. I'm wondering how the two of these systems will work together. Specifically, I'm concerned about timing:

The MSD opti allows timing to be adjusted with a set-screw +/- 7 degrees (might be more like 5 degrees, I'll have to look it up). I know that currently the timing is way off. I have a lumpy cam and some heads that put down 380rwhp on a mustang dyno (that was before my stock opti died). I took the thing to the drag strip with the new opti and it ran around a 14 @ 102mph. Based on what other guys were running at the track, I should have been able to do that when it was stock. Figure I'm losing around 100rwhp. Presumably this can be fixed by playing with set-screw. I'm a little nervous about doing this at the track for fear of blowing the motor by adjusting it too much in the wrong direction. An alternative might be a timing light, but since the PCM is clueless about what the opti is doing and I don't know what the timing is for the various idle tables in the PCM, I'm not sure how well this would work either.

The set-screw on the opti is a pain in the ***, since there is no obvious "zero" point. MSD says that "zero" is two turns out, which is what it was set at when I installed it. It has to be adjusted by hand and it's not especially clear that it will stay where you set it with all the vibrations. Something like lock-tite might interfere with whatever signal it is modifying, and I really have no idea what it would do if I took the set-screw out all together.

The LTCC coil-on-cylinder setup also allows timing to be adjusted manually (switches in their control box). The question I hope someone can help me with is this: if I install the LTCC setup with the MSD opti, does the opti still have to be adjusted correctly or will the LTCC module commandeer timing entirely?

 

If i were you I wouldnt change anything timing wise on any of those units. But yuo CAN verify timing with DataMaster and it will tell you what your timing is at any given rpm and load. I would use the computer to do all your timing changes.

 

I believe it's +/- 7*, and the instructions tell you to locktite the screw if it becomes loose.

 

I agree, also with the LTCC you have a couple different timing options on the box itself. Like built in progressive timing retarding for nitrous.

 

Will Datamaster recognize a timing change made with the screw on the MSD?

 

Couldn't agree more. I would have preferred that MSD produced an opti that just did what the computer told it to do. I don't actually want to manually adjust it. I had the computer dyno-tuned for a reason.

I'm not familiar with DataMaster. Guess I'll look it up. My problem is, even if it can tell me what the timing is at a given rpm/load, isn't it only telling me what the timing actually is (as modified by the adjustment on the opti) rather than what the computer thinks it should be?

 

PS: does anyone know what happens if the set-screw is simply removed?

 

The PCM isn't going to know anything about timing changes made after the spark module. It's just commanded spark, not actual spark. The best bet would be to mark or tape the damper and make a mark or pionter with the stock opti maybe at a couple different rpms no load, if possible, then set it to match with the aftermarket ignition. Then, at least, it should be pretty close.

 

When the MSD opti is advancing/retarding timing by changing the set-screw, is it modifying the signal that goes to the PCM from the optical sensor, or is it advancing/retarding the delivery of the spark itself after it receives a signal from the PCM to fire a particular cylinder?

If the MSD opti is itself advancing/retarding the delivery of the spark, and then I use the LTCC to commandeer delivery of the spark, it seems like it should not matter how the set screw is adjusted. The LTCC would deliver spark according to what the PCM tells it to do.

 

I have a Pro billet Opti but we havn't installed it yet.

The screw slides the optical pick-up forward and back inside the case. There is no electrcial minipulation of the signal, just a physical movement of the sensor.

The way it was explained to me was that the adjuster isn't really for tuning... it's to zero the timing at set up and later to adjust for some minor chain stretch. If you move it, you will be changing the PCM's input and output timings.

Zero the opti or it will influence your LTCC outputs aswell.

 

Should be obvious by now. It will move the full +/- 7*.

 

So it seems. Now that I am aware the adjustment is purely mechanical rather than electrical in nature.

 

No doubt about it. The only real solution is to fab up a good pointer, accurately mark TDC on the crank pully, and check actual timing with a dial back timing light. The reading should compare prefectly with Datamaster log. I have done this on my car to confirm timing and everything matches up within a degree. The biggest challange is to accurately find TDC. It's easy to do with a dial indicator with the head off. Its a bit more difficult with the head on but not un doable. I used methods typically used when degreeing a cam. Be careful because its real easy to miss TDC by a few degrees. You'd need to confirm your TDC a couple of times and make sure you measurements are repeatable. Take lots of extra time to make sure you have that nailed down before anything else.

Steve