Can someone explain trigger angle?
 

so...I got a MSPNP for my miata and I'm at the point where I need to set base timing. It's telling me to adjust the "trigger angle" but I'm a little confused about what that really means.

Does this simply mean that I'm telling the computer that the cam is approcahing TDC earlier/later than it is so that it will in turn adjust ignition timing?

I guess what i really want to know is: what am I changing/affecting when I adjust trigger angle?

I could just go in there blindly and messing w/ values but I want to have a complete udnerstanding of what's going on.

thanks!

Trigger angle is the angle before TDC where the Megasquirt "thinks" it's getting a signal from the CAS. If you have a trigger angle of 60 degrees and a spark advance of 20 degrees, for example, the Megasquirt waits for a signal from the CAS, then counts down the amount of time at your RPM it would take to turn 40 degrees, then commands it to fire a spark. If the CAS signal actually came in 65 degrees BTDC instead of 60 degrees BTDC, the spark would happen at 25 degrees when the Megasquirt "thinks" it's happening at 20.

So the goal there is to make the physical trigger angle match the angle that the Megasquirt is using to calculate its ignition timing.

So when you match the physical trigger angle and the angle that the megasquirt is using, the megasquirt no longer "thinks", but rather it "knows" the actual angle b/c everything is matched?

Kind of. MS has no way of verifying the actual position of the engine. It never knows the actual angle, the assumption is that they match, even if they don't. If any of the triggering components would change position the MS would never catch on.

This doesn't specifically cover the technical background of what exactly trigger angle is, but Matt's already done that now, but check out this video for hints on setting up your base timing with your MSPNP MM9093 (or any MS1 Extra car).

http://www.megasquirtpnp.com/models/...#Section_Seven