Ok. I agree with that, but how do you know your timing light is telling you the correct number.
I've personally seen timing lights that are 3-4 degrees fast, and some that are 3-4 degrees slow. That's a big spread.
I never get excited about what the final number is. I don't care if your timing light says you have 30 degrees as long as the plug says that's all it will take.
Same with the other way. Of your timing light says 40 degrees total is what the plug says you need, that's where you time it.
Timing lights are a tool and they almost never read exactly alike. That's why I tell everyone to use the same timing light, every time.
