when timing is changed to say 16*.....does it inject fuel sooner or later than stock

 

sooner, you will be injecting fuel 16* before top dead center

 

thats what i thought wasn't for sure though.... Thanks

 

Additionally, the spray cone of the injector will be wider as it injects sooner. That also plays in with injectors with the 145* or 155* spray pattern. With a cupped piston dome, the spray needs to be inside the cup not washing down the walls of the cylinder. Getting the spray to just the right spot helps make power and changes burn tendencies. As timing is set closer to 5*, you almost get a stream effect instead of a cone.

Boosting timing to high levels (above 16* in this case) is probably not needed or condusive to making power unless or until the rpms of the engine are turned up past 4000, then, like any engine, the fuel needs to hit the cylinder on time for the piston to travel to the top of the stroke so it can light at the right time and drive the piston back down.

 

Timing does not affect the angle of spray.

 

Nope -- you are right. That is controlled by the angle of the holes. But timing does effect the width of the cone as it strikes the piston bowl. The closer the piston when the injector pops, the narrower the cone, even though the angles remain constant. Get timing too far advanced for the FPS speed of the piston and you end up spraying the cylinder walls instead of the piston bowl -- partly why there are some issues in running marine injectors with the 155* spray pattern.

Fogrive my ultra-crude Paint drawing, but it should help to illustrate.

 

This is also true, but at higher rpm the increase in timing will help to keep the fuel in the bowl.

 

Yup. When things start to happen faster, you have to advance to get everything "done" on time in the firing cycle, but with our low rpm engines, that point comes much lower in the advance scale than it might with an 8000 rpm gas motor (plus all the issues involved with a direct-fire diesel versus a spark-ignited gas mixture that complicate the issue somewhat).