When do the injectors fire?

[Begle1]

Where, in relation to TDC, do the injectors fire on a stock truck?

How much of a degree-difference does the VE's automatic advance result in?

How much of a difference does moving the pump generate?


Where do P-pump'd trucks fire?

[KTA]

Stock it is like 8deg, and full advance is about 15deg. P-pump trucks were stock anywhere from 9 to 16 depending on the CPL and the marine 370 is about 22deg.

[Begle1]

So it starts 8 degrees before top dead center, and then advances all the way to 15 degrees?

How bad would it be if one were to set it right on TDC?

[wannadiesel]

Very bad white smoke, would misfire at high RPM.

[Begle1]

What if one were to fumigate massive quantities of propane or methanol into an engine timed at balls-on TDC?

Wouldn't the timing eliminate any chance of pre-ignition or timing knock and allow the fumigated fuel to be utilized to the maximum?

Think it'd be effective?

[wannadiesel]

It would still light too early, and then you'd have fuel delivery problems due to insufficient injection pressure.

[Begle1]

It would still light too early, and then you'd have fuel delivery problems due to insufficient injection pressure.

Do you know how hot the cylinders get during compression stroke, before the fuel is injected? If I were to fumigate propane into an engine with no injection pump, while cranking the engine over, would the propane light off?


You're saying that, since the cylinder is under more pressure at TDC than at 15 degrees before TDC, then it will be harder for the injector to push the fuel into the environment?
Think that effect would really be noticeable?

[wannadiesel]

It's hard to say what the exact temp in the cylinder is, it varies depending on engine temp, air temp, load, RPM, boost, etc. It's generally over 600 degrees in there right before the fuel gets sprayed.

I'm saying that the pressure from the propane lighting off would cause you to need more injection pressure.