Originally Posted by tomnik

Hi,

let me try to summarise:

stock engine, injectors, good overall condition:

Timing is a compromise: low emission, low noise level. Therefore the combustion pressure peak is somewhere well after TDC.
Regardless emission (this is not necessarily smoke but rather some components) and noise (typical diesel noise, not hard knocking) this combustion pressure peak is preferably just a bit after TDC.

Imagine the cylinder pressure curve over crankshaft angle.
What pushes the piston downwards is the area below the cylinder pressure curve but only the part that is after TDC. Part of this area before TDC means that combustion pressure pushes against the upward moving piston - no good.
On the other hand: Too late combustion pressure peak in relation to crankshaft angle will cause smoke and higher temperatures due to incomplete
burning because of decreasing pressure and temperature in the cylinder and not enough time until BTDC.

Now back to injectors:

No matter when you start injection the essential question is when or where is your combustion pressure peak.
Basically this depends on the ignition delay.
Ignition delay depends on the following:

- temperature in the combustion chamber (higher temps - less delay)
- droplet size or atomisation of the fuel (smaller droplets - less delay but against this: smaller droplets - kind of cooling effect of cylinder temperature)
and maybe some other things...

Temperature in the combustion chamber itself depends on engine condition (compression), rpm as the temperature drop is less at higher rpm (less time for cooling down).

Droplet size depends on:
- nozzles
- elements (actually fuel flow through the nozzles)
- fuel viscosity

In your case the higher pop pressure first delays start of injection and (assuming that the nozzles then atomise better) cool down the temperature (also delays start of ignition) but better atomised fuel burns faster.
All this combined with your engine condition it is impossible to tell you the best timing.


Combustion peak pressure before TDC will knock heavily, so again:
Advance until you reach this and go back 1-2 deg on a warm engine and test drive though all rpm range. The most obvious rpm range for knocking is idle and 1500-2500/min.


The accuracy of your locking tool is only as good as the guy who fixed the fly weights on your IP cam shaft!

Tom