Forgive me guys for re-writing a Bosch manual, or sounding condescending, but here's the big difference with the whole timing issue.
First, the faster the engine is running, the less time there is to get the fuel burned before the exhaust stroke starts. So as the engine speed increases, the timing should increase to maintain max power.
The VE pump does this by means of a piston connected to the roller ring. As supply pump pressure increases with speed, the piston is moved against a spring, rotating the roller ring and therefore advancing the start of injection, or PORT CLOSURE. Remember that term, there's a test later.:grinpimp:
The KSB (German acronym for cold start advance) does it by jacking up the pressure to the timing piston when the engine is cold.
On the P and A pumps, the timing is fixed due to the HELIX of the pumping plunger. Bear with me on this one. The in lines have plungers and barrels (P&B's) that pressurise the fuel. The barrels have what's called a fill/spill port. This is where the fuel enters the P&B to get pushed on to the injectors. The Plunger doesn't start pumping until it rises high enough to close this port. This event is referred to as PORT CLOSURE. Kind of like the way a two stroke engine runs. Now, we need a way to limit the amount of fuel delivered per stroke. Enter THE HELIX. The Helix is nothing more than a Helical cut from the head of the plunger partially down the plunger. Think barber pole. So, if we rotate the plunger within the barrel, we change the orientation of the helix to the fill/spill port. If we want max fuel, we keep the helix away from the port as long as possible to get the max fuel. For Idling, we simply rotate the plunger the other way, thereby moving the helix closer to the port. As soon as the helix starts to pass the port, all of the high pressure fuel above the plunger head has an escape path through the helix and back out the port, thereby ending injection.
Now, go grab a beer, cause it's about to get deep.
There are upper helices, lower helices, and upper and lower helices.
Upper helices will vary the start of injection because The helix is what closes the port, not the actual plunger head. The amount of fuel delivered is also varied because the further the plunger moves before Port Closure, the less plunger travel there is to actually inject the fuel.
With a lower helix, the port closure or beginning of injection is fixed because the plunger head is what closes the port, but the end of injection is varied. These are the types of plungers that are used in the P pump As well as the overwhelming majority of A pumps for Cummins applications.
And finally, the upper and lower helix. The upper helix controls the start of injection, and the lower helix controls the end of injection.
So what does it all mean? All other things being equal, the VE pump should start a little easier, and get a little better fuel economy. So for max economy, the VE should be a little better pump. The inline pumps, especially the P pump, are better for max power.
The VE pump has the handicap of having only one pumping plunger. You can only get so much fuel into the plunger to be delivered in a 1/4 turn at 1500 rpm.
The inlines however, get a full turn of the camshaft to refill and prepare to repump. So they can deliver a larger quantity of fuel.
Sorry for the 200 page novel. Hope this helps with some of the questions floating around.
Later,
SS