Well, I guess I can tell the engineers that I work for at Stanadyne that we can make all engine line lengths the same. Oh, and also tell my one customer who wants 18.3" lines and the other that wants 23.8" lines it doesn't matter what length to make them, even though they are both for the same DE10 four cylinder electronic pump).
If you cut inches off a line it WILL change timing. The lines are full of fuel while the engine is running and: for a given amount of fuel that is pumped, the same amount comes out the other end, which is Pascal's law. Changing the length doesn't effect HOW MUCH will be pumped, but HOW LONG it takes to get from one end of the pipe to the other.
If you looked at my pump at work while it's on the test stand, you will find pressure transducers on the discharge fitting of #1 cylinder on the pump (I will call it PE for pump end pressure), another on # 1 cylinder injector (I will call it NE, nozzle end pressure) and an instrumented # 1 injector which will show a trace of the needle being open (NL, which is short for needle lift).
There is a thing called line delay when dealing with a injection pump and its injectors. This is the time it takes for the fuel to enter the line at the pump and it to open the needle in the injector.
What I will do is measure the time it takes from PE to the time it takes for NL opening. This is measured on an oscilloscope in milliseconds. If you chop 3 inches off an injection line, your line delay has just gotten shorter (remember the lines are still fill with fluid and according to Pascal's law, the same amount will be displaced, but is this case, it just doesn't take as long to come out the other end).
An example: say it takes 15ms (milliseconds) from PE to the start of NL (needle lift) with 23.8" lines, it might only take 10ms using 18.3" lines. Why, because there is 5" of injection line now gone so it gets from the pump to the nozzle faster. Remember the line ID's are the same, so Pascal still holds true.
Sure it might seem like a lot, being only a few milliseconds, but it can add up to 5+ pump degrees in timing authority; that could lead you to be pumping over the nose of the cam, or on the base circle of the cam, both of which are bad.
This is why calibrating injection line lengths are specified by both SAE and ISO to be 25.5" long, with an ID of .0625".
Another point, by changing the line length, you can effect the afterwave going back through the line when the needle is shut. That can effect line pressures, just like changing line ID.
Do you want to debate changing line ID's?
And yes, that too makes a difference. Some of the different line ID's I've used for various customers while at Stanadyne (ID's in inches): .055, .0625, .067, .072, .093 and .098.
Changing the ID's will effect residual pressures which stay in the lines between pumping events. Typically, I will change other things to get the residual pressures I want first before changing line ID's. This again will require pressure transducers and an oscilloscope.
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