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Injector line size. When do we need bigger lines?


O6'er
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1206 fuel system.  The thread isn't about a high pressure injection system. I can believe 8% at that kind of pressure.  I'm not sure I believe 1% at 2400 PSI, but even if it is, it's not enough to affect timing intrusively.

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Just had a look at a Cummins 8.3 marine engine. (430hp) They have gone to a lot of trouble to get injector lines the same length. Also the same number of bends (although not in the same place)  on lower pressure systems timing effect would be very small but as pressure rises it would be more significant.  

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16 hours ago, dale560 said:

If you google it .this has been discussed here before or online someone had a formula for how much fuel compressed in a line because of microscopic air intrusion. Think it was on a tractor pull website. The answer was it was better to make lines different lengths than to have bends in each one causing parasitic friction and loss of flow volume.  

It would be nearly impossible not to have any bends in the lines. The ideal way would be to have the exact same length of each line and the same number of bends, but you just try to get the bends smooth and not put anymore bends than necessary. As long as the length of the lines are the same and there aren't any crazy bends, the pressure wave will propagate through each line in approximately the same amount of time, leading to equal timing and fuel distribution to each cylinder (of course this also assumes the injection pump is calibrated correctly). 

Of course the engine will still run if the lines are slightly different, but what you end up with is cylinders that aren't contributing evenly which can lead to timing/fuel knock or just less than ideal power from the engine. 

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Some engine injector lines are a real bundle of snakes!  
my 806 lines are odd lengths as the original RD pump seized solid (my fault. Forgot to drain water). It now has a CAV minims in-line on it. Runs fine although when I removed the exhaust manifold and measured exhaust gas temperature there is a bit of variation. Never caused a problem but not ideal. 

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Here is a little math for all.  Thinking about fuel delivery and timing, how many of us realize that at 2400 Engine RPM's each pistons is at TDC 40 times a second and fuel is being injected into each cylinder 20 times per second. 

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