Why are MFI fuel lines equal length?

[silverc4s]

I posted this question on Pelican a week ago, lots of input but no definitive answer. Thought someone here might have some knowledge to add:

I guess the obvious answer is related to the timing of fuel pulses at each cylinder.

BUT, if the lines are full of gasoline, a liquid, therefore non-compressible, the actual length if each pipe should not affect pulse timing, within reason of course.

Is it related to fuel volume in each pulse, or something more complex that I am missing completely??

I am asking because a non-Porsche friend, very knowledgeable in precise plumbing type matters (former machinist mate on a boomer), asked me, and I was not able to satisfy even myself with my reply.

Help!

THE PP LINK: http://forums.pelicanparts.com/showthread.php?t=378415

[ret9191]

I would guess that it has to do with pressure drop? Being in the HVAC business you always size pipe for pressure drop. If I remember every time you put in an elbow that equals 10 feet of pipe (depending on the radius) I am sure you would not want more fuel pressure/fuel going to one cylinder vs another. Make sense?

[silverc4s]

Yes, that does start to make sense, actually. Pressure drop differences = injector opening time differences, an unwanted phenomena, to be sure.

Question for you - Would a 90 deg bend in a steel pipe have the same effect as an elbow? Should all 6 fuel lines have the same degrees of bend??

Thanks for the answers.

[ret9191]

The pressure drop an elbow creates does vary depending on the type of elbow. An elbow is equal to a 90 bend. In HVAC piping a tight radius elbow equals twice as much equivalnt pipe length as does a large radius elbow. I guess I would try to use a tubing bender and make them all the same length or better yet copy a set from someone elses car? To prove my point of pipe length take a garden hose and fill up a bucket, time how long it takes to fill the bucket. Then add another piece of garden hose and then time how long it takes to fill the bucket. What you will find is it takes a lot more time, so would you want a different amount of fuel going to each cylinder? Hope that helps, if you need any further info I am out of knowledge please call Stuttgart or NASA. Thanks Ron

[robmog]

i think that elbow thing has to do with air movement not liquids.
to expound on the garden hose analogy, those new tightly coiled hoses
(like a phone cord) are 100% 360 degree loops, if a 90 degree elbow can
limit flow why does any water come out the end? i think if you timed the flow of two linked hoses vs one; the difference would be negligable.
an experiment is called for but its cold outside up here in the NE.
again i think this is an application of poiseuille's law
flow=(pi*R4th/8*n)*(delta P/L)
radius is the most important determinant (4th power); length is inversely porportion to flow
so length would have a small effect and curves probably none in a newtonian fluid.
FWIW
bob