injector pop pressure vs timing advance

[YOUNG GUNS15]

Haven't seen it brought up yet but there is 'line pressure' in the injector lines that would lessen the amount of timing retard on higher pop pressure injectors if all your using is final pop pressure and a 0-300 bar scenario (assuming the pump has to create that pressure from nothing, when actually there is residue pressure in the line that aides pop pressure. . On a typical PLN (pump line nozzle) I was told it is around 300psi left in the line, this is from school so my information might be off since its been two years since we covered this.

 

[straight 6 roar]

But the injection pressure of for example P-pump is 1000+ bar, unit injectors around 2000 bar and latest high pressure commonrails close to 3000 bar.

Yes I don't think the difference between 280 bar and 300 for vp pop would matter much for the start of injection. Maybe 1* of timing lost. After the injector pops the gig is up, the VP might have a slightly higher peak pressure but nothing a p7100 injector won't handle considering many run them with 13mm plungers(faster rate = higher psi).

Everything is compressible. The part that people omit when talking about liquids is that they are VIRTUALLY incompressible. Day to day usage, the amount they compress is so slight that they don't need to be accounted for. But it is there.

When you start talking 300, 600, 1000 bar it makes a bit of a difference. If the contained fuel volume in the line drops 3%, that's 3% more volume the plunger must sweep to get to that pressure. Small difference but that equates to a few degrees of crank rotation as I was told by a very knowledgeable source.

Things get real weird when you step up to big lines and big injector feed passages. A small line has say 5 cc's in it which compresses 3% before popping. That is .15 cc's the plunger has to stroke before any fuel has expelled. Step up to a .120 line, now your line has 10 cc's in it, 3% compression before pop is .3 cc's the plunger has to stroke before anything pops. More cc's to stroke before pop = more degrees of crank rotation. I used fairly arbitrary numbers but many top builders will agree that it does make enough difference to account for in a performance application. I personally think the bizarre lopey idle that comes from bigger lines and tubes is not a phenomena of injection delay but how the line comes up and down in pressure from this increased volume cushion.

 

[dieselbeef]

that's a well thought out conclusion...I dealt with the idle issue tho. with stock lines and just the filters out of the nozzles. undriveable. altho when I went from the sac type inj to the vco it stopped. either with or without the filters.

now back to our regularly scheduled discussion about flow vs timing retardation...

 

[Tate]

When you start talking 300, 600, 1000 bar it makes a bit of a difference. If the contained fuel volume in the line drops 3%, that's 3% more volume the plunger must sweep to get to that pressure. Small difference but that equates to a few degrees of crank rotation as I was told by a very knowledgeable source.

Things get real weird when you step up to big lines and big injector feed passages. A small line has say 5 cc's in it which compresses 3% before popping. That is .15 cc's the plunger has to stroke before any fuel has expelled. Step up to a .120 line, now your line has 10 cc's in it, 3% compression before pop is .3 cc's the plunger has to stroke before anything pops. More cc's to stroke before pop = more degrees of crank rotation. I used fairly arbitrary numbers but many top builders will agree that it does make enough difference to account for in a performance application. I personally think the bizarre lopey idle that comes from bigger lines and tubes is not a phenomena of injection delay but how the line comes up and down in pressure from this increased volume cushion.

Couple the fact that the bigger lines have a thinner wall (they usually have the same OD), so they will expand even more than a factory line. Just compounds the problem.