turnin up the pump

[dahowerig]

hey guys. when i turn up the pump, it increases the fuel pressure i can only assume. so, therefore, i would want to put in my fuel pressure gauge and see what it is stock, and then go up from there, correct? what is a safe pressure to go up to?

 

[RDusch]

Chris,

I've never put a pressure gage on mine but i can tell you if your running stock injectors 1 turn in on the fuel screw is all you'll want to do, any more runs good but really takes it's toll on the pump.



If you want a lot more fuel you need bigger injectors to be safe.



Rick

 

[backroad]

Am I to assume that if you have bigger than stock injectors that it's then OK to go further than one turn on the fuel screw and not be hard on the pump?

 

[RDusch]

I've got over 100K on this pump with the fuel screw at 2 turns in or 1 turn back from bottoming out, this pump still pulls strong at mid and top but is starting to run rough at idle, i'm in the process of installing a new pump now the last one was a rebuild that i killed once before with stock injectors and to much fuel screw, it ran good for about 30K then broke the cam plate and rollers,

anything that you run cranked past stock is probably going to shorten its life some, but all the fun is worth a grand every 100K or better... ... ... ... . Rick

 

[formula]

ChrisHowe,



When you're talking about fuel pressure, I'd assume you mean fuel supply pressure? If so, then turning up the pump will only serve to reduce fuel supply pressure. But only at the point where you exceed the fuel delivery in stock form. (i. e. at idle and part throttle, you won't see a difference in fuel pressure even though the pump is turned up) A pressure gauge would still be useful in this case to make sure you don't have too little pressure.



As mentioned in the previous posts, the consequence of turning up the pump is possible increased wear on the high pressure pumping mechanism as a result of the increased pressure needed to deliver the larger volume of fuel. As far as I know, there is no practical way to measure this pressure. It is in the order of 8000 to 10,000psi or so.



Cheers,

Sean

 

[BushWakr - RIP]

When it comes to the "internal pressure" issue there are a couple things to make note of... . BTW, please, correct me if I'm off base here guys...



The lift pump provides rougly 7-8 psi to the low pressure side of the injection pump, or what is called the ''supply side". This pressure can range as high as 100 psi... perhaps slightly more.

This pressure in turn, detemines the max pressures generated by the high pressure side (head). As RPM goes up, so does the internal pressure on the supply side, and consequently the high pressure side as well. That's why the delivery valves, plunger etc are a matched/tuned component.

The uprated injectors often have a higher pop-off pressure than "stock" injectors. For example you may have a stock set that has 240-245 bar pop pressure... . when you uprate, they may have a pop pressure of 250-260 bar (3675 - 3822 psi).

The best I can determine, the lowest pressure you will see on the high pressure end, (kinda confusing) is roughly 4000-4500 psi or 272 - 306 bar.

From this you can see that the lowest pressures of the VE's 'high pressure side' can adequately supply enough pressure to run the larger injectors.

Now, when you run the pumps up in RPM, and you also increase the fuel demand (made by the larger injector) your (high) pressure increases to as much as 8,500 - 10,000 psi which is more than ample as well. It is sufficient in terms of supply pressure needed to provide the 'volume' required but, it is a bit weak on the ability to have a good health spray cloud like the P-Pumps do.



What is not adequately compensated for is... . injection timing. The fuel is injected later and later in the piston stroke as the pop pressure rises. This effectively "retards" you timing.

To compensate you advance the pump timing. . actually the start of the injection cycle so that injection start/stop, and the burn is happening at a more effeicient time in the piston stroke.



One pressure that does take a pretty healthy jump is the CYLINDER PRESSURES... these can take some healthy jumps if the injection pump timing is advanced too much.

For example, if you have your idle timing (my description) set to, say, 16*advance, then you crank up the high idle (governed speed) RPM with it's attendant internal pressure increase you can quickly have a total WOT timing that is very high. I believe that the "timing" advance can be as much as 2. 5 - 3. 0 degrees advance (or perhaps more). So consider your timing at 16* advance, then add the jump due to WOT/pressure related advance and you can see that it is quickly getting "way up there".



As an example, the KSB solenoid which temporarly advances pump timing during cold weather can alter the internal supply side pressure from a standard 4 bar to as much as 8 bar... that's a jump from roughly 58 psi to as high as 116 psi. This is done at the idle stage so you have a noticably better, slightly higher idle, and less smoke at startup.



The recent article in the last TDR mag has some confirming info on this as posted by Joe Donnelly. Give it a good read... . by the way, the turbo article is a good one too... . I particularly like the info regarding EGT benefits as they relate to 16cm and 18. 5cm housings.



Caveat: I don't have my Bosch manual here to double check the pressure figures so I'll ask for a bit of allowance on the figures mentioned above... as for any mistakes, my apologies in advance.



Pastor Bob.