Power gains from bigger fuel system?

[HiPerf360]

Is there any power to be had by upgrading the lift pump and lines? The low fuel pressure light on my FMS box comes on at 2psi (I think) and it is always on when I turn the power up. Any ideas would be appreciated.



You can see my mods in my sig.

 

[Todd T]

you should consider at LEAST Banjo bolts.



my preference would be to see you put on a helper pump at the tank.

 

[**ICEMAN**]

others may disagree,, but after adding my pusher and bj bolts i felt a increase in power due to the fact that now i am supplying enough fuel to feed what my powermax is asking for . before,,0psi @ wot,,now 10psi wot. so i'm saying yes to power gain but no to it being more than the box is advertised to put out.

 

[JR2]

There are alot of opnions out there on how low is too low. I think I would go with at least Banjo bolts and a pusher pump.



I moved my stock lift pump to the rear of the truck and added stainless steel fuel lines through out. With all the mods I have I can suck my press down to 4-5 psi at WOT. I am considering a different pump because I would like to see 8-9 at WOT.

 

[Todd T]

I think we all agree... . 0 is BAD [shrug]

 

[Bigsaint]

Jonathon, if you don't stumble at WOT you are okay, bottom line. Less psi's mean more volume, too a point. Think of it as the high psi's equaling a restriction, when you hammer the go pedal you are opening up that restriction and then the fuel volume is up and the psi's are low.



2 psi's is lower than what I would personally be comfortable with at WOT. I would either swap out those banjo bolts for a set of Ray T's bolts ( available at Genos) or replace them all together with Weber adapters and Aeroquip elbows, or choice. IMHO, you'll get the smoothest fuel flow with the Aeroquip elbows.



Remember too that you still have another restriction, the OEM fuel filter. I don't recall it's rated volume, but I don't think it's much more than 40-50 GPH and I plan on removing it completely and replacing it with a Racor 90 GPH filter/housing in the spring.



I have two FP gauges, pre-filter and post. It's interesting to watch both on a WOT run. The pre psi's never drop below 10, while the post filter psi's ( what the VP44 is actually seeing) can get as low as 5-6 initially, and then climb back to about 8 psi's during a sustained run. This is with very large injectors, the EZ box and the TST set on ' KILL'.



If you do nothing else, add a post filter fuel pressure gauge to watch those numbers, like Todd T. said, 0 is bad, way to close to a vacuum number for me.



Scott W.

 

[Roger rodbolt]

HiPerf360,



Larger lines and proper pressure will (IMO) boost horsepower with your setup. At your power level I'd delete the banjo bolts and run larger lines from the tank with a rear pump or rear/dual pump setup and -6AN lines to the filter and VP44 with high flow fittings. I intend to remove my forward -6 lines and install -8 lines with different filter setup. Have the parts to do it just need the time.



Also, the fuel pickup in your tank is restrictive.

 

[Mopar-muscle]

well heres my over rated 2 cents ...

i looked for a 90 gph filter , its a bit to big to get anywhere and have it accesible , to me anyway ... plus you aren't using 90gph , why do you need that flow ? if you have that much flow you better have a regulator screwed into the input of the VP44 ...



in my underrated opinion , if you get an increase from a fuel system upgrade you had a fuel supply problem to begin . as far as i have seen on this site NO ONE has any legitimate data to prove a performance increase ... NO ONE ...



i want someone to prove me wrong ... . all the claims of performance increase have been seat of the pants , its like the doctor giving you a pill to make you feel better and later you found out is a sugar pill and it worked ... its all in your head ... to justify the money you just spent ...

 

[HeberRam]

My $.04 worth!

I agree with Mopar... We did just that, increased line size and dynoed before and after... There was a couple of HP increase (3 to be exact) not what we considered mind blowing. In fact we took it in stride, had we done another Dyno pre-line increase we may have gotten the same results. My opinion is too much line pressure on the VP44 can be harmfull. How much I don't know? We all know 0 is no good, somewhere between a low of 3psi at WOT and at 15psi at idell is what I aim for. Best thing to do is install a fuel pressure gauge and monitor fuel pressures, just like you do with the pyro and boost. l

 

[LSMITH]

I have to disagree with one thing I have read on this subject. Lower pressure does not mean flow has gone up to anything but the injectors. Lower pressure means that the fuel that is being used is becoming nearer to equal the capacity of the lift pump to supply fuel. A reading of zero PSI means that the VP is using all of the fuel that it is being given, negative is more used than is given. The internals of the VP are a mystery to me at this point, but for cooling and lubrication you MUST have a positive pressure at the inlet to the pump. For me the ideal situation would be 15 PSI at idle and 15 PSI at WOT. To do that you would need a pump capable of filling the needs of the VP and also filling the return system with enough fuel to generate a 15 PSI "surplus" of fuel. It is obvious that a regulator is necessary to do this. I hope this helped to clear things up and I did not create confusion.



EDIT: it was confusing, hope it is fixed now.

 

[Un-Hemi]

Lsmith, that's the clearest explanation yet of what occurs in this fuel delivery system under load. Thanks!

 

[HiPerf360]

Has anyone tried to put a pressure regulator on the return and just set the pressure for about 8psi. ? This would require an aftermarket pump of course. Just an idea, what do you think?

 

[Steve Campbell]

Isn't there a pressure regulator in the outlet banjo bolt holding anything less than 14 psi inside the VP44? (I thought I read that in a post a year or so ago. )

 

[Un-Hemi]

Hiperf, Steve is correct. The bypass valve is acting as the system pressure regulator. If there isn't at least 10psi fuel pressure at the VP-44 inlet, that bypass valve is *CLOSED!*

 

[Patriot Diesel]

I can't really say whether there are power gains associated with an upgraded fuel supply system.



I can tell you this... with the current setup I have... lots of fuel being pushed through my BD IV's and the FMS on 50-63%... at WOT my pressure never has dropped below about 12 PSI... this is with the wonderful kit that Advanced Diesel Technology sells. It has a replacement lift pump and adds a pusher pump and braided fuel lines from the pusher all the way to the VP44. Andy or Doug can give you the more technical explanation of their system...



I love it...

 

[Mopar-muscle]

i agree , 0 psi is not good , and yes you are using all the fuel that is being supplied to the VP44 , a positive pressure is the best solution . how much ? who knows .



heber ram , that 3hp could be operator induced , still not hard data .



lsmith , yes i agree , its not an increase in flow , but pressure is the RESTRICTION to flow , and again yes , as the pressure drops it means you are using the fuel being supplied , increase pressure , you have more than enough flow if you go back and read the test results i got with the flow meter in the return line , as pressure dropped fuel returning to the tank increased , though we were able to increase fuel pressure from 0 to 5 psi , there was NO increase in fuel returning to the tank .



as far as your system , it could be done , i think you would need a 30psi lift pump and a regulator on the inlet to the VP44 , but still , if you have 15psi when you are demanding a high amount of fuel to begin with you still run the potential of lift pump damage from cavitation (???) ... but then again what do i know ...



tommy t , as far as the overflow valve on the VP44 , i have to believe it is for the internal low pressure pump within the VP44 , if not how do you or anyone else explain 20 to 30 psi claims at the inlet to the VP44 i have seen posted with the addition of a pusher pump ? if the overflow valve was for the inlet line it should not go above 15psi .

 

[Un-Hemi]

John, there is too much restriction in the overflow valve to bypass the amount of fuel being supplied to the VP-44 with the extra and/or larger lift pumps. The only way to pass more fuel through a given size orfice is with higher pressure. In the case of those who are generating greater than 15psi inlet fuel pressure, the overflow valve is overwhelmed. It's wide-open and can't cope with the available volume of fuel.



It's my belief that the overflow valve is fitted to the inlet chamber of the VP-44 and has nothing to do with the internal low-pressure pump. Has anyone actually taken a VP-44 apart to check this issue?

 

[HiPerf360]

What is the max amount of fuel a bombed Cummins can use? Knowing this I can design a fuel system to supply enough fuel at all times to keep a regulated pressure.

 

[Un-Hemi]

"Mike, thanks for the numbers! If the BSFC is . 4 lbs/bhp/hr at 3300 rpm, then at 215 hp, the engine is burning 86 lb/hr. That's 12. 28 gallons per hour. Diesel fuel weighs approximately 7 lb per gallon"



There ya go, Hiperf. That's copied from the "pumps, lines and whatnot" thread from some time ago. I suggest that if you haven't done so, read the entire thread. Carefully.



Pick your horsepower and calculate the fuel burn. Some additional fuel is recirculated to the tank from the injector manifold in the head.



This goes 'round and 'round & 'round.

 

[15w40]

I have recently found an interesting book that has answered many of my novice questions about diesel fuel injection and the endless discussion on fuel pressure with our ISB engines. I think many have assumed that more pressure is better. That may not be the case. Bear with me as I try to condense several pages of info into this post.



As everyone knows, the low-pressure fuel delivery starts at the fuel tank where the Lift Pump sucks diesel from the tank and delivers it to the fuel filter. (I think "sucks" is the appropriate word. ) From the fuel filter, the fuel enters the low-pressure stage of the distributor-pump, the VP44 in our trucks. The low-pressure vane-type pump is located around the injection pump's drive shaft. It goes on to explain how this is a conventional centrifugal pump with four vanes, larger, but not unlike the lift pump. A spring loaded pressure control valve sets the injection pump internal pressure. If fuel pressure increases beyond a given value, valve opens the return passage. If the fuel pressure is too low, the return passage is closed by the spring. This pressure-control valve is fitted to ensure that a defined injection pump interior pressure is maintained as a function of supply pump speed. Some fuel flows back to the fuel tank in order to provide cooling and self-venting for the injection pump. It goes on to say the vane-type supply pump is powerful enough to draw fuel out of the fuel tank and to build up sufficient pressure in the interior of the injection pump. In those cases in which the difference in height between the fuel tank and injection pump is excessive and (or) the fuel line between the tank and pump is too long, a pre-supply pump (lift pump) must be installed.



So what does this all mean? It sounds to me that as long as there is a positive pressure at the input port to the VP44, that is all that is needed and as you go up in HP there is an argument in favor of larger fuel lines and pusher pumps. High pressure from the lift pump may not be needed.



Nomex on.



By the way, if anyone is interested in the book, it is published by the SAE, titled: "Diesel Fuel Injection", ISBN: 1-56091-542-0. This was published in 1994 and has info on the Bosch P and V pumps, but not specifically the VP44.