Do you guys know what the max inlet pressure is for the VP44??? can you have too much??? If so, how much would be too much??

Thanks.

 

I've been told that above 19 psi you can get starting problems.

 

I was thinking more about damaging the VP44.....what pressure will be detrimental to its life??

 

Don't hold me to this but i've been told that over 35 psi could damage a vp44 over time. You could also call a local performance shop near you. Just a thought.

 

I've heard the same as Crazycumminskid.

 

Diesel Dynamics has TESTED to 60PSI and saw no icrease in power on the dyno.

19PSI is "press realease" max. I've been running 20-40PSI for quiet a long time, but my pressure is usually 20-28.

Merrick

 

Had my lift pump changed under warranty the other day and I was talking to the tech about this. He said that the pressure does not really matter. It is the flow to the VP44 that is important. This is what they have found, and why they changed the lift pump testing procedures.

Mike

 

Just a thought, then -- is it possible to put out good pressure on a gauge -- say 16-17 psi idle, 14 psi cruise, and 10-11 psi WOT, and yet not have enough flow to the VP? So that having a fuel pressure gauge means less than we thought?

 

That is a good question. Haven taken a hydraulics class in the past, pressure and flow do not have a direct correlation. It would seem to me that bigger lines would allow more flow at the same pressures. So it would be beneficial to have bigger lines.
Example.
If the pump operates at say 14#, or any pressure for that matter, If you doubled the size of the line, you would get 4x the flow.
I had 13# at idle but was only flowing 32 oz. supposed to be 60 oz or something like that.

Mike

 

Thanks guys.....good info. as always...

 

So, for example: a 1/8" fuel line and a stock pump putting out 15psi. Change the line only...say quadruple to 1/2". This should decrease pressure because it has more area to fill. It makes sense to me. That is exactly what I did, and I noticed a drop in pressure by 1#. But I know that I have to be flowing more fuel.

Im gonna go ask one of the pipeline engineers.

 

Thats correct Palmetto.
Where did you get your new lines?
Mike

 

I increased the line size from the FF to the VP to 1/2". Got Rod's bigbanjo fittings ,to go with my Hi-flow Banjo Bolts, from BigBlue. They mate up to a 1/2" Gates fuel hose. I didnt do anything to the rubber line from the LP to the FF though (except Hi-Flow BanjoBolts).

 

OK, this is gonna be a long one.... fetch a cup of your favourite beverage


I don't think it's that simple. First of all there are some points where you can't change the diameter.
The main points are within the VP44. If you measure very close to the VP44 and have a certain pressure there this is equivalent to a certain amount of possible flow into the pump.
If you measure the pressure somewhere back it gets really difficult to correlate pressure to flow since there are a lot of variables. A clogged fuel filter will give you great pressure at standstill (measuring post filter), but whent there is a demand for flow the pressure will drop.
Since there is also a relief valve within the VP44 that will recirculate fuel into the tank when pressure exceeds 15psi (AFAIK) you don't have more fuel available if you up the pressure. You'll have only higher static loads on the seals of the low pressure side. If you take a very big pump ( read fire engine) and use it as a fuel pump you will have lots of flow through the relief valve- since the relief valve is a restriction you will see high pressure.
On lots of European cars the VP44 is used without a lift pump. There it does rely solely on its internal low pressure pump. The only difference is that these engines do use much less fuel per power stroke, but rev higher ( See BMW 530d)- Therefore the relatio between the amount of fuel pumped by the internal pump and the fuel used for injecting is leaving more for cooling and lubrication.
I read a lot about LP failures and I think there are basically 2 types of them. A- doesn't pump but still allows decent flow- won't kill a stock engine VP44. (As long as the fuel filter is OK) -
B- It blocks fuel delivery and this one toasts the inj. pump.
People who do pierce a certain wire will make the VP44 inject a greater proportion of fuel than the internal low pressure pump is designed to deliver ( Assuming everything else is in working order) since you do starve the pump for the needed amount of fuel to cool and lube.
IMHO the way to go for a bombed truck is to deliver fuel (at a decent pressure like 15-17psi) to the VP44 in all situations. If you can pull your fuel pressure down going WOT you don't have enough flow to the pump- either because you have restrictions or because your pump doesn't keep up with the demand. A system showing very high pressures at idle and low pressures WOT is the worst in my opinion.
At the moment I am working on a system that uses several inputs to determine what fuel pressure is needed and to supply it there and then.

Just my ponderings

AlpineRAM

 

Good post, Markus. Good points on all accounts.

There IS a relationship between pressure and flow GIVEN A CONSTANT RESTRICTION. Some of these constants are the parts that Markus mentions-- VP44 internal and such.

Those points where you CAN change the restriction (banjos, etc) WILL change the relationship of pressure to flow, but only at that point! This is similar to a clogged fuel filter. Before the filter, the clog causes HIGHER pressure readings. After the filter, the clog causes LOWER pressure readings.

Since the stock VP can handle 17psi (mine sees that idling warm), I think that's pretty safe.

The "restriction" posed by the VP changes along with fuel demand. So, you WILL see a pressure drop in most cases at high fueling levels. In this case, lower pressure means MORE flow.

I think the case where people report almost no drop in FP at WOT is when they are supplying enough fuel to where the VP bypass is constantly open at lower throttle positions. So when you step on the fuel pedal, there is a surplus of fuel available, and only when the bypass closes to you begin to see a drop in pressure.

My ideal system would also maintain a constant 15-17psi if possible.

Aeromotive makes a cool product that acts like an automatic transmission for your fuel pump. When you need more, it delivers more voltage and the pump then pumps more fuel. At lower demand situations, the pump is "throttled" back electrically. Very cool, imho. I think it uses an electronic (pressure sensing) regulator.

I think this kind of setup is MUCH more efficient than just using a monster pump and regulating it down to where you won't blow out the seals...

Justin