Pd high pressure inline pump?

Mahliloltdi

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I have put a few pd lift pumps in alh's with good results and couldn't help but not see if anyone ever put an inline high pressure pump with a pd motor. The stock lift pump puts out around 8psi, what if you bump that to 25+ going into the tandem pump? I figured it would be good for high HP builds where more fueling is needed.. may be wrong about that idk!.. if anyone's done it, does it run better and what kind of power difference was there. let me know what you guys think
 

[486]

Top Post Dawg
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Seems the tandem pump puts out something like 100 PSI, so you could probably just run an 044 bosch pump inline and ditch the tandem pump all together.
 

Mahliloltdi

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Okay, but i'm saying do you think more psi going into the tandem pump, would mean more psi out of the tandem pump, for more fueling?
 

oilhammer

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Are you running out of fueling? The PDs have a lot of extra fueling available already, I am not sure what you are talking about is going to do anything. Sounds like a solution in search of a problem.

The main injection pressure happens inside each injector. The lift pump and tandem pump only need to provide enough volume inside the tube in the head to load each injector. There is WAY more fuel going through there than the engine could possibly burn I would think, since most of it even under high load demands is still being returned to the tank.

The VE cars can benefit from an electric assist pump because under certain situations with higher output engines the fuel demand in the pump can cause cavitation because the little mechanical suction pump has a difficult time keeping up, as it is tasked with pulling fuel all the way from the back of the car up and through the fuel filter.
 
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Machineman

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We were going to do what 486 said ditch the tandem pump and run a high pressure gas pump into it we ended up just running high pressure into the tandem pump with mediocre results I don't think the tandem pumps after much pressure is more less volume
 

Mike_04GolfTDI

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The tandem pump is a rotary-vane style pump inside. This means it has positive displacement.

It only requires enough pressure going in so that it will fill with fuel. More pressure than needed will not result in more output because you can't really compress the fuel. If it was air, then yes, more pressure will get more air in, but not with fuel.

When my in-tank lift pump was dead, I didn't notice any reduction in power, even with a tuned car. If the lift pump works at all, you're good. The tandem pump is supposed to have a little bit of positive inlet pressure, so it isn't sucking fuel in, but rather having it pushed in. This is probably to prevent cavitation, which I could see damaging the tandem pump.

https://en.wikipedia.org/wiki/Rotary_vane_pump
 

Machineman

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The tandem pump is a rotary-vane style pump inside. This means it has positive displacement.

It only requires enough pressure going in so that it will fill with fuel. More pressure than needed will not result in more output because you can't really compress the fuel. If it was air, then yes, more pressure will get more air in, but not with fuel.

When my in-tank lift pump was dead, I didn't notice any reduction in power, even with a tuned car. If the lift pump works at all, you're good. The tandem pump is supposed to have a little bit of positive inlet pressure, so it isn't sucking fuel in, but rather having it pushed in. This is probably to prevent cavitation, which I could see damaging the tandem pump.

Well said!
 

pdq import repair

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If you could get more fueling without any other mods it would not produce more power, likely more smoke if anything.

More smoke does not equate to more power either unless you ask the lifted truck crowd.
 

Machineman

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If you could get more fueling without any other mods it would not produce more power, likely more smoke if anything.

More smoke does not equate to more power either unless you ask the lifted truck crowd.

Exactly I've actually noticed over fueling a diesel creates less power I think it's something to do with putting out the fire got to keep the Lambda values reasonable
 

[486]

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Exactly I've actually noticed over fueling a diesel creates less power I think it's something to do with putting out the fire got to keep the Lambda values reasonable
that's only when the exhaust looks like RTV coming out

you do gain power from when it just starts smoking to some point a little bit beyond stoich

As a fun aside, BSFC is actually at its lowest when there's just the slightest haze, as you aren't pumping unused air. Stationary diesels long ago used to have rudimentary variable valve timing to achieve this with varying loads.
 

Machineman

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that's only when the exhaust looks like RTV coming out
you do gain power from when it just starts smoking to some point a little bit beyond stoich
As a fun aside, BSFC is actually at its lowest when there's just the slightest haze, as you aren't pumping unused air. Stationary diesels long ago used to have rudimentary variable valve timing to achieve this with varying loads.
Yes that's what I'm talking about haha running 160s with 35 degrees duration with a 300 CFM Turbo when you put it to the floor the boost gauge goes down lol and yes I agree I usually like to see my diesels with a slight Haze Under full load
 

pdq import repair

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Slight haze is fine, the brain dead's around here go far beyond that.

I have a couple of cop friends and they say if they can catch them on a dashcam they are more than happy to cite them. With no camera footage they can appeal to the judge and maybe walk on the charges.

I am all for modifications for power, and done properly they don't fog much.
 

Mahliloltdi

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Agreed, let all the cool truckers smoke out Priuses while I pass their a$$es in my almost smoke free, compound turbo TDI:cool:. Appreciate everyone's feedback about the pump, wasn't necessarily planning on doing it.. mainly wanted to see if it's been done!
 
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