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This forum has been a lifesaver in the past, and I’m hoping I can get some answers again here. I’ve got a 4BT Cummins swapped into a ‘76 Chevy K10. Engine has bigger injectors, the Super HX30W turbo, and is a VE pump btw. I am planning to install a piston-style lift pump to it ASAP. I ordered one directly from Cummins, seemed to be about as cheap as anywhere else...#3936320...about $120. Anyway my question is this.....is this model pump a low pressure lift pump? Any idea on the max PSI this pump puts out? Apparently I don’t want over (12?)PSI or else I’ll blow the seals out the front of my IP. Lastly, if this happens to be the high pressure pump, can I change the spring out to a weaker spring? Where can I get one? Thanks for any help at all!
 
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The diaphragm pump is considered a "low pressure pump" with min pressure at high idle spec'ed at 3psi. The piston style pump is considered a "high pressure pump" with min pressure at high idle spec'ed at 18psi. I'm not aware of any mods you can make to the lift pump to adjust delivery pressure short of an inline pressure regulator. Is there a reason you went with the piston type lift pump over the diaphragm?

Mike
 

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The diaphragm pump is considered a "low pressure pump" with min pressure at high idle spec'ed at 3psi. The piston style pump is considered a "high pressure pump" with min pressure at high idle spec'ed at 18psi.
There is a low pressure piston pump for the VE IP. The high pressure piston pump is for the P and A series IPs. Nascarmark and Scott(crewcab59) both sell kits to replace the diaphragm pump.
 

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So, does the VE pump require the low pressure piston lift pump and the high pressure piston lift pump goes with the P pump?
Ed
 

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In response to your question, yes, that is the low pressure piston lift pump for the VE injection pump. Part 3936320 may have a newer number 4988751. Don't forget that is only part of the puzzle. You will need spacer part 3914284, 2 gaskets part 3939258, 2 bolts part 3900631, fuel tube part 3927637, and may want to replace the banjo bolt and washer which are parts 3916361 and 3963983. All those extra parts is why most of those kits are several hundred $$$.
 

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Discussion Starter #8
In response to your question, yes, that is the low pressure piston lift pump for the VE injection pump. Part 3936320 may have a newer number 4988751. Don't forget that is only part of the puzzle. You will need spacer part 3914284, 2 gaskets part 3939258, 2 bolts part 3900631, fuel tube part 3927637, and may want to replace the banjo bolt and washer which are parts 3916361 and 3963983. All those extra parts is why most of those kits are several hundred $$$.
Ok, thanks for the input. I was kinda surprised, but I ordered all that direct from Cummins and total was just a bit over $200. So just to reiterate...I can safely run part number 3936320 on my 4BT VE pump, correct? Do you have any idea what the max fuel PSI that pump puts out? Cummins didn’t know.
 

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"Fuel Supply Pump, High Flow Piston Style for VE Pump. Maintains fuel supply pressure of over 7 psi on high output or high performance applications." - Oregon Fuel Injection
 

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Be careful as when I fitted that pump to my 6bt fuel pressure peaked at 15psi which is way too high for a VE IP.
I ended up fitting an adjustable FPR set to keep pressure below 11psi at sea level which should give me a safe limit as we don't have too many mountains over 4,000 ft here in Oz.
Fuel pressure will increase slightly with any gain in altitude.
 

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Those VE piston lift pumps are usually rated in the 12-15 PSI range prior to the fuel filter. You'll lose a few PSI across the filter which gives around 10-12 PSI. at the injection pump. That is safe of a VE so long as the pump seals are in good condition. A pump that didn't leak with a 5 PSI diaphragm pump may develop a leak when exposed to 10-12 PSI.
 

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When I added mine I had to replace the 4.5mm ID o-ring that seals the fuel pin follower in the AFC housing, it had been in the pump for ~ 100,000 miles and was pretty hard so was a weak point to begin with.......
 

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Part # 3936320 is NOT a high flow piston pump. It is 26mm piston pump which makes it standard flow pump. A updated 30mm pump is the high flow pump.
Even at 15psi "at the ve pump" isn't going to blow the front shaft seal out, unless the pump has wear problems ( shaft bearing is worn beyond spec) or seal is an aftermarket seal ( non bosch ).
Many have run as much as 19psi on bone stock older pump without pushing past seal. Granted those pumps are low mileage & in good shape.
My 30mm high volume, low pressure (hvlp) piston lift pumps run at a safe 14psi out of the pump. I like being 1 psi below what bosch considers is a safe psi for the ve pumps, just to be safe & have sold approx 400 of my modified hvlp pumps over the years & to date have not had one customer say they have pushed fuel past the front seal.
 

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Part # 3936320 is NOT a high flow piston pump. It is 26mm piston pump which makes it standard flow pump. A updated 30mm pump is the high flow pump.
Youll have to take that up with OFI. Their idea of high flow and yours may differ. They have a CPL they build to, not extremely high guzzling HP motors. 19psi is foolish with a flimsy lip seal, just asking for a crankcase full of fuel. I know you need to pimp your wares but I spend a lot of money and deal with OFI frequently and have never been disappointed in the slightest with their services. Well known reputation and top notch business. Just saying...theyve been doing fuel injection for 40-45 yrs for a reason.
 

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Youll have to take that up with OFI. Their idea of high flow and yours may differ. They have a CPL they build to, not extremely high guzzling HP motors. 19psi is foolish with a flimsy lip seal, just asking for a crankcase full of fuel. I know you need to pimp your wares but I spend a lot of money and deal with OFI frequently and have never been disappointed in the slightest with their services. Well known reputation and top notch business. Just saying...theyve been doing fuel injection for 40-45 yrs for a reason.
The lip part of the seal is not the problem at all. It's the actual whole seal itself that pushes out with too high of psi. That's why the aftermarket kits are a bad ideal, as they push out even easier. Many loctite the seal in place or stake it and run 30+ psi with the stock bosch ve seal in a high performance application. Not an issue.

Also I don't have a problem with OFI but they can't change physics, so it's not my idea or theirs on what is high volume vs std. The 3936320's 26mm piston is just the old standard size/volume....30mm is physically bigger volume & higher flow rate than 26mm. Also it's the flow/volume that matters the most in a fuel cooled only injection pump like a VE whether it's a stock pump or a high hp one. If the VE gets to warm, it will start bypassing it's pressure & it starts struggling to just maintain case pressure. Many have experienced this and 1st thing they notice is the pump struggles to maintain idle & low rpm running. Once temp raises too far, the case pressure drops & it's just a matter of time before the pump locks up. On a high hp application the higher psi is needed also to maintain case pressure in pump. OFI's statement of maintains 7psi on a high output or high hp application won't cut it, as it would result in 0 psi under WOT.
 

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Ok, well it looks like this pump should be safe to run then! Thanks everyone for their help. I will be picking up my parts from Cummins tomorrow and installing them hopefully tomorrow as well. I will post anything pros or cons that I find after the install.
 

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Also I don't have a problem with OFI but they can't change physics, so it's not my idea or theirs on what is high volume vs std. The 3936320's 26mm piston is just the old standard size/volume....30mm is physically bigger volume & higher flow rate than 26mm.
I dont think they are trying to change physics, Mark. And Im pretty sure they are aware of (as well as everyone on this forum that) 30mm > 26mm. I will explain myself once again as you evidently didnt comprehend the English language I used in previous post. Their idea of high volume may differ from yours as they probably build to a CPL(requiring less fuel than what you build to). The majority of their business is VE pumps(standard) being so many more were produced than P pumps in the 4bt configuration. They rebuild and sell ALOT of 4bt VE pumps, the 393620 pump is a high volume high flow pump compared to the standard equipped diaphragm lift pump.

As stated earlier, maybe you should file a lawsuit or take this up personally with Oregon Fuel Injection instead of teaching the forum members blatantly obvious physics/math.
 

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Your funny as always.
 

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VE pumps should only have a low pressure lift pump.
SO WHEN YOU SAY LOW PRESSURE PUMP ... What pressure are yo wanting.
& Are you telling me I don't need to use the Elec pump from a 2000 24 valve I use this to pump my fuel to the injection pump . I had another tech tell me it was ok if I just used my Elec pump to push fuel to the stock . Push Button manual pump.. But I should not be pushing it to the injection pump.
.. My Way worked for 11 years .. But I'm having issues now .
What do you think.
 

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Up to 16psi max is considered safe for a stock VE pump. So anything less than this psi, is considered a low pressure pump. There is benefits to running the higher safe psi over lower psi. The higher safe psi will allow more timing advance with the higher case pressure. Along with better throttle response and the ability to not go down below unsafe/damage causing 3psi when under high load/rpm. This is specially important if one’s injection pump is turned up & or running bigger injectors than stock.
The reason many say, stay away from an electric pump is almost strictly reliability. The electric pumps also do not have the ability to flow more as rpm goes up, unlike the mechanical pumps do. The 2nd gen Dodge 24v electric fuel pump was 13psi on its best day but that style of Carter pump was known to live a short life. The stamped housings weren’t perfectly round & the vane style components would slowly cause wear, much faster than any mechanical lift pump.
The piston style pumps are the champs of longevity and even when they start failing, they can’t pump fuel into the crank case, unlike the mechanical diaphragm pumps.
 
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