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  #1  
Old 11-27-2013, 12:37 AM
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Increasing lift pump pressure

I've been thinking on how to get a cheap power increase, and have to wonder what would happen with increased fuel pressure. I know as the outlet fitting spring gets weak, the pressure drops, and performance is lost, but what about installing some sort of regulator on the return line? I'm not sure what the lift pump is actually capable of putting out, but say it's at 3psi now and I regulate it at 8psi, would it be reasonable to assume it'll gain a bit of power?
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Old 11-27-2013, 12:47 AM
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Quote:
Originally Posted by 4x4_Welder View Post
I've been thinking on how to get a cheap power increase, and have to wonder what would happen with increased fuel pressure. I know as the outlet fitting spring gets weak, the pressure drops, and performance is lost, but what about installing some sort of regulator on the return line? I'm not sure what the lift pump is actually capable of putting out, but say it's at 3psi now and I regulate it at 8psi, would it be reasonable to assume it'll gain a bit of power?
Hi,

which engine?
There is already a spring loaded valve directly on the IP outlet.
Usually this opens at about 1 - 1.5 bar. Old style valves can be disassembled and the spring can be stretched to make approx. 2 bar.
The lift pump spring can be shimmed. Assuming all is clean and the non-return valves of the lift pump are new you should see about 2-2.5 bar on the inlet of the IP.
A small step but it helps.

Tom
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Old 11-27-2013, 02:16 AM
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This is on an OM617. That is a bit higher of pressure then I thought they ran, does it make a noticeable difference in performance or is it just smoother?
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  #4  
Old 11-27-2013, 12:32 PM
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if the lift pump is almost new I'd leave it as it is.
In case you need to take it out anyway, it is just the 2 springs additionally to put your hands on.
Whether you could see an improvement can tell you a fuel pressure gauge.
Of course from an almost dead lift pump to a pimped one is a huge difference.

Tom
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  #5  
Old 11-27-2013, 07:24 PM
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Quote:
Originally Posted by 4x4_Welder View Post
I've been thinking on how to get a cheap power increase, and have to wonder what would happen with increased fuel pressure. I know as the outlet fitting spring gets weak, the pressure drops, and performance is lost, but what about installing some sort of regulator on the return line? I'm not sure what the lift pump is actually capable of putting out, but say it's at 3psi now and I regulate it at 8psi, would it be reasonable to assume it'll gain a bit of power?
Off the top of My head the pressure range for a good Fuel Pressure Relief/Overflow Valve is 8 psi at idle and 18 psi on the top end on a 617.952.
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  #6  
Old 11-28-2013, 12:58 AM
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It shouldnt matter much!

Hi All!
The only purpose of the lift pump is to supply fuel to the pumping elements at a high enough pressure to ensure the element cylinders are completly full before the plunger moves up to close off the inlet port. Anything above that pressure makes no difference since fuel is basically incompressible, so you cant squeeze any additional fuel into an already full cylinder. The volume of the cylinder is what determins how much fuel will be injected and therefore the amount of power produced.
Now maybe at insanely high rpm you could possibly run into a situation where there wasn't enough time for the cylinder to fill completley. This would cause a loss of power due to the cylinder not being full. Then additional lift pump pressure would help because the fuel would fill the cylinder faster due to the increased pressure.
I don't know if our engines can turn fast enough for this to be a problem or not! I hope this helps!
Cheers!
Chris
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  #7  
Old 11-28-2013, 01:40 AM
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Mmmmm interesting - what is the maximum rpm limit on a mechanical IP...
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Old 11-28-2013, 10:07 AM
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Quote:
Originally Posted by 4x4_Welder View Post
I'm not sure what the lift pump is actually capable of putting out, but say it's at 3psi now and I regulate it at 8psi, would it be reasonable to assume it'll gain a bit of power?
you can pinch the return line after OFV to examine if stretching is needed
if you have weak LP you have to replace it...
IMHO pimping the lift pressure above factory will not give you any HP
hose and clamps leaks more likely

cheers
ChO

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Old 11-28-2013, 11:16 AM
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Originally Posted by Stretch View Post
Mmmmm interesting - what is the maximum rpm limit on a mechanical IP...
Rumor is 7k (don't remember the model probably a crazy 606 build) but I don't have proof offhand
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  #10  
Old 11-28-2013, 12:00 PM
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I got a power increase climbing mountains with a electric fuel pump pushing about 9 psi.I miss having a electric pump
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  #11  
Old 11-28-2013, 12:54 PM
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Answer

Quote:
Originally Posted by 4x4_Welder View Post
I've been thinking on how to get a cheap power increase, and have to wonder what would happen with increased fuel pressure. I know as the outlet fitting spring gets weak, the pressure drops, and performance is lost, but what about installing some sort of regulator on the return line? I'm not sure what the lift pump is actually capable of putting out, but say it's at 3psi now and I regulate it at 8psi, would it be reasonable to assume it'll gain a bit of power?
My 240D arrived with a weak - collapsed bypass spring "13 MM" which tested at 2 PSI = engine had Good idle, poor mid - high RPM response/power.

After stretching to 31 MM, pressure tested 28 PSI = engine had Good idle, great mid, and good high RPM response/power..

As a note: When in doubt, I pinch off the return line, and take the vehicle for a quick drive = usually 0.5 - 1.5 miles will show if there will be improvement...

.
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  #12  
Old 11-28-2013, 02:10 PM
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Thats a cool trick whunter! I'll remember that!
cheers
chris
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  #13  
Old 11-28-2013, 06:37 PM
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I know that the old 6BT Cummins engines have greatly varied performance depending on input pressure to the IP. I guess I'll just have to experiment with it to see what the difference is. I'll try to do it on a dyno day to get some real info.
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  #14  
Old 11-29-2013, 03:22 AM
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Originally Posted by Simpler=Better View Post
Rumor is 7k (don't remember the model probably a crazy 606 build) but I don't have proof offhand
So only 2K extra then...

...not really worth it eh? I'd want at least 14K at the IP!!! (28K at the crank - yeeeee haaaar)
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  #15  
Old 11-30-2013, 06:38 PM
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Originally Posted by Bio240D View Post
Hi All!
The only purpose of the lift pump is to supply fuel to the pumping elements at a high enough pressure to ensure the element cylinders are completly full before the plunger moves up to close off the inlet port. Anything above that pressure makes no difference since fuel is basically incompressible, so you cant squeeze any additional fuel into an already full cylinder. The volume of the cylinder is what determins how much fuel will be injected and therefore the amount of power produced.
Now maybe at insanely high rpm you could possibly run into a situation where there wasn't enough time for the cylinder to fill completley. This would cause a loss of power due to the cylinder not being full. Then additional lift pump pressure would help because the fuel would fill the cylinder faster due to the increased pressure.
I don't know if our engines can turn fast enough for this to be a problem or not! I hope this helps!
Cheers!
Chris
That is also what happens when the Fuel Pressure is to low. The Element does not have enough time to fill.

There is also a lot of turbulance and pulsation going on inside of the Fuel Injection Pump Housing because each Element also expells Fuel out of the Feed Port. So there needs to be enough pressure and flow so that that turbulance does not interfere with the filling of the Element.

There is also supposed to be enough volume going through the Fuel Injection Pump to cool it.
Although there are Inline Fuel Injection Pumps on other Engines that do not have retun Fuel from the Fuel Injection Pump Housing. However, they use Diaphragm Fuel Supply/Lift Pumps and you need to open a Screw to Manually Bleed the Air out of Them.
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