How to modify the overflow valve OFV

Big Blue24

Big Blue24

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Step 1: Remove the overflow valve.

OFV002.jpg

OFV003.jpg

OFV004.jpg


Step 2: Use 3/4" wrench to hold the valve and remove the smaller 12mm nut to disassemble.
OFV006.jpg

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Factory shims used to adjust pressure when valve is initially built.
OFV010.jpg

Step 3: Take ordinary pen and remove the internal spring. Notice that the winding of a pen spring is opposite of the winding of the stock OFV spring, this will prevent the two springs from becoming tangled up inside the OFV.
OFV012.jpg

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Step 4: Stretch the OFV spring just a little bit, try to make it about 1/8" longer. Then install the pen spring inside the slightly stretched OFV spring. Then trim the pen spring so when it's installed, it's even with the slightly stretched OFV spring. If the pen spring is left too long where it sticks out past the OFV spring pressure will be high 55 psi or so, if the spring is trimmed even with the slightly stretched OFV spring, pressure will be perfect at about 40-45 psi, if pen spring is cut a little short, pressure will be around 30-35 psi which is still a lot better than stock but a little low for a high performance setup.
OFV015.jpg

Step 5: Reassemble the valve and reinstall it on the injection pump.

OFV016.jpg
 
but you still didnt increase fuel supply. If you have to trick a pressure gauge then yoou need a bigger pump. just saying.

i run my ad150 40 psi on a unmodded valve and it holds 35psi down the track. i guess i dont understand.
 
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Just put a solid bolt in that b**ch. All fuel will have no choice but to go out of the injector....LOL
 
SCHOOL BUS said:
im stupid. what does that do?
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With a modded valve, the valve will close when pressure falls 5-6 psi. If you setup the OFV to make 45 psi at idle, the valve will close right about 40 psi, then every drop of fuel your lift pump makes will end up in the injectors instead of running through the OFV and down the return line to the tank.

A stock worn valve holds about 22 psi at idle and doesn't fully close till about 16-18 psi or in some cases when the spring is broken, it never fully closes. The injection pump cannot provide maximum fuel delivery when there is just 16-22 psi fuel pressure.

In short, modifying the OFV decreases the amount of fuel bypassed/bled-off down the return line thereby retaining more fuel volume and pressure in the injection pump.

If your current lift pump setup does not supply the injection pump with an adequate supply of fuel, this modification will increase the amount of fuel and pressure available to fill the injection pump barrels which directly results in more fueling and generally more horsepower.

The amount of fueling and power gained will be most directly related to how much fuel starvation is occurring in your particular setup. My 95' Junker Drag Truck picked up 83 HP at the rear wheels from providing adequate fuel pressure to the injection pump.
 
ILLINOISRAM said:
but you still didnt increase fuel supply. If you have to trick a pressure gauge then yoou need a bigger pump. just saying.

i run my ad150 40 psi on a unmodded valve and it holds 35psi down the track. i guess i dont understand.
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If I had to guess, in your situation, your 150 gallon per hour pump is providing enough fuel to feed the injection pump and has enough extra capacity that it's maintaining 35 psi even though it is bypassing fuel at the overflow valve.

Assuming you run an OFV, if you modified it, the valve would close completely at 40 psi and you'd be able to maintain 39-40 psi running down the track. Who knows your 13mm pump might provide a little more high rpm fuel if it's fed with 39 psi instead of 35 psi.

And just to be clear, modifying the OFV does not increase lift pump output, obviously, it simply prevents bypassed or wasted fuel from running into the return line and instead causes all lift pump supplied fuel to dead-head at the injection pump.
 
if i run 35 psi now, thats telling me i have plenty of not needed fuel. My brother made 591hp on a stock lift pump, unmodded overflow valve. We never had a fuel pressure gauge but im sure there was not very much pressure at that point. Then we upgraded to the ad150 and havn't dynoed, but didnt notice any more smoke, no change in boost or egt. If it did make a differance, it was very minimal atleast by the seat of the pants. Which we know how accurate that can be.LOL
 
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I think it's more intended for trucks with untouched worn out springs. Stretch it out to get it back to normal. When people say it added oh so much power, it's probably just low spring tension, and it's the power it should've had anyways
 
probably a newbie question but is it possible for a worn out spring to cause a truck not to start? allowing too much fuel to pass through the pump and not get enough to the injectors.
 
CGD said:
probably a newbie question but is it possible for a worn out spring to cause a truck not to start? allowing too much fuel to pass through the pump and not get enough to the injectors.
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Doubtful, there should be enough restriction from the length of the return line alone to force the pump to use at least some of the supplied fuel. It would start, but run poorly as the rpms increase.
 
Just kink the return line :p :p :p joke!

Thanks for the write up, Im going to install a fuel pressure gauge and I will have some before/after info. One question this was done with the stock lift pump correct?
 
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