Engine/Transmission (1998.5 - 2002) If the Vp44 is calibrated at 13.5 psi, what's the calibration rpm?

[rweis]

On the RASP brass bypass regulation of the VP44 input pressure -



The approach I am going to try is have one brass regulator that starts bypassing fuel at 12 psi to the tank, but have a second brass regulator that starts bypassing fuel at 15 psi, sort of a two stage thing to limit the VP44 input range to 12 - 15 psi.



I think it might be really hard and wind up too much of a compromise to get one brass bypass to work in a narrow range with the truck not carrying a load, then also function correctly in the same range when the truck is carrying a load with very different throttle / fuel requirements.



One brass regulator to start bypassing and cover the low end psi, then a second brass regulator with slightly different characteristics to kick in to help pass the higher volumes of fuel at full throttle and not go significantly higher in psi.



Finding just the right spring for one regulator to do everything might be really difficult if not impossible. Playing 2 regulators off against each other may be a little more tedious to get it set right, but may be more flexable in the long range of psi that can be easily managed. Anyway that is the direction I am going to try first.



Bob Weis

 

[rweis]

The 2nd bypass arrived set for 15 psi with a . 028 spring, 1 thick shim, 5 thin shims.



1 thick shim is equal to 6 thin shims or thick = . 186" ,thin = . 030", or . 336" of shims.



I also got springs of . 016, . 018, . 019, . 021, . 024, . 028, . 032, . 036, . 039, . 042.



Now I have to figuer out the spring rates and how it works in our system.



The concept is to have one one bypass set to NOT open until the minimum psi of 13 psi then start to open so the minimum psi the VP44 will see is 13 psi. Then have the second bypass valve start to open at 14 psi.



EDIT #1



Rethinking this it may be easier to have both brass bypasses set to 13. 5 psi (or as close to that as possible). That way both would have the same number of shims with the same spring. Just easier to setup. I think a machine shop will have a dial gauge that can tell me what the psi loading on the internal bypass piston is, and if so that is how I will set the shims.

edit



As RASP pressure goes above 13 psi the 1st valve starts to open and IF the fuel flow increases to 14 psi then the first bypass valve will be partially open and opening more and more, but the second bypass valve will start to open at 14 psi and relieve the first bypass valve from passing all the fuel.



Therefore putting less total pressure on the first bypass valve and letting it maintain an equal amount of face pressure to the second bypass valve.



Both bypass valves are 3/8" ID so the should be able to divide up the total flow from a AN-6 line easily.



On the reverse, as RASP pressure falls below 14psi the second bypass valve should be closed and then the first bypass valve continue closing until 13 psi when it is fully closed. I actually do not think that the first bypass valve will ever fully close unless the VP44 is taking the total output of the RASP.



Ideas?, comments?



EDIT #2



3 extra RASP springs will arrive tommorrow by UPS. I have "modified" my VP44 brass bypass to operate at a little lower value than as I remember it was initially set. The Kinsler and the RASP bypass valve springs are different physical lengths.



I am going to put the Kinsler valve where the RASP lp valve is, then form a parallel pair of RASP bypass valves to see if in parallel it will cut the individual valve travel by one half and therefore the pressure differences by one half and then fine tune the pair of valves to as close to 13. 5 as possible with shims. With the RASP springs a little physically longer than the Kinsler springs the rate of travel of the RASP springs should be somewhat less and the overall pressure differentials should be somewhat less as well.



EDIT #3



Well so far the setup is 1 DTT brass VP44 bypass and a Kinsler in parallel.



The RASP spring is a . 038. I had cut on it to give 12 - 16 psi.

Interestingly enough, the cut length of the DTT spring was exactely the length of the Kinsler un cut spring.

I put in a Kinsler . 038 with no shims.

Results: 9psi - 15 psi

Note: at idle at 9spi I had some failed injection events (engine ran "rough" and missed some injection events).



Next I changed the Kinsler to a . 028 (to be a little softer to lower the upper psi) with a . 183 shim to raise the lower psi.

Results: 12 1/2 psi at idle - 15 1/2 psi

Note: at idle at 12 1/2 psi there are no missed injection events



I feel the DTT parallel valve needs to be swapped to a Kinsler with a . 028 and the . 183 shim (ie identical). I think the upper psi will come down a tad as the max on the DTT valve was 16 and I think the softer spring of the Kinsler is doing like 3/4 of the bypassing and I need to even that up some. I can also swap spring easier and know what spring is doing what with identical parallel units and know the springs are exactely matched to the valve (the DTT internal bore is . 05 larger than the Kinsler and I am concerned that the slightly cocked off center spring might cause the valve to not operate exactely smoothly if I use a Kinsler spring in the DTT valve).



EDIT #4



Well, I spent the entire day adjusting the springs and shims on the VP44 Kinsler brass bypass I have to regulate the pressure the VP44 sees. I ran about 15 different spring / shim sets with the Kinsler brass bypass in both positions.



Sometimes frustrating, sometimes confusing, always a challange.



In the end I got to 11 psi idle (850), 12 psi 1000 rpm (1. 5 psi low) then a slow psi rise to 14 psi at 2200 rpm (. 5 psi high), and finally 14. 5 at 2600 rpm (1 psi high). Most of my driving pattern is in the 1200 - 2000 rpm range and will generally be in the +- 1 psi range.



That is as close as I could get it. Brady at II had a reply to VP44 psi and said the target was 13. 5 as the rpm increased to minimize internal pump stress. I took the approach that if I was going to be off much it was going to be at lower rpm's and more accurate at higher rpm's.



I will run this configuration and report back it I see anything that needs changing. I know OAT > ~ 90 will cause a 1 psi loss, but I will have to see what happens with the spring / shim configuration I have and see if that still holds true.



The spring / shim combination turned out to be . 021 springs with 2 @ . 186 shims + 3 @ . 030 shims (almost 1/2" of shims). Seems the shims set the lower psi and the spring rate set the high psi. It took . 462 of shims to get the spring low end curve close to the actual spring rate.



I checked that the spring was not going solid and there is spacing between the coils even at the high end.



Bob Weis

 

[rweis]

TTT final settings (I think)



Bob Weis

 

[Gary - K7GLD]

Got my own homebrew regulator installed right at the VP-44, where I also take my fuel PSI readings:



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After 3 tries on spring length, hit PSI dead-on at 15 PSI - steady as a rock, until heavy load draws it below the set point - I'm figuring to try replacing my 7 PSI Carter pusher with my spare OEM LP - the extra 10 PSI or so I would gain MIGHT fill in the PSI "hole" of heavy demand under load, and completely stabilize PSI under ALL circumstances - plus, the swap of pumps can be done in just a few minutes because they are externally identical...