mfi - pump to tank height

Discussion in 'PSI Superchargers Tech Questions' started by noslin, Jul 22, 2019.

  1. noslin

    noslin New Member

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    front engine dragster, MFI, what or where should fuel level be at pump with full tank? should it be right at entry (without fitting) to the pump, can it be 1", 2" lower? what is max differential between the fuel tank level and pump elevation, whats ideal?

    backstory, this is a brand new FED (everything) and our first time dealing with MFI etc. System was flowed and setup by Gene Adams. Just had the Enderle 110 rebuilt by Enderle a few weeks ago. This weekend we went for test run. to make sure everything was ok we fired it at home. filled tank up and no problem starting. the first start with it cold had a little bit trouble but once it ran its fine. started it two more times on the stands at home and worked bitchn. only filled the tank on the initial start.

    At the track a few hours later, put it on the stands and ran it without issue. Made a run and started without issue. came back, looked at data, let it cool a bit, filled the tank to about less then 1" from top (might been 1/2") then went to make another hit but would not start. was using straight gas. the very second he took the bottle away it just died. the last time he tried it he kept it running for few more seconds and died when bottle stopped feeding. We didnt take off the line from pump to BV but from past checking were pretty sure it was dry as bone so its not pumping. further, i looked at the shaft and it is fine on both ends, not rounded, etc.

    So, we got to thinking about fuel tank fuel level to pump elevation. What is minimum height differential between the two. For a dragster i cant see having a 24" tall tank in front. The pump center is about 14.5", pump bottom (not fitting) is about 13". with the pump inlet fitting, the barb is about 10". Ill get solid number on tank but i think the top of the tank is about 12". Fed is still in the trailer but will get it out here shortly and get solid measurements. Ill note pump height while on stands too.


    Thank you
    Dean
     
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  2. nitrowannabe

    nitrowannabe Member

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    Look down at other recent posts. " fuel pump won't suck " has good info for you.
     
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  3. noslin

    noslin New Member

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    Thank you, I have read that thread and have checked everything that has been mentioned in there. the motor has ran and i think a few things contribute to a successful engine start. on the stands the front is a tad higher then the pump, guessing about an inch. also, we think putting oil, or having oil in the pump from blowdown and sitting after race day helped the prime. We feel strongly its an differential issue between fuel level and pump inlet height. but, you guys are the pros and this is new to us so that's why im asking.

    the pump just came back from enderle from a complete rebuild with a new cover. there is solid tubing to the pump. the pump cover is on correctly as we have ran it five times on the stands and made one pass. The hex drive is correct, depth is correct, and it is not rounded on either end or broke.

    here are the numbers at ride height. when tank is full, fuel level is at 11". at ride height the center of pump is 16", bottom of gear is about 15.25. the fuel pump inlet fitting is right at 11.25. which means the tank level is about 4.25" from bottom of pump gear.

    we did some measuring and without making the FED look grotesque with a huge tank up front i can make another tank and get 2" more elevation of fuel in the tank. This would put fuel level at pump about 13" or 2.25" from bottom of pump gear versus the current 4.25".

    looking at the pump with the inlet fitting that has returns, where would be an acceptable minimum fuel level height to have proper suction without issue each time you start? at the bottom of the fuel inlet fitting (about 4" from bottom of gear), or ???

    Also, do people between rounds put little oil down the pump to help with prime?

    Thank you
    Dean
     
    #3
  4. noslin

    noslin New Member

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    was speaking with a knowledgeable friend about the problem and with as full as we are filling the tank the vent is covered and might not be letting the pump suck which would make sense too.
     
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  5. kosky racing

    kosky racing Comp Eliminator

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    I personally run a 6in. pump offset -got it from automan-I use it to lower the pump
     
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  6. HootersFunnyCar

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    Does the pump have an adjustable clamp on housing flange? I have seen the pump body migrate forward in the clamp and disengage the drive shaft more than once.
     
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  7. noslin

    noslin New Member

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    it does have the adjustable clamp. We will check that out for movement.

    another gentleman said if you can turn the pump with your fingers then its worn. even though this was just rebuilt with a new cover, i can spin it easily with my fingers.

    Dean
     
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  8. kosky racing

    kosky racing Comp Eliminator

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    Clamps tight same flange as pump never moves - move pump wherever you want
     
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  9. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    Did you ever check to make sure you have enough end play from the pump drive shaft to the pump drive? If there is no end play it will eat the pump up pretty quick.
     
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  10. noslin

    noslin New Member

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    when we put the pump on originally we checked depths and thought we had the pump end play set correctly. I think this might have to be revisited though as it sounds like it might be too tight.

    Dean
     
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  11. kosky racing

    kosky racing Comp Eliminator

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    If its too tight you ate the pump
     
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  12. noslin

    noslin New Member

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    for GP, is there a preferred method for checking the end play. should i make a plate that is same depth as pump, bolt on and check depth of rod in that fashion or ? When we did it, I just took depth and height numbers of each, calculated the differences etc, adjusted rod for end play. seeing how the end play is small an error would be easy the way i did it.

    Thank you
    Dean
     
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  13. pat Iley

    pat Iley Member

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    i don't believe you have a issue with the height of fuel line causing your problem as we jack the back of our car up and put on jack stands and our fuel tank is up in the nose of the dragster and our fuel outlet in our tank is 8 inchs lower than the fuel pump inlet when we do this and we have been starting it this way for years with no problem. this problem of yours occur after you made a pass and you where able to start it prior to this a couple times. i would suspect that during the run something came lose or was able to move causing this issue. do you have a metal loop line going from the shut off valve to the bottom of the inlet fitting as those have been know to cause issues, i had a pump years ago that acted up and i sent it in complete they told me the loop line had a bad metal flair and they redid it and two runs later it caused me issues again so i replaced with a steel braided line and have never gone back to the loop line. failing that is your issue you might have to do what i did and remove all lines and try re oringing and put lines togetter from the bottom up. just insure the orings and made for methanol or they will not last and you have a no start again. also where is the vent line on your tank that it is under the fuel level when you fill the tank cause this might cause issues with fuel coming out after the burnout and on the starting line causing them to shut you down
     
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  14. OwnBlock

    OwnBlock Member

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    you have caught my attention. i run a blown fed. 1st time ever ive had a tank below the pump. (990 enderle)

    I fitted a cheap 25.00 methanol compatible electric priming pump that tees into the out side of the shutoff. I welded a fitting into the inlet line from tank, put in a very weak poppet. Mounted a switch on the steering wheel, wont run the engine but after our first season on this car, fuel pump hasn't gone away.

    When on the rear jack the car wouldnt run without the bottle. we carry a short board and a block of wood, Lift front up just enough to allow fuel to be primed on the electric pump - engine starts easy and runs perfect. while warming up.

    Yes there is an added line,. I dont run any return lines to the fuel tanks on either of my cars, all run to the base of fuel pumps.
     
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  15. noslin

    noslin New Member

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    We have a steel loop line. before he sent it off, we tested the pump with a drill on the motor and it actually pumped. last night we were bench racing and were wondering if maybe the main bypass was messing up or maybe air between pump and BV creating a lock.

    the way these rigs are setup, its an inherent design issue but these rigs have been running this way since day one. I imagine with the modern design feds the engine does sit a little higher then in the past. one thing we notice is on the stands the front is about 1" higher.

    initially, i had -20 AN hose and fitting from the 1.25 dia. alum tubing to the pump. We thought this was the issue so went to -12 AN hose and lines which seemed to help it start easier. then it just died and this is when my buddy sent the pump in. come to find out it was down 1.5 gpm but it worked... till it didnt (haha). i went ahead and made the feed line solid from tank to pump with just rubber coupler and clamps. put the rebuilt pump on and all good. now, at the track the last pass (only pass) we made, my buddy said he could hear a noise as it started and i rolled out. were guessing it was the pump.

    concerning the loop line, i ordered a new waterman pump last week. Ill make a braided loop line this time for it. Im thinking about getting the cam driven dual drive and rotating it so the pump is lower and then we can move the mag to the front of motor not that its really necessary for what we are doing. but, this would lower the pump almost 1.75" or so.

    concerning the whole system, from top of pump there is the loop line, opposite side is high speed bypass and from pump to BV then off BV there is the idle bypass. the two returns go back to the tank. The tank's vent is 3" tall, at the front of the tank, and facing forward. the vent is baffled or has protection around it so wont fuel wont slosh out.

    I took the tank out, put it on level ground, filled it up while outlet was capped, put the cap on it and then let it free flow. it just pours out full force no problem.

    i took the 110 apart to just look at it and try to understand where the issue might be. ill post up some pics for viewing later.

    Thank you
    Dean
     
    #15

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