Pump loops and main jets

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by Bjs344, Jul 1, 2017.

  1. Bjs344

    Bjs344 Member

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    Please educate me on pump loops so I don't have to go do the math myself.

    I have two cars, one blown, one injected. The injected car has a giant pump loop (.210) while blown car does not. The injected car does not seem to respond to a .010 change in main pills (.120 down to .110), where the blown car that's a huge change.

    Is it just the different combos, or is it the fact that .010 main change with a giant pump loop is too small of a % change to make any difference?

    More generically, does reducing the main from .120 to .110 make less % change if you have a pump loop vs if you have no pump loop?

    I know my blown car is about .001 main per 100' DA, trying to figure out why the injected car doesn't work that way.
     
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  2. Mike Canter

    Mike Canter Top Dragster

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    A pump loop is also called a pump sizer and is used to get rid of excess fuel and get the main jet down into a good range like .075 to .105 size range. Changing a .120 to a .110 is a big change in area of the main jet so a big change in fuel delivery. I would recommend increasing the size of the pump loop to bring the main jet size down into the .076 to .105 range so the percentage of change is less. It appears that your pump on the injected motor is too big so thus the big pump loop jet to bring it down to size. Doesn't hurt to have a big pump loop jet as long as you fuel pressure is in the correct range of 125-130 lbs at 8000 rpm in first gear. The reason your injected motor doesn't react as much to a jet change is that you are pumping way less gallons per minute of fuel into the injected engine compared to the GPM going into the blown motor so changing the main jet has less of a percentage of change to the total GPM of the injected motor compared to the percentage of change on the blown motor
     
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  3. Bjs344

    Bjs344 Member

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    I have the fuel system sized (more or less) for the next motor that isn't done yet.

    I hadn't thought about fuel pressure. According to spuds calculator I have less than 30 psi.

    Obviously that's no good, but what ill effects might you expect. I'm currently seeing huge swings in flash rpm on the converter as well as random down track misfires. Think a smaller nozzle would help?

    At first I thought maybe the pump loop was opening late, but I unhooked the return line and watched it consistently open just off idle.
     
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  4. Mike Canter

    Mike Canter Top Dragster

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    If you have less than 30 psi then you are probably not atomizing the fuel very well and it is probably dribbling liquid down the sides of the intake runners.
     
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  5. Mike Canter

    Mike Canter Top Dragster

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    Didn't hear back from you. Did I answer all your questions ok?
     
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  6. Bjs344

    Bjs344 Member

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    Hey Mike, thanks for all the help, you're always a wealth of knowledge on here.

    I hooked up a gauge and best I can tell I've got a little over 40 psi with .036 nozzles near the top of low gear. I'm going to swap from hilborn to enderle bodies so I can play around with nozzle size a little more (might try a .028 just to take a big swing at it).

    I ran some numbers through the calculator and it seems like I'm fairly close, but I think it's not responding to me leaning it out because the pressure just gets too low. On the initial outing I was trying to get a little response from the plugs and it slowed up a bunch when I finally got a little heat to show on the plug.
     
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    Last edited: Jul 4, 2017
  7. Mike Canter

    Mike Canter Top Dragster

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    Jet flow for main jet and nozzles are normally computed at 150 psi so yes you are correct in that your pressure is so low you don't have much flow
     
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  8. turbo69camaro

    turbo69camaro Member

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    how big of motor what type (bbc hemi etc) what size blades on injector how many GPM is the pump on injected motor
     
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  9. Bjs344

    Bjs344 Member

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    454 BBC street motor. From memory, the blades are 2 7/16 (stacks are tied to an air pan so takes a few minutes to get to the blades).

    Pump is an enderle 110 at about 11 gpm. Motor needs less than 2 gpm best I can tell. Looked back at my notes and pump loop is more like .190 (I just kept drilling out the jet until it didn't flood out when I put it on the brake, then tuned for et and mph from there)

    I have a nice 511 I was hoping to swap out (using same induction as what's on the car now) in a couple weeks, but might be running the baby motor for a while longer.
     
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