Blower surge cure?

Discussion in 'Pit Buzz' started by Compresser, Aug 1, 2021.

  1. Compresser

    Compresser Member

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    Having the blower surge curse.
    At idle with surge I can see butterflys mving in and out as the idle goes up and down.
    I can put my finger up against the butterflys and slow the surge a bit. I can still feel the butterflys moving with my fingers on them.
    So my thought and qustion is this.
    Has anyone tried shutting the butterflys compleatly and using some sort of needle valve in the hat to regulate the idle air and if so where did you get the needle valve?
     
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  2. jeffj

    jeffj Member

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    If your BV adjustment is very rich it will cause the surge.
    Leak down the BV to see what it is at so that you can return to the same setting if you need to. Then lean the leak down number a bit and fire the engine and see how it is; if it still surges lean it more till the surge goes away but not so lean that it stumbles when you crack the throttle. You can lean it till it stumbles and then richen it just till the stumble goes away. Then with the engine off leak the BV again to see what it is at. This will allow you to see the spread between too fat and almost too lean. Then decide where you want to set it between these 2 parameters based on how hot or cold you want the engine to idle.
    Jeff J
     
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  3. kosky racing

    kosky racing Comp Eliminator

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  4. kosky racing

    kosky racing Comp Eliminator

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    If your idle check is to low this can happen If the bv is to rich it causes the check valve to go up and down every system needs its own percentage and pressure for each type of blower and engine needs
     
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  5. Compresser

    Compresser Member

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    Jeff an Mr. Kosky, thank you for your reply.
    I have had th BV any way from 60% to 100% I should have stated that I can get a smooth idle untl i put it in gear.
    I had not thought about the idle bypass. I will check it out.
     
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    Last edited: Aug 2, 2021
  6. Compresser

    Compresser Member

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    I just pulled up my data recorder file and at idle the pressure is only 1 PSI and steady. What PSI should I have the idle check set at?
    I am reading the fuel pressure at the hat distribution block.
     
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  7. jeffj

    jeffj Member

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    Exactly what Mike said!
    When talking about "fuel pressure", the standard reference would be the pressure at the pump discharge. Everything down stream from that will affect the flow volume and the pressure; eg the idle check pressure, any pump sizer jet and check pressure, the cut in the spool in the BV, the port check pressure, plus any lean out jets and check pressures. Pressure at the hat block is down the food chain from some of these so it is not really easy to comment on it.
    You need to measure pressure at the pump. You need to be sure your checks are SEALED, not weeping. You need to take them off, apply air to them in the direction of flow and see the pressure at the point it "Cracks" and flows air, not weeping but it pops and flows air.
    Fix any weeping....did I mention to fix any weeping? because it will mess up your settings. You know how to get a valve to seal with the seat in a cylinder head.....
    I do not know what equipment you have; you just mentioned getting it smooth until it is put in gear so I assume you have a converter car, way different than a clutch car; roots blower, way different than a screw blower because of the heat and boost levels and curve.
    What is your idle check pressure set at right now? I tuned a nationally competitive alcohol dragster up to the end of 2013 and have my logs of every setting for every run but I don't think that is what you are running right now. Air check your poppets and tell me what they are at and I will try to point you in the right direction.
    Jeff Johnsen
     
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  8. kosky racing

    kosky racing Comp Eliminator

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    Start at 6#s and as far as 20#
     
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  9. Compresser

    Compresser Member

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    OK Jeff and Mr. Kosky.
    You want me to check fuel pressure before the BV is this correct?
    Yes this is a PG with TB brake. Chevy 540 CI. 11:1 CR 1471 hi helix roots. No high speed 13GPH pump. SQ BV. On alcohol.
     
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  10. jeffj

    jeffj Member

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    Yes; pump pressure before the BV.
    The square BV is a bit limited for flow but your 13 gph pump should be OK. If you want to add a high speed you should plumb it in with a check valve before the BV so that the fuel flow for it does not have to go through the BV. Air check the crack point of the idle check as you currently have it.
    Jeff J
     
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  11. kosky racing

    kosky racing Comp Eliminator

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    check your return valve with a good regulator by itself not on the block
     
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  12. Compresser

    Compresser Member

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    Mike and Jeff. Just checked idle return poppet.
    It opens at 3PSI.
    This is with the poppet hooked directly to my CO2 bottle with a 0-15 psi gauge regulated.
    I have a shim and spring kit somewhere in the trailer. I will set it to 6-10 when I find the shims.
    Thanks for the advise.
    I should have engine back together by the end of the month and will proceed with idle check.
     
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  13. jeffj

    jeffj Member

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    I would go up to at least 10 psi and as Mike said you can go much higher than that; it would not be too much to go as high as 15 psi or more but you want to start looking at cyl head temp. When you do the idle psi increase you will need to do the BV leak procedure again, as I described earlier. Good luck. Jeff Johnsen
     
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  14. Compresser

    Compresser Member

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    Jeff. I have tried lapping this idle check valve as it does weep. I have not been successful in getting it to not weep. The seat appears to be just a square lip, no matching taper to seat against the poppet. What other method do you suggest to make this valve seat?
     
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  15. jeffj

    jeffj Member

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    The Enderle checks are brass with a steel "needle" and spring although there are others out there. Assuming you have brass Enderle poppets, you just work that seat until it seals. Look for any damage to both the needle and the seat causing the weeping. I hesitate to say this but the idle check is the one check that weeping matters somewhat less. If it is not flat out leaking, when the engine starts it has to immediately blow open to control idle pressure anyway but with the engine off it will allow the fuel system to drain back, not retaining fuel in the system above it. It could then make it harder to start the engine or initially to keep it running until all air was purged from the system. You should perhaps buy a couple of new complete Enderle check valves; they are not too expensive and you eliminate tons of gremlins if your system does what it is supposed to do with no leaks. Time spent lapping to get a good seal is only time. Getting a good linear and repeatable fuel system assembled is time well spent. Jeff J
     
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  16. MKR-588

    MKR-588 Member

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    Just wondering how things ended up? have you had a chance to fire it up yet?
     
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  17. Compresser

    Compresser Member

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    A follow up on the above.
    I ended up buying a new idle check valve and set it at 17 PSI.
    Finally got back out to the track. I reset BV leak down to 78% and with a bit of butterfly and BV adjustment was able to get a fairly smooth idle at 1300 RPM in gear.
    Had transmission issues so did not get to make any runs. The higher PSI idle check certainly richened up the idle based on the eye burning index and fuel consumption on warm up.
    Thank you to all for the advise and suggestions.
    Now that the summer heat here in AZ is starting to let up there will be more time made to go race.
     
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