Hypothetical fuel pressure question

Discussion in 'InsideTopAlcohol.com Tech Questions' started by Big Steve, Sep 15, 2019.

  1. Big Steve

    Big Steve Member

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    I know most seem to like pressure in the 130 psi range but know of some running as high as 190-200 psi.

    Let's say Same blown BBC, same 30 PSI boost, same pump, same 85 bypass pill, no hi speeds, what performance differences would you see with a nozzle area giving you 135 psi versus a nozzle area giving you 190 psi?
    What is so magical about that 130 PSI range that most seem to recommend?
     
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  2. Mike Canter

    Mike Canter Top Dragster
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    I have tried real high pressure and what I call normal pressure or 125-130 lbs at 8000 rpm at the pump. Didn’t make and difference to performance. Being too low definitely made response at lower rpm right after launch bad.
     
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  3. Dave Koehler

    Dave Koehler Member

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    I realize what you are trying to ask but your example is wrong.
    Assuming a good tuneup to begin with.
    With no main change the smaller nozzles will increase pressure but the gpm going in will be less. Lean time.

    To get the higher pressure and the same GPM going in you will need to reduce the main jet along with the smaller nozzles.
     
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  4. Big Steve

    Big Steve Member

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    Dave. Yes I understand that, Question was very hypothetical but what I am after is there a performance difference between nozzle atomization at 130 psi verse 190 psi on a good tune up
     
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  5. Dave Koehler

    Dave Koehler Member

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    All I ask for is hypothetical correctness. :)

    As to a HP answer you will need to talk to someone that has had your combo on a dyno and tried it....and is willing to discuss it.

    Other than that you will run into countless examples of "I know somebody who.....".

    Somewhere I have some photos I took of the fuel spray out of a nitrous plate. Looked like a seriously cool fog until I took a flash photo of it.
    Let's just say that atomization might just be a relative term.

    Best thing to do is during a period of time where your deal is consistent make the change and see where it leads. You knew that already I suspect.

    FWIW, There may be something there depending on your chamber design but do not expect life altering results.
     
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  6. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    I have seen some alcohol fuel systems with a fuel pressure close to 400 lbs. Those cars weren't any faster than the 'conventional' fuel systems.

    Higher pressure systems are definitely harder on the pump.

    Each jet size change will result in a bigger change in flow.

    I have tuned, run and consulted on a wide variety of cars and did not see anything that made me think a high pressure system was better.

    Anything that is 'atomized' will form back into droplets if it hits a solid surface. Even when the valve opens, there's a lot of obstacles between your nozzle and the chamber. I think most of the vaporization happens on the compression stroke.
     
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  7. Big Steve

    Big Steve Member

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    Yea what I should of said in the original post, Hypothetically same BBC engine at 30lbs boost with a pump flowing the same 10GPM at 8K RPM what would the performance difference be to having a nozzle area that produces 130 psi and and one at 190 psi.

    I am guessing none to very little but trying to open up some discussion on opinion
     
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  8. Big Steve

    Big Steve Member

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    So Will, what is your fuel pressure "happy range" that you like to tune in?
     
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  9. Mike Canter

    Mike Canter Top Dragster
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    I think if the pressure is too high then the port nozzle spray will hit the opposite wall of the runner and change into unatomized fuel and run down the side. The understanding I have is that the Enderle nozzles are designed with 150 lbs being a mid Point for correct atomization
     
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  10. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    As a general rule 150.

    I don't like to see my main jet get over 110, preferrably 100. Usually use the pump loop to get the main in range between 70-110. Sometimes on bigger swings in DA will change nozzle area as well.
     
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