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Fuel injection and roots supercharging

Discussion in 'The Hokey Ass Message Board' started by c-10 simplex, Mar 17, 2013.

  1. c-10 simplex
    Joined: Aug 24, 2009
    Posts: 1,371

    c-10 simplex
    Member

    So, just to make clear(for me), If you are running a roots blower AND fuel injection, does the fuel always have to be injected above/before the blower. And if so, why?


    a) on a drag car

    b) on a street driven car. So, here there is a possibility of cruising for many hours continuously.
     
  2. Dave Downs
    Joined: Oct 25, 2005
    Posts: 935

    Dave Downs
    Member
    from S.E. Penna

    I am no expert, but the problem of putting the injector after the supercharger lies with overcoming the pressure boost from the supercharger. Think of it this way - if your fuel injection has a fuel pressure of 10 lbs and the supercharger puts out 15 lbs the fuel is not going to flow.

    A very simple explanation, I'm sure someone can come up with real-world stuff.

    The problem exists wether you blow the boost through the injection unit or put the injector in a pressurized box.
     
  3. R Pope
    Joined: Jan 23, 2006
    Posts: 3,309

    R Pope
    Member

    Dragsters have both above and below injectors. The above injected fuel helps keep the blower cooler, but displaces some of the air being compressed, so much of the fuel goes in below.
     
  4. 57JoeFoMoPar
    Joined: Sep 14, 2004
    Posts: 6,138

    57JoeFoMoPar
    Member

    Are we talking about mechanical or electronic fuel injection?
     

  5. c-10 simplex
    Joined: Aug 24, 2009
    Posts: 1,371

    c-10 simplex
    Member

    Both. Mainly i thought injecting before the blower was to keep the blower cool, but apparently there is more to it than that?
     
  6. joel
    Joined: Oct 10, 2009
    Posts: 2,467

    joel
    ALLIANCE MEMBER

    I believe on new OT cars with electronic fuel management; the fuel goes in "under" the supercharger and the ECU compensates for boost.
     
  7. GMC BUBBA
    Joined: Jun 15, 2006
    Posts: 3,420

    GMC BUBBA
    Member Emeritus

    Correct, the ecu just raises the fuel pressure the amount of boost being developed...you could do the same thing with a vacuum referenced fuel pressure regulator on a plain system...
     
  8. JC Sparks
    Joined: Dec 8, 2008
    Posts: 733

    JC Sparks
    Member
    from Ohio

    The fuel that is injected through the hat (injector) is to seal the strips on the supercharger rotors to create max boost. The fuel that is injected into the intake ports is used for individual cylinder fuel distribution. JC
     
  9. coupemerc
    Joined: Jul 16, 2007
    Posts: 406

    coupemerc
    Member

    For a drag only car running methanol, you want to inject 100% of the fuel above the rotors. This helps the rotor/rotor and rotor/case seal, keeps the blower cool and acts as a mixer to keep the fuel in suspension so it will burn. The problem with injecting 100% of the methanol above the rotors is that you cannot tune your cylinder to cylinder air/fuel ratio. So you must inject a minimal percentage of fuel below the blower to richen up your lean cylinders.
    Years ago when everyone was running just hat nozzels, Ken Veney had a Ford Top Alcohol Dragster that ran okay but was performance limited by one lean cylinder. He ran one additional fuel line down below the blower to the lean cylinder and seven fake fuel lines to the other cylinders and the car became dominant and won everything.
     
  10. It doesn't care where the boost if above or below. Lots of cars ran with a snout driven blower and the boost run to the injector stacks.
     
    Last edited: Mar 17, 2013
  11. FEDER
    Joined: Jan 5, 2003
    Posts: 1,270

    FEDER
    Member

    We run 16 nozzles on our all iron Blown Injected 392. 8 smaller nozzels for the Hat and 8 Big nozzels in the base of the intake. The upper ones are for idle and cool the blower.The lower 8 spray the fuel directly onto the Intake valves. This way You get a cooler fuel charge because the blower heats the fuel. Gene Adams set up Our entire fuel system and We follow it to the tee. He has a little experience at this stuff. Fed
     

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