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ferrari/webber fuel pump theory

Discussion in 'Technical Q&A' started by pcelenta, Mar 4, 2004.

  1. pcelenta

    pcelenta Karting

    Nov 1, 2003
    216
    been having problems since replacing my original corona pump with a holley red pump and regulator set to 4 psi...car starves for fuel under hard throttle and in turns. specs on the factory pump are 100 litres per hour (around 25 gph) and 3 + or - 0.5 m. h20...what is m h20? is it the same as PSI?

    the holley specs are as follows: 97 gph @7psi...71 gph @4psi...so it would seem to be a sufficient replacement. someone on the chat replaced their corona with a facet blue top that puts out 6-7.25 psi @35 gph and no regulator with out problems.

    the issues I am trying to figure out are...what is most important? GPH or PSI? If I have a fuel return line is PSI as big of an issue and will that help prevent flooding? I am considering removing the regulator and if that doesn't work switching pumps...any thoughts?

    Regards,
    Paul
    78 308 gts
     
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  3. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    19,345
    Texas
    Full Name:
    Steve Magnusson
    m. H20 is "meters of water" (i.e., 1 m. H20 is the pressure required to support a column of water 1 meter high).

    It converts to 4.267 +/- .711 psi so you're in the right ballpark. Did you nix the stock '78 regulator stuff?

    The pressure and flow specs are really sort of separate things -- at no flow you want the maximum pressure to be in spec (so you don't blow the needle valves open), and at zero outlet pressure the pump needs to be able to deliver the minimum required volume. Have you tried taking the fuel supply hose off of the 5/6 carb and measuring the actual flow volume delivered at zero outlet pressure? You don't want to blow yourself up, but if you measure the time needed to get ~1 liter out of the system I think you could get a decent estimate. I'd also confirm that the flow restrictor is 1.5mm diameter.
     
  4. pcelenta

    pcelenta Karting

    Nov 1, 2003
    216
    steve, that's the info I was looking for. The old 78 regulator was nixed about 5 years ago when it started leaking and the dealer said it wasn't needed. the flow restrictor is what? the small cylinder in the return line? Do you know what the calculation is for line pressure drop?
     
  5. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,055
    I would have thought 6 PSI was the right number pressure wise, 4 sounds a little low.

    The float valve shuts off fuel input when the carb has enough fuel so a couple more PSI prevents undersupply of fuel. As pressure continues to rise, teh float valve becomes a wear issue so just get the pressure up to the point starvation goes away, and then another 0.5 PSI to be on the safe side.

    Since the float valve is regulating fuel into the carb, the flow rate of the pump is not much concern as long as it can pump a whole tank in under an hour at needed pressure (15 Gal/hr at 6 PSI). Sound like you have plenty of pump, but insufficient pressure.
     
  6. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,358
    NY
    Run it at 7 psi and you should have no problems. 4 is to low
     
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  8. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    19,345
    Texas
    Full Name:
    Steve Magnusson
    Paul -- you're taxing my memory ;) -- I can't recall if the flow restrictor is part of the small cylindrical gizmo in the return line from the 7/8 carb to the RH fuel tank or if it's part of the T-inlet fitting itself at the 7/8 carb (i.e., the I.D. of the nipple on which the hose going to the cylindrical gizmo acts as the 1.5 mm diameter orifice restriction).
    I'm not sure what you mean by "line pressure drop" so can't comment...
    Have you tried increasing the regulated pressure to see if the situation improves?
     
  9. pcelenta

    pcelenta Karting

    Nov 1, 2003
    216
    thanks everyone...going to bump the pressure up this weekend and run through the fuel system to check all out. I've heard so much that Webers need low pressure so I set it to 4 psi...guess it's just not enough. Steve, on the issue of line pressure drop...I was trying to figure how much PSI is lost per foot of fuel line...it is probably minimal...but thought it might be a factor...I think there is something to the tune of 5 feet of hose from the pump to the carbs.
     
  10. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,055
    Relative to the 45 PSI to 60 PSI use by fuel injection cars 6-7 PSI is low pressure.
     

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