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This maybe one for Badger5? limitations of A3/S3 fuel lines, rail etc

Discussion in 'A3/S3 Forum (8L Chassis)' started by Andrew@A.L.D, Jul 24, 2012.

  1. Andrew@A.L.D
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    Andrew@A.L.D Cylinder Head Master

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    [Jul 24, 2012]
    I'm just thinking out loud

    When going for big power people will normally fit a inline pump, maybe a 4 bar fuel pressure regulator and/or bigger injectors but thats ok unto a limit i'm sure but what are the limits of the standard fuel rails, fuel lines and a inline pump as a guide line.

    I was thinking of changing mine in the future as Bill said i will be trying to push lots of fuel though a 6mm fuel line if i up my line pressure to get over 540bhp and would need to check the pressure at the rail.

    If i was to fit a swirl pot feed by the S3 pump then use the bigger fuel line from that to the 2nd pump and bigger fuel line to the rail with a modified inlet on the rail or aftermarket one would that be safe and i take it the 6 mm return is ok i assume?

    now if i change my 870cc to 1000cc would the standard stuff still be ok as i wouldn't need to run higher fuel pressure?

    I know some will say why fit a swirl pot, well it could work out cheaper to do it that way as 1000cc+ aren't cheap.

    As said i'm just thinking out loud?
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  3. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Jul 24, 2012]
    The S3 pump can only flow so much fuel, if it cant keep up in series as it is just now, a swirl pot isnt going to help you. It might give you a short time buffer, but keep using more fuel than the in tank pump can deliver and you'll run the swirl pot dry.

    Folk with S4/RS4's seem to manage >600hp without touching the OEM fuel lines, though i'm not sure if they're the same size as the ones on the A3. The typical approach on the S4/RS4 models is a bosch 044 mounted in the tank, rather than two pumps in series. Less to go wrong that way.

    Bear in mind that the return line has to flow ALL the fuel that isnt used. So if your pumps chucking out 5 litres a minute, and your engines only using 0.001L per minute as its sitting idling, then that return line needs to be able to cope with everything the pump can flow. If it acts as a restriction, the fuel pressure will start to rise.

    if the smaller return line can handle transporting all the fuel back to the tank currently, then i cant see why the larger feed line would pose any issues.
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  4. s33nyboy12
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    s33nyboy12 Well-Known Member

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    [Jul 24, 2012]
    Very interesting, a point most people would over look.

    I have a question..... I was sat behind a 200sx erlier with driftworx written all over it pulled alongside him in my transit workvan and asked him what he's running ect. After a lot of chat chat chat it started blue smoking sat at the lights to which he said " damn thing, only problem with these constantly over fuelling! " it did stink of fuel too

    What I'm getting at is would his over fuel be down to similar his fuel return cannot cope and therefore on idle the engine is overfueling ready for "big boost" moments.

    Off topic I know sorry , just wondered.

    Cheers, Sean
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  5. Andrew@A.L.D
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    Andrew@A.L.D Cylinder Head Master

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    [Jul 24, 2012]
    Blue smoke could be a number of things but if he said it was over fuelling then he will be getting bore wash, the extra fuel is washing the oil away from the cylinder wall glazing the bore and wearing out the rings.

    If its over fuelling then his AFR will be out and the only way to sort it would in need of mapping
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  6. Lizard-Racing
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    Lizard-Racing DTM

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    [Jul 24, 2012]
    Standard fuel lines here
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  7. Andrew@A.L.D
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    Andrew@A.L.D Cylinder Head Master

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    [Jul 24, 2012]
    Whats the full spec of your fuel set-up lizard?
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  8. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    [Jul 24, 2012]
    mines a race car, and I have spec'd it accordingly..
    there was a great discussion over on vortex not long ago where fuel line size came up and a whole bunch of calcs came up which support larger lines being the right thing to do.

    mine, for ref is S3 in tank pump feeding 2ltr swirl pot off which feeds 2 x 044 pumps in parallel (redundancy) and join into a -8 fuel line to front of car, into rail #1, then into rail #2, then into aeromotive fpr and returns to swirl pot in -6 line (which from what I have read since should be same as feed line -8.... no adverse effect on mine however as is, and my fuel pressure is logged by dta ecu)

    have a search on vortex 1.8t section for fuel line size.
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  9. Andrew@A.L.D
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    Andrew@A.L.D Cylinder Head Master

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    [Jul 24, 2012]
    Thanks bill
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  10. Westy
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    Westy Double Dark Side! Diesel & 8P

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    [Jul 24, 2012]
    I haven't a clue what anyone has said in this thread but it's still very interesting to learn new things.
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