Fuel rail and cylinder starvation

Discussion in 'Technical' started by Z32 TT, Nov 1, 2013.

  1. Z32 TT

    Z32 TT Active Member

    so I have my duel feed rails all ready to go and got hose going ****ing everywhere. Im a KISS. Then I actually thought about what i was doing.

    Why is duel feed better? My fuel rail has been drilled out and opened up for flow. If the pressure is there then why wouldnt each injector get its required fuel. only when pressure drops would injectors start to starve.

    Plenty of people have run the stock fuel rail at 400rwkw+. mine has been opened up and I have a walbro 450lph pump that will flow more than my car will consume.

    also with our 6 cylinder engine's stock single entry single exit isnt it basically the same as a supra/skyline/xr6 in line fuel rail (just bent in a U shape). they dont seem to have problems with a single entry exit fuel rail on MASSIVE HP?

    My last paragraph is my biggist argument for NOT going dual feed.
     
  2. Chilledpain

    Chilledpain Z Reaper

    Its just a more even distribution of fuel. That being said, it would probably just cause more even starvation across all cylinders if that was ever an issue. If I was ever to run dual in, dual out, I'd run single an-8, y-piece to two an-6, feed each bank then the same for return. Fuel pump to suit of course. Less cavitation, less chance of starvation and vapour lock.

    In most instances dual in/out would be overkill tho. The theory as you mentioned in the last paragraph is just a theory but many people do it just for peace of mind.

    I think the lack of cooling to that particular cylinder may be more to blame due to the casting slag etc.
     
  3. Z32 TT

    Z32 TT Active Member

    this is the only benefit I can see. and Im going to be seeing a pressure drop on they dyno if this is occuring and know something is up and I dont have enough pump.

    stock ls1 fuels rails have been used at 1000 hp. single entry with 8 injectors and no fuel starvation. If the pressure is there I see that it will be a non issue.

    just hoping someone can point something out if im missing something.
     
  4. Anti

    Anti 14.7 x 14.7 = 44.1

    Watching thread closely

    Interested to see what the starving of cylinder conclusion was based upon
     
  5. SuperZ

    SuperZ Resident Z lunatic

    I would really like to see some comments from Pmack here on this.

    There has to be less resistance of flow regardless of pressure if it flows in both ends - the exact figures I don't know, although I have heard the same figures you mention Z32TT of approx 400kw, suffice to say Pmack has dual feed and has indicated to me it's warranted in having it.

    Who has all the answers here?
     
  6. rob260

    rob260 Administrator Staff Member

    It's a "headroom" thing. Going to be less pressure drop across 3 injectors compared to 6 -however marginal that drop may be. I guess it's a case of the further you push the envelope the less margin for error.
     
  7. BLACK BEAST

    BLACK BEAST SLICKTOP TT R-SPEC

    the purpose of going twin in - twin out fuel rail is for when you are upgrading your main fuel line via hicas line or a dash 8 .

    the volume of dash 8 will supply a -6 line per side equally.



    cant see any starvation in the single feed fuel rail if the stock fuel line is sufficient for your power.

    whats the limit ? can't tell you ....but 400+rwkw I'd upgrade.


    .
     
  8. dieseldave

    dieseldave Well-Known Member

    One of the many reasons why a dual feed to the fuel rail works is that it can eliminate the lower flow at the injector closest to the feed line. When fuel/air/liquid is flowing pass a junction a lower pressure is formed. However, this works in reverse for the end of a manifold for something like the intake manifold on the VG30DE. I am not sure this is making sense, but I have been looking for a video on you tube that will help explain it. better. Might go an make one.
     
  9. dieseldave

    dieseldave Well-Known Member

    Hope this makes sense.
     
  10. Z32 TT

    Z32 TT Active Member

    think my brain just exploded

    So WINFACTORY top feed rails would be off the cards aswell as they are in single entry exit design?
     
  11. Chilledpain

    Chilledpain Z Reaper

    Wow, that is pretty interesting actually. Although the pressure of a garden hose would is a lot different. I might also add that the video shows pressure loss at the end with what would be all injectors open at the same time. This is bound to cause pressure loss an one end. All of the injectors are never open at the same time. Manifolds on the other hand, this would definitely apply to.

    The Winfactory rail has an an-8 feed line (essentially twice the size of stock lines) so the volume of fuel present in the rail and system is substantially increased. Again on assumption, the pressure in the rail itself should decrease very little and the additional volume should eliminate or at least create a buffer for any loss that may occur.

    Someone please correct me if I am wrong.
     
  12. michaelZ

    michaelZ New Member

    I second that. How did he come to the conclusion that the engine is starving for fuel?

    MichaelZ
     
  13. dieseldave

    dieseldave Well-Known Member

    The garden hose experiment applies to both fuel and inlet manifold. Remember that the lower flow to injector (for the fuel rail) or the cylinder valves (inlet manifold)is due to the increase flow.... make sense?
    Bernoulli's principle is that higher flowing fluids are at a lower pressure hence why the first and second have reduced flow compared to the third. A larger rail will reduce this effect, however it stills remains. That is why -8 hoses and top feed rails (or the 300degree style) reduce the effect for fuel rails, as does large inlet plenums for the intake manifolds.
    Whilst the inject flow is a pulse at low RPM when the duty cycle is lower, which brings its own issues, at WOT the flow is almost a constant stream due to the duty cycle being close to 100%. Inlet manifolds are different, but do have the same affect, that is exaserbated by the VG30DE manifold design especially for number 5 and 6 cylinder. This is another reason these cylinders run lean when on the limit.
    If you understand the theory you can counter it.
    This is how I did it on the E-Vades by having separate in and out to a central regulator that is a diaphragm type to act as a accumulator (remove pulses).

    Road
    [​IMG]
    Race
    [​IMG]
    The difference being the size of the fuel rail. But both at feed by -6 hoses.
    Is any one still reading and finding it useful?
     
  14. BLACK BEAST

    BLACK BEAST SLICKTOP TT R-SPEC

    winfactory although single in and out is a spider leg design unlike stock

    plus as stated its 8an

    entry is closest to 5 and 6

    good or bad thing ? can't really tell you

    [​IMG]
     
  15. Z32 TT

    Z32 TT Active Member

    Yeah seems like bde would be the best rails to follow dieseldaves theory.

    Hmm all very interesting.
     
  16. tassuperkart

    tassuperkart Its a lie I tell you!

    Look, what Dave has shown is correct and fair, in relation to a 1/2" garden hose and 6mm nozzles at 100% open time.
    Perhaps try 1mm nozzles with the same hose and delivery pressure and I think the test results might be very different!

    In the world of high pressure fuel delivery and such low flow in relation to the manifold (rail) size and factor in such short injector opening time (Circa 20Ms max)... well think about it.

    The inlet manifold is a different story and thats largely due to design constraints.
    A better designed plenum will deal with the issue.

    newhoo.
    E
     
  17. stumagoo

    stumagoo Active Member

    another point to add is most the time our injectors are not firing together, they may be pretty close together though, - not sure how much this would effect the result
     

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