Technical > Spud Miller's Cave

fuel pressure question for Spud

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wideopen231:
 Hopefully I can explain this properly.
 Looking for educated guess on pressure for part of fuel system.
 80 a pump 6.78 gpm
 main jet normaly 130 using 8 x.038 nozzles
cube enderle BV
 With new system I would have 115 and 65(close numbers maybe not dead on) jets both low pressure poppets operating as one main jet.Would run system this way to get better dialed in before getting to next step.
  the 65 jet would be bypass that in a valve of my design,should be free flowing for jet size.Under normal operation it would return to tank.Under nitrous use its enrichening system,jetting figured to be slightly more then the .065 bypass.This will be operating roughly  within 500 rpm range 6500 to 7000. Real word testing will help zero in on exact range.

 Not asking about nitrous just fuel pressure that would be on other side of the .065 jet at this rpm range. Oh yes this would be T'd in before BV and according to your calculator shouls have system pressure 93 psi. Not sure if enough info or if question can be answered w/o flow bench in even a SWAG. Not looking for dead on just good ballpark number.  Mainly check calculation and fuel pressure flow for nitrous based on pressure. I have fomrulas to convert flows based on pressure and vice a versa if know one or the other.

 Any idea?      Sorry if hard to follow explanation.

Spud Miller:

 Not sure I'm following all that...sounds like the question is:

 "fuel pressure that would be on other side of the .065 jet at this rpm range."

 If you're wondering what the pressure is on .065 pill's check valve at a particular engine speed (to know where to set it so it'll be open), I'd say the only way you'll be within 5 PSI would be to test it on the flow bench. And if you change ANYTHING (any of the nozzles, any pills in the system), it'll be different. Because of the difficulty in determining some exact pressure there (without a data logger of course), I'd suggest using an electronic valve (one of these would work super: http://fuelinjectionent.com/webstore/product_info.php?products_id=181).

Just use an RPM activated switch to turn it on or better yet a window switch (to turn it on and off) and the .065 pill will only ever bypass fuel between 6500 to 7000 RPM no matter what you do to the fuel system.

Spud

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