Stan Weiss wrote:
cjperformance wrote:When running as blow thru you need to remember that the fuel inlet pressure may be higher than 4-6psi BUT this pressure will be relative to the boost pressure that is inside the fuel bowl. IE- if you run 10psi boost in blow thru form then to maintain a relative fuel pressure of say 6psi you need 16psi in the fuel line. In this instance the needle and seat only sees this ar 6psi ( the difference between bowl pressure(from boost) and fuel inlet pressure.)
As Joe says, too much pressure is not so good with a carb. The more pressure thru the needle and seat, the more fuel foaming/airation will occur which is BAD for maintaining an accurate feel curve. If you cant get enough fuel flow in there with 5psi in the line, then you need to rework the fuel system to flow more fuel at 5psi.
Shouldn't this be done with a boost reference regulator and not running the higher pressure all of the time?
Yes Yes Yes, I didnt go that far into it but should have.
Most definetly, The fuel pressure must constantly be referenced to boos pressure.
ie, for a 6psi relative fuel pressure the referenced reg/pump/whaterver controls your fuel press will maintain a 6psi difference, usually starting with say 6psi from intake vac thru to boost, then 1psi boost will give 7psi fuel, 5psi boost will give 11psi fuel, 20psi boost will give 26psi fuel and so on.