fuel system differences between FI and NA?
Thread Starter
TECH Resident
iTrader: (3)
Joined: Mar 2002
Posts: 919
Likes: 0
From: wilmington delaware
fuel system differences between FI and NA? from what ive been reading on the FI forum you guys are swapping to much bigger injectors than most of the na or even the nitrous crowd. does boost have different requirements than an na motor with the same power? for example, the stock 28lber's or svo 30lb injectors are good for most cars under 500rwhp na right? but boosted 500rwhp motors have much bigger injectors? do i have this right? if so, why? i know better safe than sorry but is it neccesary or safety?
Moderator
Joined: Nov 2001
Posts: 3,048
Likes: 12
From: Raleigh, NC
Re: fuel system differences between FI and NA? It/s is both... neccesary AND safer! <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
Nitrous creates it's own form of explosion in the cylinder, right? Ozygen get's released and the resulting force is greater than NA. I think the fuel needs are still a bit greater, though, for the higher HP applications, right?
Anyway, we FI guys are packing WAY more air into the cylnders, and the proper fuel mixture must be maintained, still. So we need larger injectors or need to make them work more, and need a fuel pump that will keep the fuel pressure we need up to par.
Big Cube NA motors need more fuel, too... maybe not what FI guys do, but the need is there.
That's a layman's "simple" spin. I think you have some tech-mechs haning out around here who can give you a more technical perspective. You also may get a good anser in the engine section, where some of those guys have run big-cubemotors AND FI AND Nitrous at ome time or another, or in combination. <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />
Nitrous creates it's own form of explosion in the cylinder, right? Ozygen get's released and the resulting force is greater than NA. I think the fuel needs are still a bit greater, though, for the higher HP applications, right?
Anyway, we FI guys are packing WAY more air into the cylnders, and the proper fuel mixture must be maintained, still. So we need larger injectors or need to make them work more, and need a fuel pump that will keep the fuel pressure we need up to par.
Big Cube NA motors need more fuel, too... maybe not what FI guys do, but the need is there.
That's a layman's "simple" spin. I think you have some tech-mechs haning out around here who can give you a more technical perspective. You also may get a good anser in the engine section, where some of those guys have run big-cubemotors AND FI AND Nitrous at ome time or another, or in combination. <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />
Re: fuel system differences between FI and NA? also there is the "delta pressure" i think it's called. Anyway, the boost in the intake is also pushing against the end of the injector trying to keep the fuel from coming out. You either run more fuel pressure to overcome this or bigger injectors to get the same amount of flow as you'd have with a n/a motor. If I were starting from scratch, i'd get the svo 42# injectors ...a good fp regulator and a walbro 340 as minumum.
Re: fuel system differences between FI and NA? BSFC is commonly higher in a boosted application, so more fuel is required for a given power level.
And working fuel pressure is a function of boost pressure. Higher working fuel pressures require a pretty stout pump, as flow drops with increased pressure.
Also, we tend to run a richer A/F for peak power and saftey than the NA crowd. 12.5:1 is about as lean as most want to go for piece of mind.
All adds up to a bigger fuel system requirement.
And working fuel pressure is a function of boost pressure. Higher working fuel pressures require a pretty stout pump, as flow drops with increased pressure.
Also, we tend to run a richer A/F for peak power and saftey than the NA crowd. 12.5:1 is about as lean as most want to go for piece of mind.
All adds up to a bigger fuel system requirement.
