alright...i have been talkin to a local mechanic about my SF turbo kit on my 2002 civic dx and he was wondering how the SF fuel setup worked (inline fuel pump and vortech fmu...he is a link http://www.7thgencivic.com/mem...age=1 )...i really didnt have an explanation for him cause SF hasnt really told us...i basically just told him that it ups the fuel preasure because the stock fuel pump cant keep up with the positive boost...keep in mind that he hasnt messed with boosted cars before so this is what he was asking.....he told me that most modern cars basically have a high and low setup on the fuel pump...basically when you go fuel throttle the fuel pump steps it up a notch to supply need fuel.... he said that the factory fuel pump should be able to supply more than enough fuel to the car meaning that all you would need is something to control the fuel like a FPR or bigger injectors or a fuel computer of some sort....so why would the factory fuel pump work????? can it just not keep up...why wont it...i didnt have an answer for him because i didnt know....well, i want to know...so those of you who have experience, take a shot at it......


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mechanics are just that.. mechanics, they fix things, not engineer them

never trust just a "mechanic" about performance stuff.

Anyway, that aside, the Inline fuel pump, and the FMU basically work like this.

The in-take fuel pump supply's the inline fuel pump with a high flow, low(reletively) pressure. At lower pressures, this increases the flow somewhat, because the in-tank pump is not working as hard (working at a lower pressure) and the extra fuel volume is compensated by the FPR which is returned to the tank at an increased rate.

The way the engine recieves its extra fueling is by the FMU, basically, when the engine recieves boost pressure, there is a vacuum/pressur signal line connected to it, and there are adjustable ratios of fuel pressure to boost pressures.

Generally FMU's come from 2-12 Lbs of fuel pressure per one PSI of boost.

the FMU/inline pump is a bandaid fix for extra fueling in a turbocharged application.

Often on setups, especially on hondas, you have a nice efficient turbo, coupled with Vtec and good flowing stock heads, and you quickly overcome FMU's even at low boost, since raising the fuel pressure does not increase the fuel delivery enough.

To double the output of injectors, you have to quadruple the pressure, so if you have 200cc injectors (at 43 PSI) to get 400cc flow from them, you would need pressures of 172 PSI of fuel pressure, in addition to one additional PSI of pressure per pound of boost (injectors have to work against intake manifold pressures)

so if you were running 10 PSI, and needed double the flow of stock injectors to supply the fueling (say you were making double the power of the stock motor) (hypothetical now, you'd probably never get away with this) you would need a 14:1 FMU to supply the correct amount of fuel (to reach your goal output of 400cc/min flow)

Most any fuel system unless its extremely well desined with high end pumps wont see more than 130-150 PSI reliably, if that.

I could give more examples etc.. But i think this should help you understand the basic concept.

With an FMU, you still have to be aware of the factory ignition curves, and detonation, and also AFR's, etc.


Brad

 

thank you...i am pretty sure that will answer his ?