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Discussion Starter #1
I'm in the process of installing a turbo kit on my car. The mechanical aspect was easy for me but now that fueling has come into the picture I have a ton of questions.

The only thing that I have so far are some 550cc injectors which i got for free. Those should provide more than enough fueling for my needs (goal of a reliable 200hp track car) and I plan on upgrading my fuel pump. So do I need a FMU? Is it easier to tune with one?

I'll leave engine management for another post. #-o
 

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You really do not need to upgrade the fuel pump if you use a good piggy back or stand alone. With those injectors, I would not increase the fuel pressure because those will most likely drown out the motor with fuel. When I say a good piggyback, I mean like a xede, and EMU might be able to idle those injectors, but you would really be pushing the envelope. Just get good engine management to get the car running, and I wouldn't be running an FMU with those injectors though. Just my .02 to help you out.
 

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Discussion Starter #6
So would an FMU be used on low boost vehicles that might chose to stick with their stock injectors?
 

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well i use 1.8L injectors with a begi fmu.

im running roughly 7psi right now. my idle fuel pressure is roughly 40psi. when i go under boost with the stock fuel pump i rise to 80 psi which supplies enough fuel through the 1.8L injectors, which are approx. 245cc.

Scott
 

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i use 440CC RC injectors at 200hp, my duty cycle for my injectors is only 60%, i do have an electronic fuel management controller though, but do not run the vortec thingy. if your injector duty cycle is close or nearing 80% then you might start to having problems.

simon
 

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the only reason for a FMU is to squeeze more fuel out of smaller injectors. The reasoning...increase the fuel pressure at the rail, increase the flow of the injectors.

or the square root of the (new rail pressure / old rail pressure) x injector CCs = new CCs
example: SQRT(100psi/43.5psi) x 203cc = 307cc

what that means is if you run the stock 1.6L injectors at 100psi of fuel with an FMU they will technically be 307c injectors, which could support about 175BHP

There is no point to an fmu for the 550s. At 50psi (rail pressure at 0~hg.) those injectors can flow enough fuel to support about 325BHP.

However, since you have 550s you will need something to even idle them, the stock ecu will not be up to the task.

One thing to remember, the stock pump can flow enough fuel at 50psi to support about 300BHP.
 

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yeah it can happen, but the computer can only do so much with them.

FWIW, im currently running 305cc injectors with the stock aFM, it didnt take much for it to work.

the problem is after the ecu reached about 5500rpms.

it no longer using the signals from the AFM to determine the mixture.... it simply fuels off an internal map.

so whatever it would normally throw at the 203cc injectors it will do to the 305cc injectors, which means, lots of extra fuel you cannot control.

then that means you have the percisely tune the fuel pressure so it doesn't happen. it can be done.

put in too large of an injector and the corrections are harder for the ecu to make, since it still thinks it's making corrections on a 203cc injector.

but since you could easily fuel about 250rwhp with 305cc injectors and 100psi, there really isnt a need to go much bigger with a FMU setup.

the 1.8L injectors (265cc) have proven to fuel a good 190-200rwhp at 100-110psi as well.
 
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