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Okay here is a question I have been trying to find information about, but nobody seems to have the correct answer.

When people talk about a fuel injector's flow rating they normally describe it using the cc's which im guessing is cubic centimeters.. for example 315cc, 440cc, 550cc... etc. Now in some cases people say that the flow rating is determined only by the fuel pressure while some say it is the voltage sent by the ECU. This is where my question comes in... which is which..

For example, from what I have heard the stock early model 3s-gte injectors were rated at 440cc and the later model 550cc. Some people say if you were to put the 550cc injectors on the engine without raising the fuel pressure to that of the later model engine... the injectors would only yield a flow rate of 440cc... or something else.

Wouldn't having the bigger injectors flow more fuel no matter where the fuel pressure was at? With the ideology that injector flow is controlled mainly by fuel pressure... you could say that if you ran the right pressure, and the injectors ran off of the same voltage... you could essentially put 550cc injectors even on a stock 4age engine and not run rich... which I think is false... so which is it???
 

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dirtdilla said:
Okay here is a question I have been trying to find information about, but nobody seems to have the correct answer.

When people talk about a fuel injector's flow rating they normally describe it using the cc's which im guessing is cubic centimeters.. for example 315cc, 440cc, 550cc... etc. Now in some cases people say that the flow rating is determined only by the fuel pressure while some say it is the voltage sent by the ECU. This is where my question comes in... which is which..

For example, from what I have heard the stock early model 3s-gte injectors were rated at 440cc and the later model 550cc. Some people say if you were to put the 550cc injectors on the engine without raising the fuel pressure to that of the later model engine... the injectors would only yield a flow rate of 440cc... or something else.

Wouldn't having the bigger injectors flow more fuel no matter where the fuel pressure was at? With the ideology that injector flow is controlled mainly by fuel pressure... you could say that if you ran the right pressure, and the injectors ran off of the same voltage... you could essentially put 550cc injectors even on a stock 4age engine and not run rich... which I think is false... so which is it???

That is what I've heard. The bigger injectors will flow more. I've heard that if the voltage drops too low, then the car might not start/run.

You can use a fuel pressure regulator to simulate a larger injector. If you adjust the base fuel pressure, then the injector will flow more throught the rpm range.

At one time or another I was thinking of running larger injectors, but dropping the base pressure to simulate smaller injectors. From what I was told, it may work depending on how low I would go, but the fuel rail might cause lean problems due to having too little fuel at one end of the rail.
 

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Actual fuel flow is determined by:
Injector flow rating;
Injector pulse width ("on" time, determined by ECU);
Fuel pressure.

The injector rating is at whatever fuel pressure the injector manufacturer stipulates, and assumes 100% duty cycle (always open).
 
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