air/ fuel

[austinasto]

okay, if you put more air in your car than you need more fuel too. so if i upgrade my fuel injectors to 310cc with my injen cold air intake I shoould be ok?

[navylife59]

For a given amount of air, your engine needs a given amount of fuel to remain stoichiometric. Adding more airflow should equate into more fuel by the ECM. This is not always true and is only up to a certain point. Once the injectors have reached saturation (over 90% Duty Cycle), the ECM is not able to add anymore fuel. Upsizing your injectors will lead to poor performance as the computer needs to know what size injectors are installed. The injectors will send too much fuel into the runners making the engine run rich at times, causing rough idle. The OEM injectors are 380cc. I have 550cc injectors but my computer is tuned for the TRD S/C kit with the 440cc injectors. My car runs rich all of the time, even though, I am running 15lbs of boost.

[austinasto]

Ok. I have headers, and cold air intake. I'm trying to get the most out of my stock motor as possible. If I get bigger injectors, will a aem fic help control the fuel

[CadenceScion]

A stock N/A tC won't benefit from bigger fuel injectors, the OEM injectors do plenty fine. If you want to get more out of the engine upgrade to F/I (TRD Super Charger or a Turbo Kit), either route you'll have to upgrade the injectors as well as the fuel pump, your octane rating and swap the CAI for a short-ram intake.

[navylife59]

You know there are those that claim 10-15WHP with a UniChip on a purely stock motor.

[mtnbk]

And there are those that claim that their votex generators, magnetic atom aligners, and water injectors do wonders as well. Ignore all of them. Learn first the principles involved.

Your Injun CAI does not put more air into the intake. It only marginally reduces restrictions to allow the pistons retracting on their intake strokes to more easily pull air in. But the maximmum amount that'll go into the intake is the volume the pistons can pull in. Ignoring filter, turbulance, port, and valve restrictions, and since the engine has a 180 degree crank, at any given time only one piston will be on the intake stroke pulling air in. The others will be in the combustion stroke, the power stroke, and the exhaust stroke. Therefore, the total amount of air being drawn in at any given moment will be no greater than 1/4 times the engine displacement times the redline rpm. Since the path is obstructed by the port size and the valve, and since the amount of air being drawn in is subject to the cam profile (the valve opening and closing), it's reasonable to use 70% of the aforementioned derivation.

Since 14.7:1 is the ideal air to fuel ratio, if you do a bit more math, you'll find that the stock injectors have enough capacity to feed the engine's capability to draw air in, sufficiently to maintain the proper air/fuel ratio.

It's only when you begin to push air into the intake, with a turbocharger or a supercharger, that you need to consider larger injectors. A ram air system could drive the injectors past saturation if it were designed to make maximum use of the rammed air, but I can tell you that if you use reason in its design you can add more air without overrunning the capacity of the injectors.

Getting back to my second paragraph. I said "marginally" because all it really does is increase the intake diameter some, eliminate the carbon filter in the stock airbox, eliminate the turbulance of the stock airbox, and replace the OEM filter with a wetted cone filter....which probably is as restrictive as the OEM filter. It actually takes the air from the same chamber as the OEM snorkle, the left fender cavity.