fuel injectors

[davidiv]

My freinds civic got spanked by a cavalier . He told me that the guy had a 2.2 ecotec and that he changed the fuel injectors. Any ideas what kind of improvement this makes and what kind and size injectors are good if this works at all.

[Texican]

I'm going to take a stab at this. I'm sure a guru will step in and correct anything I type incorrectly....

The ecu controls the a/f mixture with the help of the water temp sensor, the MAP sensor, the TPS and the O2 sensor(s). It takes readings from all of these items and adjusts the a/f mixture until all of the parameters are at "normal". A larger injector will temporarily run the engine richer until the ECU can adjust to it. Then the car is running at the base a/f ratio again. It depends on the ECU to determine how long it will take to adjust to it. The only time that a larger injector will actually make any kind of real difference is if you're modified enough that the duty cycle of the injector can't keep up with ecu's idea of ideal. Then you start running very lean and very hot.

Just for informations sake, a richer running car doesn't equal power. Stock ecu's "shoot" for an a/f ratio of 10-12:1. Optimal is 14.7:1, but with the constantly changing parameters of the engine, you run the risk of melting your internals when you climb above that. And you can climb above that very easily.

[davidiv]

He also had a cold air intake that might add the air needed for slightly larger injectors. What about same size but better injectors? Are there better ones?

[mthegodfather]

Im gonna guess the guy that told you he had larger injectors didnt know what he was talkin about. Just my opinion but i dont think he had any clue what he was talking about.

[Texican]

Originally posted by davidiv
He also had a cold air intake that might add the air needed for slightly larger injectors. What about same size but better injectors? Are there better ones?

Again, he would need to do some serious modifications to the engine to make the air flow thru it better. Like porting and polishing the head, higher compression, larger valves and much more agressive cams. Or a turbo. A cai isn't enough to warrant the larger injectors. And again, the ecu will compensate for it automatically.

The automakers will use more injector than the car needs, stock, and program the ecu to control the duty cycle to maintain thier ideal a/f ratio (again, something between 10-12:1). This is an insurance policy against burning out the engine while under warranty.

Look at it this way. You'll probably need to add 50-75 horses under the hood before you should even need to consider adding larger injectors. The local dyno tuner will be your best friend; you'll be practically living in his/her shop. When you start seeing the a/f ratio rise above 13.5:1 (consistant across the entire rpm range), you should consider larger injectors.

Now, as for better injectors. I've only dealt with two different makers, Accel and Bosch. You probably already have one of those two. I don't know who makes the gm injectors, but chances are it's one of those two. You already have a damned good injector.