Injector Question. [Archive] - Forum


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10-12-2008, 01:18 PM
I know this is a somewhat retarded question here, but is it possible to have injectors that are TO big, and what I mean by that statement is, that put to much fuel per hour?

I am looking at upgrading to 42.5 LB/HR injectors from Milzy Motorsports. Now, my engine is stock for now, but to my understanding, the injectors will only throw in as much fuel as they are told to by the computer, correct? Even if I stomp it, they will only give the amount of fuel the computer tells it to, right? I assume this is the case, it is just the injectors have the potential to do much more fuel flow in the future when the engine is beefed up.

Thanks for the help.

10-12-2008, 01:32 PM
Yes, it is possible to have too big injectors. If your engine is mostly stock you do NOT need 42lb injectors. If your engine was still NA even if you had a cam, heads, raised compression, etc etc they would probably still be too big. The most you'd need are 28lb'ers or 36lb'ers. You don't need to worry about switching them until you get a lot more mods though. Right now it would just be a waste of money. The stock injectors will give you enough fuel for basic mods.

I'm running 42lb injectors with 9psi of boost and they are still almost too big. The injector pulse at idle is very short, and at WOT they aren't even running 80% duty cycle. I'm actually thinking of dropping down to 36's because they have a better spray pattern at idle. The type of injector (pintle or disc) and the spray pattern they make can affect your drivability and gas mileage. There is a limit to how fast an injector can open and close. If the injector is too big for how much air your engine is pulling at idle, the pcm can't open and close it fast enough so it will have trouble maintaining the AFR and you'll get poor fuel atomization. Rough idle, less mileage, and even damaging the O2 sensor and catalytic converter can result if it's extreme.

Basically, you want only as large an injector as you need to provide enough fuel at peak throttle and rpm, and not much more.

10-12-2008, 09:27 PM
Thanks for the great reply, was very helpful and explained very well!