STI Injectors

imprezton · 12-31-2002, 02:36 AM

Okay, 550cc injectors on EBay. Are these plug-in for the 2.5 as well?

Will the stock ECU adjust to the fuel flow? And if they are plug-in, and the ECU will adjust, will I need a higher volume fuel pump? my CAI and Home Depot Airbox Mod leaves me feeling a little lean lately. I just wonder if this is a path to righteousness

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imprezton · 12-31-2002, 11:22 AM

badump-bump

DrBoy01 · 12-31-2002, 12:53 PM

I'm almost 100% sure that the STi injectors would have to be coupled with an aftermarket ECU or maybe a S-AFC-type device in order to gain any benefit at all.

Otherwise, how would your ECU know that you actually had the capability to increase fuel flow? :P

mrbell · 12-31-2002, 02:06 PM

It's not really a matter of "how would your ECU know that you actually had the capability to increase fuel flow?"
it's more of a question of "can the ECU hold back enough on fuel"
There are two types of injectors. High impedance and low impedance. Most(if not all) stock injectors are high impedance. This means for a certain range of voltage, they open a certain amount(low impedance injectors open all the way for a certain amount of time, based on supplied voltage or not). These voltage levels are industry standard so whether it's 550cc or 280cc, a certain voltage will open it a certain percent. The problem is that if your ECU is built around a parameter saying that 280cc/min is max, then say at cruise you're using 25% of that you're pumping 70cc/min which is much less than 138cc/min that a 550 injector would use. The ECU can detect rich/lean conditions so it can pull back on the fuel... can it pull back enough? That's a problem...
btw, 25% was just an example, and I don't know how well 550's will work in a 2.5L motor w/o some sort of external controls. Also, I don't believe the WRX uses the same injector form factor(top feed v. side feed) that the RS uses, so they may not even fit in there at all...

12-31-2002, 02:36 AM	#1
imprezton Scooby Specialist Member#: 22958 Join Date: Aug 2002 Chapter/Region: SWIC Vehicle: 2008 She cheat me and taked my salts!-Crees	STI Injectors Okay, 550cc injectors on EBay. Are these plug-in for the 2.5 as well? Will the stock ECU adjust to the fuel flow? And if they are plug-in, and the ECU will adjust, will I need a higher volume fuel pump? my CAI and Home Depot Airbox Mod leaves me feeling a little lean lately. I just wonder if this is a path to righteousness * Registered users of the site do not see these ads.

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12-31-2002, 11:22 AM	#2
imprezton Scooby Specialist Member#: 22958 Join Date: Aug 2002 Chapter/Region: SWIC Vehicle: 2008 She cheat me and taked my salts!-Crees	badump-bump

12-31-2002, 12:53 PM	#3
DrBoy01 Scooby Specialist Member#: 20444 Join Date: Jun 2002 Chapter/Region: MAIC Location: Wilmington, DE\|Berkeley Vehicle: 2006 Outback 2.5 XT Garnet Red Pearl 5MT	I'm almost 100% sure that the STi injectors would have to be coupled with an aftermarket ECU or maybe a S-AFC-type device in order to gain any benefit at all. Otherwise, how would your ECU know that you actually had the capability to increase fuel flow? :P

12-31-2002, 02:06 PM	#4
mrbell Scooby Specialist Member#: 1871 Join Date: Jul 2000 Location: Salt Lake City, UT Vehicle: 2000 Impreza 2.5RS Blue Ridge Pearl	It's not really a matter of "how would your ECU know that you actually had the capability to increase fuel flow?" it's more of a question of "can the ECU hold back enough on fuel" There are two types of injectors. High impedance and low impedance. Most(if not all) stock injectors are high impedance. This means for a certain range of voltage, they open a certain amount(low impedance injectors open all the way for a certain amount of time, based on supplied voltage or not). These voltage levels are industry standard so whether it's 550cc or 280cc, a certain voltage will open it a certain percent. The problem is that if your ECU is built around a parameter saying that 280cc/min is max, then say at cruise you're using 25% of that you're pumping 70cc/min which is much less than 138cc/min that a 550 injector would use. The ECU can detect rich/lean conditions so it can pull back on the fuel... can it pull back enough? That's a problem... btw, 25% was just an example, and I don't know how well 550's will work in a 2.5L motor w/o some sort of external controls. Also, I don't believe the WRX uses the same injector form factor(top feed v. side feed) that the RS uses, so they may not even fit in there at all...