SPFI Injector Differences

[SuspiciousPizza]

I've been searching for a new SPFI injector to have on hand when the the pearly gates come calling for my limited stock of used injectors. MPFI injectors are a dime a dozen but new SPFI injectors are more difficult to track down.

The only actual new parts I can find are compatible with the Subaru P/N 16637AA000. However this only seems to be compatible with 1986 and maybe 1987 models. My car is an '89 model which calls for the P/N 16637AA010.

Is there really any difference between the two? It doesn't list 16637AA010 as a supersession part number. But I'd have a hard time believing that Subaru would have one injector only work with a 1-2 year model range. That doesn't sound cost effective.

Why would they change the injector? Different flow rate? Updated spray pattern? Maybe a different throttle body casting? The latter seems very cost ineffective. New molds, tooling, jigs, etc.

The kicker is that 16637AA010 shows it's compatible through the entire SPFI production ('86-'94 here in the States). 

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