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I'm big on using the search engine before asking a question that has probably been answered 10 times already but I've been searching for couple hours now and not getting a conclusive answer hence the post. I apologize ahead of time if it's here somewhere and I just didn't search well enough. Also apologize if this wall of text is too much info or rambly just trying to be thorough.

I have a 99 ex manual 280k with bad valve stem seals (smokes after decel in gear) and pretty sure a head gasket going (oil in coolant but not coolant in oil) used 3 gallons of oil (1qt every half tank ish) driving round trip Medford, Or to Dallas, Tx yikes I know. Head stamp is p2j-3 date stamp 98 with a p2p-itp-4 intake which has the nipple in the manifold which should mean it has the air injection holes (thought that was 99-00 only tbh, but yet to yank head to verify if holes been plugged or not)

I ordered all the gaskets and seals to rebuild a head from honda, but my landlord is less than accommodating and gave me a bunch of crap for doing my brakes and swapping the coilovers so I have a feeling a top end rebuild won't go over very well (I'm a diesel mechanic for over 10 years and class a truck driver so it's not like I have a problem with diy, but he doesn't like the idea of people working on their cars here...) so I figured I'd hop on the ol' facebook marketplace and grab a head I can send to the machine shop for resurfacing and replace the valve stems and such and quick swap a head before the landlord can notice. Ended up grabbing two heads among a bunch other parts from a guy emptying out his garage for cheap.

Both the heads came off y8 blocks which i got as well but theres a subtle difference with the IM mounting surface that's confusing me.

Head #1 stamped p2j-3 date 96 has a different mounting surface for the intake manifold (which did not come with it) compared to the other head I acquired.

Head #2 stamped p2j-3 date 98 has what looks like a channel on the mounting surface which head #1 does not have and it did come with an intake manifold stamped p2p-itp-2 which does have the injection holes

I know 96-98 is not supposed to have the air injection holes on the manifold that 99-00 did, but I assumed the head cast was the same 96-00 seeing as remanufactured y8 heads sold on the internet don't differentiate between the years like the manifolds do.

So my main question is why are the mounting surfaces quite different?

Secondary question is why does the 98 head #2 have the injection holes & I assume the one on the car also has the air injection holes with them being 98 date stamped, best guess here is they are late 98 manufactured to 99 spec?

I don't want to rebuild the wrong head and I'm thinking I'll most likely go with the head#2 as it is likely closer to what's on the car now but that IM mounting surface difference really has me scratching my head.

Yeesh, I know that was long winded sorry.... also thanks in advance to anyone who read all that and can clear up why these two heads are quite different and why the 98 heads appear to have air injection.

Head#1
Head#1.jpg

Head#2
135763

Head#2 intake
135766

Head on car
135764
 

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93 Civic HB SI
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The reason there are two versions of intake and head, is because Honda felt the need to have injector air injection on some engine models, while others didn't.

Just different flavors of emissions and efficiency strategies.

This type of air injection system was NOT designed for catalyst warm up, but to direct a secondary charge of air directly at the injector tips to improve fuel atomization and vaporization. You can see the tiny holes in the head aimed right at the spot where the fuel injector would be spraying.

This system only allows air to flow through this secondary passage when coolant temp is below 150°F by use of a thermally activated valve, and the goal is to try and improve emissions and efficiency during warmup on some flavors of D16Y8.

I'm not really sure why some Y8's got it and others don't. Probably some kind of OEM CAFE deal, although Honda's never had a problem meeting their fleet average fuel economy, or for sale in states like California or similar states or countries that model their emissions regs like cali.

OEM's dont do these kinds of things and introduce this type of variability unless they absolutely have to, so while I honestly have no clue why there is this variability across the Y8 family, Honda had to do it for a damn good reason.
 
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