So... if I were to buy a 99/00 head casting, could I drop my HLA cams, valves, springs, HLA's, etc in there and just run it? I know people usually go the other way, but I'm stubborn.

My GTR head has really restrictive intake ports, but it has sodium filled exhaust valves which I'd like to keep. I have HLA performance cams, so keeping those would be pretty cool too. I know the valves would have to be lapped in but other than that... wouldn't it all just drop right in?

Thanks

 

Yes

 

Question here, since it's been a while since I looked at a bare NA block.

On the NB engine, there is a restrictive orifice pressed into the passage (at the deck) which supplies oil up into the head. Do the NA blocks have this same restrictor? I can't recall seeing one the last time I had the head off my '92, but then I wasn't really looking for it.

I'm assuming (based only on my own speculation) that this was added at the same time they switched from HLAs to solid lifters, based upon the reduction in demand for oil flow and pressure in the head. IF this is true (and I don't know if it is) then I'd expect HLAs running in such an environment to be problematic.

 

If you mean on the deck surface, I don't recall seeing anything on my 94 block. Also though, like you, I wasn't looking for anything.

 

Every 4 cyl motor I have ever rebuilt has this "orfice". It is there to regulate OP in the head. To be more specific, Both 1.6 and 1.8 motors have it, as well as every 4cyl honda motor the land of the rising sun has ever given us.

 

so i guess what your saying is it would be worth taking a look at the size of this orifice, and possibly enlarging it to the size of the one in the HLA head if it is in fact different? sounds like a piece of cake to me. i may go this route... haven't decided yet.

i would prefer to keep the long block "unopened", but i'm afraid i may have already maxed out the GTR intake ports....

 

Gotcha. Its function is pretty obvious, I just didn't know whether it was added to reduce oil pressure at the head with the elimination of the HLAs.

Prior to getting into Miatas, most of my hands-on 4 banger experience comes from the ACVW world. I can assure you that they most certainly do not have such an orifice. Of course, they don't have positive-pressure oiling to the head, either.

I wouldn't.

The orifice is in the block, not the head. The process of drilling it would drop a lot of metal down into the oil galleys of the block, with no way to get it out short of a complete bottom-end teardown.

Actually, there's no need to even look. I just checked the parts catalogs, and in both the '95 and '01 books, they have the same P/N: B366-10-305. And Neo is right, the '91 catalog has the same part too.

Here's a picture of where it goes:




Carry on.

 

This sounds cool.

But I have to ask, well.. why? You aren't doing this out of necessity since you don't have the 99/00 head yet, correct? This is still intriguing since its an unusual mod... what do you mean when you say "HLA performance cams?"

I'm not saying this is a bad idea at all, if you have stronger cams than a 99/00 + the sodium filled exhaust valves, it should be a sweet combo! Just curious.

 

Necro. I'm coming to the last couple of steps in my engine build process. This info helps, as I'm doing the BP to BP4W head swap on my 97 block. However, my engine builder wanted me to find out if anyone in high rpm race/track/autocross application restricts this block/head oil passage even more than factory. The thinking is that at high rpm, the pump may flow out a lot of the sump's capacity into the head, and could lead to starvation. What do you guys think?

He's coming from Chevy SB/BB thinking, apparently every switch from hla to solid in race applications brings about a switch to a smaller block to head oil orifice.

BTW, thanks as usual Joe for the smart info from the fsm.