Previa "California Spec" head

[pdgizwiz]

I'm stumped. I'm trolling for some Previa esoteria regarding cylinder heads.

The OEM parts listing thing that I often use lists three different cylinder head assemblies for a '94 2TZFE (NA engine):
11101-79055
11101-79065 (China Spec)
11101-79095 (California Spec)

Only the last one (CA Spec) is listed for the 2TZFZE

Only the first and second are listed for the '93, and only the first is listed for the '92 and earlier.

Not that I want to spend over a grand for an OEM head - it's easy to get a whole Previa for that - but the "California Spec" head appears to be a sort of phased in change in '94, rather than a sharp NA -> SC change. Does anyone know how the "California Spec" head assembly ( -79095) differs from the earlier one (-79055)?
Is the newer head backward - compatible to the earlier NA engines? If not, why not? Or only to the '94 2TZFE?

Thanks

[TheMAN]

nothing is stated in the "new model" guide I have about the cylinder head change
I guess we'll all have to compare the real thing

[pdgizwiz]

Trolling through my '94 FSM for any clues to what changed in the head in '94, all I can find is a slight drop in the lift of the intake cam. Looking at part numbers on line for the cams used in later vans, NA and SC, it appears that an intake cam was used in '94 SC vans that later became "unavailable", where the early cam continues on. Maybe Toyota squeaked by a CA emissions spec by dropping the intake lift, and later found a way to meet the requirement with a programming change? I dunno.

What started this was a hunt for a head to repair my spare engine, on which the head is hopelessly warped. It appears to me that what takes these engines out more than any other cause is overheating due to loss of coolant, either by head gasket failure or other cause. If the van is driven too far with no coolant, the head warps, and that's that. How to get a head, other than to buy a whole van, then? A whole engine (JDM) is the most popular option to fix a van with an overheated engine, but the idea of throwing away a perfectly good lower end runs against my grain. I could buy a used engine from some other Joe, but I'm likely to wind up with another engine like the one I have - good lower end, warped head.

I found a source of rebuilt heads on ebay, for $300. They're listed as being for '94 - '97 though, and the engine I'm working with is from a '93. The "California spec" thing was something that I ran across while trying to find a reason that a '94 head wouldn't work on a '93. I called the seller and was told that the '94 thing was probably a misprint - he knew of no difference. I decided to pull the pin and take the $300 gamble.

The head arrived yesterday. It looks fine. The intake cam has the same lift as the one in the '93 head. I checked it for warpage by pulling out a cam and its lifters and making sure that the cam didn't rock in its journals, something that's clear to see in the warped one. I suppose that if I had a warped head from a Bugatti, I'd find someone somewhere with the skill and equipment to "unwarp" it, but that's not going to happen on a Toyota.

My warped head will go back to the re-builder as a core. They say they'll take them in "any condition". Well, OK, then, here you go...

It will be a while before I get the engine together, and even longer before I put it in a van and fire it up. I'll try to detail some of that in another post.

[TheMAN]

the biggest changes for the S/C engine was cam profiles... they went to 0 overlap.... this sacrificed top end performance for torque... I would imaging using N/A cams with the rest of an S/C engine and the S/C itself would give lots of performance boost
while it's true to an extent that overlap "hurts" forced induction performance, it's a matter of perspective... many high performance turbo engines have a fair amount of valve overlap