Re: Some details of the 2AZ-FE engine

>>
>> Toyotas have been using aluminum heads for as long as I can remember.
My
>> first Corolla, a '74, had an iron block and aluminum heads, which
worked
>> well for them, but was a fatal combination for certain Chevy (VEGA) 
>> models...
> 
> Actually Vegas had aluminum blocks and cast iron heads! One of the 
> stangest combinations ever.


Similar combination to the '62 Chrysler 225 slant-6 (aluminum block 
version). Cost and manufacturing considerations necessitated the use of 
a common iron head on both the die-cast aluminum block and the 
simultaneously-produced iron block version of the 225. The aluminum 225, 
unlike the first iteration of the Vega engine, did have cylinder liners. 
Both were, as you noted, open-deck designs with free-standing cylinder 
bores.

Later, the notorious Cadillac HT-4100 4.1L v8 of the 80s used cast iron 
heads on an aluminum block also. The failure of the 4100 really doesn't 
say anything bad about iron heads on aluminum blocks, per se. The 
slant-6 had relatively little trouble, although people who build them 
today for restoration (and occasional racing- the bare block can be 
hauled around one-handed!) note that it doesn't have a lot of margin for 
high cylinder pressures and doesn't take well to much boost or any 
detonation. But the stock ones held up just fine, and there are a 
surprising number out there still running around (sometimes with the 
owner completely unaware that its an aluminum engine). But conceptually, 
it really is a little backwards to build a light aluminum block and then 
penalize it with a pig of an iron head. If you need iron, it makes more 
sense to use it in the BLOCK where the extra strength is most needed, 
and that's why there are so many iron block/aluminum head engines still 
in production. And looking back to the first poster quoted above, I 
can't think of ANY iron block/aluminum head engine that proved to be a 
"fatal combination." I know a lot of people believed it was going to be 
awful when they first started appearing in the 70s, but in practice it 
worked just fine with the correct choice of head gasket material to 
allow for the differential expansion. Heck, my wife's iron 
block/aluminum head Chrysler 3.5 has 260,000 miles and has never had the 
heads off (or anything deeper in than the intake plenum gasket, for that 
matter).


My memory of the Vega's problems pretty much agrees with yours- the main 
flaw was the lack of rigidity of the block itself, allowing the 
cylinders to "go egg shaped" with the slightest overheating (or even 
normal spirited/agressive driving), resulting in huge oil consumption 
and of course power loss.