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Are all ea81's the same.

No

-Some had tappets, others had hydraulic lifters.
-There were 2 variations of heads, with some having the exhaust valves towards the centre of the head, (these are what some people refer to as 'dual port heads' because the divider in the exhaust port goes all the way to the port surface)
others had inlet valves towards the centre.
-Some had dual carbs on a special manifold
-EA81T heads had injector bosses above the spark plug

Thats all i can think of at the moment

by this do you mean do they all rattle, have valve noise and will the run forever or until they drop a valve or throw a conrod in a fit of defiance

and truthfully that is a very broad question

well the answer is yes but the newer engines are different in the pistons rings and valve area due to that nasty unleaded petrol stuff

but if you want to pull and old one out and put a newer one in there are some cosmetic differences but not much else

you may need to drill the inlet manifold where it the bolts go to thru it to the block due to the heads being shaved or any different length ( I found that out just recently)
and on some motors the mounting points for the aircon and powersteering are not there or need to be drilled and tapped (as my friend found out)

TOONGA

earlier heads had smaller diameter valves of only a few mm, and their were 7mm and 8mm stem valves. Earlier cranks did not have that orange washer like seal between the flywheel.
Subaru in Australia do not support the hydraulic lifters parts as they were not in engines sold in Australia according to Subaru. Tried several avenues for hydraulic lifters over the years , but no sorry. Solids go harder anyway

And the newer the EA81, the more anti pollution gear hangs off it - but this is only on the inlet manifold

Cheers

Bennie

Also there is two different size intakes between the old and new. One is slightly larger and the other is. You need to take the carbie off to check but.