Basic internals ??

[Scoobywagon]

I got to wondering about the interchangability of parts between the EA71 and the EA81. I'm under the impression that EA71 pistons can be transplanted into an EA81, implying that at least the top end of the con-rods in both engines is the same. If this is true, then it stands to reason that the connecting rods ARE the same with, perhaps, differences in length. That, in turn, implies that the cranks SHOULD interchange. Is this the case?

 

I was thinking of ways to get more go-fast out of an EA81 and it ocurred to me that a shorter stroke and lighter rotating assembly would do wonders. Now, as far as I know, both engines have the same bore, so the difference in displacement must lie in stroke. So, I'm thinking a lightened and balanced EA71 crank (knifedged, maybe?) with EA71 Conrods and EA81 pistons in an EA81T block, Extrude Honed Intake and heads, and a somewhat beefier turbo. Add in enhanced engine management and some good ignition control and I think we've got a winner. Any thoughts?

[NorthWet]

So, what are you after? A smaller displacement engine that won't rev any faster than the EA81? The EA81 already has a pretty short stroke, and the crank and rods (with attentive prep) should be good for 9K rpm... more than you are likely to get out of the valve gear without significant work.

 

* Edit - I wrote this in early morning after work. Reread it after some sleep and it sounds too argumentative/attacking. Definitely NOT what I meant, Charlie. The EA81 already has a pretty good setup for high-rev'ing, though I haven't looked closely at crank oiling. Need lighter valve retainers, dual/triple valve springs... ought to scream! Oh, and solid lifters, guy. - end edit *

[idosubaru]

according to this thread they are interchangeable:

 

http://www.ultimatesubaru.org/forum/showthread.php?t=22848&highlight=ER27+pistons

 

check out like the 2nd or 3rd post, someone mentions it.