Subaru Compression Ratios - and WHAT IS EA-71?

[EDMO 1078]

I CANT FIND the posts where we were talking about using EA-71 pistons in an EA-81 to raise the compression.  So, What is the 71?  Is that the 1600cc, with same bore but shorter stroke - where the 81 is about 1800cc?

I looked in my Chilton Subaru book tonight and here is what I found on the EA-81, but no other piston dimensions were given - just clearances.

1980-84

Turbo charged = 7.7 compression ratio, 95 hp, at 4800 rpm

2 barrel carb = 8.7 ratio, 72-73 hp at 4800 rpm

1985-87

2 barrel carb = 9.5 ratio, 82 hp at 4866 rpm

MPFI            = 9.0 ratio, 94 hp at 5200 rpm

SPFI            = 9.5 ratio, 90 hp at 5600 rpm

Turbo           = 7.7 ratio, 111 hp at 4800 rpm

     Now, the question is:  Other than the Turbo, did they change pistons to change compression, or did they do something else.  I don't have a clue!

I was told that milling the heads .040 would raise the compression from 8.7 up to 9.1 on the early models. 

And that the automatic trans had bigger valves and hydraulic lifters instead of solid - and that the cams will not interchange - the hydraulic cam has an extra groove around it for identity - and no adjustment on rockers.

but you could have the heads machined to take the bigger valves with the solid lifters.

NOTE:  These hp ratings are for the original engines in cars - for planes, the hp is rated higher.

Hope this info is usefull to someone.

EDMO

Edited 10 Mar 2014 by Ed In Missouri

[IFMT 36]

Thanks for the interest Ed. The ea71 is the 1600cc. The only dimension I can find through internet part searching is the bore at 92 mm. Same as ea81. 1600cc has shorter stroke. I know the simple answer is to take the .040 off the heads but then I have to make another manifold. I saw that RAM sells manifold adapters. I want to keep my 2 barrel carb set up as I already have it as it works. I do have carb heat but with the stock manifold I can't say I've ever needed it. Another thing with the carb heat and the stock manifold is that I can't tell any difference with it on or off. Not like an aviation engine where the RPM drops with carb heat applied. Might help the HP with dense cold air. What is the size of the 'bigger' valves. The engine I want to rebuild will need a complete going through. I see it was opened up before and whoever did this was sloppy. Pistons switched left and right and wrong washers under nuts on heads. I'm a licensed heady duty mechanic. I know that doesn't mean much but I do understand attention to detail and building this things absolutely right. I'm going to order a set of the 71 pistons and try it. Where is the extra groove on the cam. This engine is hydraulic lifter.  Cheers.

[EDMO 1078]

I cant tell you right now what is needed for the manifold to fit after milling the heads - I know that has been done to mine, but the guy who did it is dead.  I do have some papers he sent me a long time ago - somewhere I have some old issues of CONTACT magazine where RFI was making the conversions and telling how to do it.

If I can find and info on the manifolds I will post it or PM it to you.

One suggestion I might have for you is to contact Subaru Service Dept. and see if they will tell you if any difference in the 1800 pistons in the years that I have posted.

You know that when you increase the compression ratio from 8.7 to over 9.0, you will probably have to use a mid-grade or higher octane gas.

I will look for the valve info, but Subaru might give you that info.  If you have hydraulic lifters, you should have the larger valves too.

Are you going to have the cam reground to raise the torque from 2400 rpm up to about 3600 like Stratus does?

EdMO

Added:  If there are washers under the rocker arm posts, then that is an indication that the heads have already been milled.

Edited 10 Mar 2014 by Ed In Missouri