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Piston Compression Height Comparrisons


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#1 tdangelo

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Posted 11 January 2004 - 02:21 PM

I have been searching the Old Board as well as the New Board for valid information to back up the claims of compression increases by using different 92mm Subaru Pistons. Does anyone have the compression heights for the 1.1-1.6 Piston and the EA82 SPFI piston that some have claimed increase the compression ratio if installed in an EA81 engine. Without this information I find the claims, although they may be true, doubtful to me. I am seeking "hard number facts".

I am bulding an EA81, N/A engine, shared intake and shared exhaust engine. I am going to have larger intake and exhaust valves installed and I am going to use one of the New, not regrind, Ram Air camshafts and high performance spring kits. I will be running a single Holley/Weber carb.

I have access to a salvage yard that has an EA71 as well as a SPFI EA82 engine that are mine for the asking. So I am trying to use the best of all worlds without buying custom made stuff,

#2 Qman

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Posted 11 January 2004 - 02:51 PM

I don't have hard numbers for you, but...

I have physically seen the difference in the height of the EA81(1800) and EA71(1600) pistons. The difference is in the pin height in relation to the top of the piston. There is a difference but it is slight. It will increase chamber volume but I think the fact that most also deck the heads this may lose some of it too. I am running two different hi-per motors with different cam profiles. One is more torque and one is set up for higher RPM and horsepower. Most of you HP is going to come from your cam regardless of which pistons you use.

I will try to find the numbers for you in the FSM but it may be a while before I can post that info.




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