Raising compression on an EA81...best methods?

[Brettm57]

From my research in the service manuals, I see two relatively low-cost possibilities. One would be to mill the heads and/or deck the block. The other would be to use 1600 heads on an 1800. I seem to remember reading on here somewhere that the valves are smaller in the 1600 heads. Can anyone verify that for me? And will 1600 heads bolt up to an 1800 block? Or, if the 1800 does have bigger valves, can they be installed in the 1600 heads? If that won't work, then how much can be milled from either the 1800 heads and the block deck and still maintain some sort of reliability? I have access to the machine tools necessary to do anything listed above, making machining cheap (Free!). Thanks in advance for your help.

[Ross]

You probably mean 1600 pistons, not heads. You can also pistons from an ea82, the SPFI ones will give you a compression ratio of 9.5:1.

 

You are limited in planing the heads by the intake manifold. Unless you somehow shorten it, or fabricate a new one, it wont fit after planing the heads much.

[Brettm57]

Not trying to be rude here, but no I was thinking 1600 heads. I'm guessing that the chamber in the 1600 heads must be smaller than on the 1800 heads. This pretty much holds true on domestic (Chevy, Ford, etc.) engines. But I don't know for sure about the Sube engines, I've never seen either one apart. Can you tell me the difference between EA-81 and EA-82 pistons that lets them increase compression? Thanks for your help.

[Ross]

The tops of some (SPFI and MPFI N/A) ea82 pistons are higher, thus raising the compression ratio.

[Jerry DeMoss]

I personally don't have experience with the ea71 heads but I have heard of many people running the ea71 pistons and then you can also mill the heads and take .040'' off of them.I am guessing that the ea71 pistons and milling the heads down will get you a little above 10:1 cr.I personally would like a little more....But I may be weird.

[Brettm57]

The guy at Ram Performance tells me that there is no compression gain using EA-71 pistons in an EA-81. I was pretty impressed with our phone conversation, I think he knows what he's talking about. But the EA-82 pistons sounds like something worth looking into. I've done several searches looking for the info on EA-71 heads, but haven't turned up anything. I remember reading something about these heads having a smaller chamber, but the ports and valves were smaller also, cancelling out any gain from the higher compression. Oh well, I'll keep looking.

[NoahDL88]

The Ram Engines guys know what there doing

 

 

Using 1600 Heads on a 1800 dosn't sound like a good idea, any gain you'd get from the higher compression would be off set by the smaller valves I don't know if they even fit, and if they did i believe they use a different intake, which is smaller than the 1800.

 

My reccomendation, ie, what i did with mine.

 

Milled heads .030, any more and the intake dosn't fit

EA-82 pistons

Oversized valves with 3 angle valve job

Port and polished the heads

Delta Cam

Re curved Distributor

Weber 32/36 carb, but in retrospect the SPFI would have worked better

[Brettm57]

Noah, you wouldn't happen to have any pictures comparing the EA-82 and EA-81 pistons, would you? And, how oversize did you go on the valves and did you replace the seats? And, if you did mill the heads more, could you slot the bolt holes and grind the ports in the manifold to make them match up to the heads? I'm at a real disadvantage here, I've never seen one of these engines torn apart. Thanks for your help.

[subarunuts]

I've compared the 1600 pistons, and the wrist pin is slightly lower, giving an increase in compression over the entire face of the piston. 1600 heads will not fit an 1800 block, and the valve sizes are considerably smaller - in fact even the early 1800 intake valves were smaller till '82 when the intake valve size was increased by 2mm. Remember that while the RAM performance people do know a lot, they also make their own pistons so why would they care about EA71 parts, or even bother checking. The difference is slight, but definately exists - I measured the difference at about .008 or so. Without changing the cam tho, the EA81 has difficulty running anything but premium gas with even mild increases in compression. Decking the block or going more than .030 on the heads will result in the need for custom intake manifold - not impossible, but with coolant running in it, it's not a small job either.