383...diff. year question...

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I edited my last post.... .090

Naw .090 would probably give you positive deck height. In regards to the deck height, have your block measured first. That way, you will know where the deck is before you have it milled. They are almost always too tall and crooked from the factory. What "I" would do is have it decked to the stock height. Tell the shop to square up the decks and make sure they are parallel to the crankshaft center line. Then, run the HP piston.
 
Mopar compression ratio's as advertised were fantasy land anyway. Blueprinted for nhra stock competition you could probably get advertised c.r. , but as delivered were probably at least a half point less than claimed. (The exceptions being the hemi and max wedge.....maybe).
 
How did Mopar keep the same comp. ratio in a 383 when changing from early closed chamber heads to later open chamber heads? Early heads are ~73.5 cc's, and later heads are ~79.5 cc's. What changed to maintain 10 to 1 compression?...rod length, piston pin height???
The early heads, 516 had a 84cc chamber. Although they are closed chamber it is still large. The 906 has more like 88cc. Only the 915 head was an honest 79cc. I think you have to take factory compression figures with a grain of salt. Im sure some were actually low 9s and some mid 9s and they advertised them the same.
 
Ok, I guess I don't understand. Theoretically, if the non-HP pistons, at 1.84 pin height, are .090 farther down the hole (~9.2:1) than the HP pistons at 1.92 pin height, would milling that .090 off the heads, or deck, get me back to HP compression (~10:1) ?
 
Theoretically, milling .090 off of the block would get that compression back. Then you will have to change pushrods, header alignment changes, bolt lineup with the intake will be way off, valve to piston clearance becomes much less, narrowing camshaft choice, vavletrain geometry changes. More, and worse, changes if you try to take it all off the heads.
If you want ten to one, buy ten to one pistons, dont try to make 8 1/2 pistons into something they arent.
 
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