383 compression

[Don Dulmage <big-d@xxxxxxxxxxxx>]

The low compresion pistons are different and lower in the bore.  or have a lower compression height if you want the technical term. Now it gets dirty. too lazy to build a proper piston for both engines  piston maunfactures fudged the specs for both motors and produced a so called 9 to 1 replacement. piston. Ever seen a 383 redone and it seemed to be ok but lacking just that something? Well that is why. Even Momma mopars are fudged them. 
the only real 10 to 1 pistons are the TRW forged replacement pistons. I have been unable here to find any others. TRW number is L2315F and they like the original magnms were only "close to 10 to 1 if the heads were in spec. (79.5 to 80 cc. ) Most heads are acually 86 to 91 ccs so even with everything going your way you could still wind up with 9 to 1 or less even with the good pistons if you didnt take care of the head thing. Add to that  the extra 020" for felpros over the original steel shim gasket and your back to an 8.65 or something to 1 engine with all 10 to 1 parts. if you have the wrong pistons to start with for example it is possible that even 8 to 1 would be unreachable. 
This is BTW why cc the heads is so important. it doesnt have to be a "super critical gotta pass tech" job but you need to know how much extra meat you heads have on them above factory specs.  I use and have for years used a large cattle siringe for checking them .(In another life (during my career Sabatical) i was a cattle trucker and feedlot operater "Dolmetsch Beef Farm")  TSC should have that in stock. You can get a 50cc or 50 ml siringe and you will have to fill it twice (or get two. ) a dab of dishwashing soap in your water will keep it from forming a surface tension curve. Then just screw in a spark plug and level the head and gently squeeze away . Keeping track. Not fancy but very practical.  The few minutes spent here and the few dollars spent correcting this alone will yield mountains of burnt rubber and tire smoke if you are so inclined. 
Don

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