unless you want to spend big bucks on forged slugs you will have to try oem replacements. as for the head the sss 38cc is too much you will need something with a bigger chamber say 41cc or biggerthat will lower your comp some keep in mind even the u67 open chamber head is usable for boosted applications.

here are rough comp #s with stock L-20 dished pistons

41cc head a87 type 9.0:1
45cc head u67 type 8.5:1
38cc sss head 10.8:1

if you use a reduced deck piston you will not cause detonation on the contrary it will help by reducing the compression further

U67 head turbozx pistons 8.0:1
u67 head Z20 pistons 6.5:1
a87 head Z20 pistons 7.5:1
sss head Z20 pistons 8.0:1

I hope this is usefull personally I'd go with the last combo, it will be the most resistant to detonation due to the larger squish area of the head and the reasonable compression. you should be able to run rediculous boost with this setup. I would also recomend looking into a bigger carb and water injection if you plan on staying with a draw thru setup.

so the best combo for what we are up to is a sss with 81-83 z28 pistons with a dish? if i did my research right there are two diffrent pistons one flat and one dished. go water injected (with what size jet?)and most of all get rid of the intercooler.what carb setup would be best? you have to remember we are dealing with steep hills and rough conditions so it has to fairly easy to tune for such thanks for all the replies again

if you feel like fabricating go with a holley 4bbl the increase in size will also increase the air flow thru the turbo and they seem to be stable in rough conditions as for the water injection start asking around the draw thru turbo group most of thos guys have had turbocharged cars longer than I've been breathing