I have a newly built mild 383 in my 93 TBI PU.  It has stock heads and a mild cam with supposed 9:1 pistons and I can't get it to stop pinging.  I gave up trying to fix and took to a performance shop - he checked everything out and said compression is 205 psi.  

Thats way too much for the stock heads yes?  He thinks the builder put in the wrong pistons.  Does anyone know what psi a mild stroker should be at?  185-190?

thanks  

Those factory heads have small chambers, you can't just assume they are the same old open chamber 350 heads from the '70's...

Even a flat top in a 383 can make nearly 11:1 compression with 64cc chambers and depending on if the block was decked or not. Couple that with a small cam and I can see why your cranking compression is too high.  

Were these your original heads? If not, get a casting number from the heads and look them up to see what they are! As stated...if small 64 cc chambers are used, you may need to do a head swap to correct the compression ratio and drop the cranking psi. I would not think you want more than 180 with small cam. A bigger overlap cam bleeds off low rpm pressure so sometimes can get away with higher compression.