When I had the machine shop do my block I asked for a max of .040 over flat top pistons that would put my compression ratio to about 9.75:1. I didn't know much about piston selection then so I didn't care what they put in. Well by looking at them I know they are .040 over flat top cast aluminium CR 9.75:1 - 10:1.(CR was what I wanted)Now a year and a half later I don't want to pull the motor and tear it down anytime soon, but I am considering a NOS system but am not sure If I can without grenading the pistons. I read that with cast pistons you can go up to 125hp shot but after that forged is recommended. I think they where talking about forged and cast steel. So what about cast aluminum? Does anyone one know the limits on those WITHOUT taking ANY chance of grenading the motor. How much HP shot is possible? This is a 327 small journal crank with 23 degree aluminum heads a weiand stelth intake carter 600 cfm carb and this is a daily driver with an occasional trip to the track. I will use the nitrous only on the track (well maybe once in a while on the street) But it won't be used too much.

 

I am certain that the "cast" and "forged" terms were refering to aluminum as relates to piston material. I don't think pistons in modern gasoline engines are ever made of steel, at least none that I have ever seen. Maybe some of the other guys can help you on the reliability limits of cast pistons - I think your 125 HP limit sounds about right.