I have a set of domed pistons that a coworker gave to me. They are hypereutectic aluminum. The problem with these is there were only 7 when he got them from a friend of his. The guy that he got them from used to be great friends with several people from various nascar pit crews, so it is possible that these came from one of the teams, but I really don't know for sure. They are GM direct with the dome offset center with 1 valve relief. He said the pistons were discontinued so he couldn't get a replacement. 2 are still in the original boxes with the part number 3969983. There is also GR. 0.629 stamped on the tag and S6 stamped below that in large print below the tag on the box and on the pistons. Can anyone tell me anything about these pistons? Possibly the compression ratio or what I can do to replace the one I am missing if not? They appear to be 4.060" pistons. Right about 4 1/16". If I can replace the one missing, they would be a nice set to use later. They have never been installed, just left on a shelf for years and I would hate to put them to rest never having been used. I'll post pics of everything tomorrow.

 

Well if they have been discontinued... I can't see you finding a new one one unless someone is selling one on ebay or something. All I can think of is having one custom made, but I assume this would be expensive, and I don't know if it would even be possible. I would just keep your eyes open on the net, there's a chance one might show up somewhere. You could also probably find info about them somewhere on the net.

Personally I wouldn't use domed pistons. I have read about how bad they are for flame travel... I'll stick to flat tops, unless it's a full race only engine.

 

pistons from most, if not all, makers are weight matched untill they have enough to make a 8 piece set. for you to find a equall weight piston you'd have to weigh pistons. think i'd just buy a new set.

 

I dunno. I know a guy that casts his own stuff and then machines it to whatever specifications he needs. He'll do it for almost any part for $100 shipped, which is ALOT better than $650-$800 that a decent set of domed pistons cost. Then again, I am not sure about hypereutectic aluminum. They may be a bit cheaper than that. That's the cost for forged pistons. As far as the pistons mainly being for a race only engine, that was really the point. I had planned to buy stuff one thing at a time and make a strict drag race only car. I had hoped for pro street mod, but with everything I had planned on, I really doubt I would be able to stay in that class. I'll probably be looking at around 1200-1500 rwhp at first. Then maybe stepping up to a 427 and getting much faster, but the only major problem with that is with a big block, you have no control. If something goes wrong, you have a long distance between you and where you will stop at.....IF you are lucky. Thanks for the info. If anyone has ever had a set of these, let me know. I'll get pics up either this afternoon or tonight. I work second shift.