I'm thinking they either exceeded practical total timing limits which I think is around 34, except for Lt1/4s where you can get away with a good bit more, or failed to properly fit (particularly) the top rings. I spent two evenings fitting mine in their respective holes perfectly squared at a specified depth. In my case it was .026" top and .018" for the second ring. I was breaking it in and seating the rings with repeated hard runs to 5,000+ within the first half hour of it's life and have done extended hard runs with it since. Hardly a day goes by that it doesn't see redline. No problems in 4,000 miles and counting, time will tell I guess.

 

Wait a minute, I have an '85 GM Shop Manual and it says that the pistons are cast Al alloy with two compression rings and one oil ring....??

BTW, the identical description is also in my '88 GM Shop Manual.

 

cant always believe what u read jim, u know that............

 

True...but where...one would hope that the General is on the money...

 

My 1984 Factory Service Manual says cast, too. But wait until you see them. They aren't. Trust me on this.

RACE ON!!!

 

Looks like an "oops" twice for the General; thanks for the heads up.

 

My service manual also says to use a T-45 Torx bit on the rear wheel bearing bolts. Make that, 3. I'll bet there are more, too.

RACE ON!!!

 

Ya' think? My '95 manual also had me take half of the rear end of my car apart to change the antenna. Now that I know how to do it, I can swap one in half an hour.

 

I was going to use Wiseco "Pro Tru" forged pistons on my 383 project engine. Anyone have any comments about Wiseco pistons? I don't see them mentioned very often here on the Forum.

 

Wiseco is a very respected name in pistons. Many serious racers use them.

 

hi guys, for some clarity on the c4 pistons, from the book byMike Antonick, (same guy who wrote the corvette black books)COR-VETTE SPECS 1984-1996: both 84 and 85 had forged pistons, 86 and onwards had cast aluminium. Great book, ISBN 3382534515. Replacing one of them if its been damaged, you really have to match the piston for weight and construction which means replacing with an identical piston, or put a new full set in. On the subject of how good are the originals, well here goes it. I have run an 85 with a single and also twin turbos with re-ringed standard 85 forged pistons to hell and back and never broken anything. I also currently run an 84, with re-ringed original forged pistons, with a centrifugal supercharger and have had no problems with the pistons from 5 to 18 lbs boost. Not using an intercooler, i built my own water injection and never have detonation problems or the miriad of problems we read about online with water injection. Yes just plain tap water with no additive. (hi pressure pump triggered by boost level switch, simple and effective. it only sprays when on boost).

 

Thanks for clarifying an 11 year old question.

 

I really like my forged pistons, a person I met at a meet had a nitrous set up on
his 85 stock and been running it without any problems. I am not running nitrous but I feel confident with trws. Like the OP said mabey left over from 83 but too expensive for 86 late and on who knows.