I took apart a 70 sf block today,was wanting to save the pistons,but two of them are cracked. Is this a common problem with stock pistons? This engine came from old timers car that I can't imagine had much abuse. Hardly any ridge either,a couple nice size scratches though. I wouldn't think it was piston slap, maybe just old. What should I buy, the 7,000 rpm cast or the hypers,or are there some fairly inexspensive forged. I'm going to use my 76 block and it needs some cleaning up. .030 would take care of it. Do any of you have something I can buy to get 9.5 or so with my 70 heads? I'd take a good used set. Thanks Tom
Tom The last SF I took apart had 4 broken pistons with 70,000 miles. If you only plan on street cruisin I'd go with the cast pistons. Anything else I'd go forged and be done with it.
if you are not going to race it or some day want to build it up to 475+ h/p moter, i would just go stock or hypers as long as you keep the commpression at or below 9.5 to 1, with the hypers. but if you go with the notch forged, have your rods shot peened and APR bolts installed, then have it balanced. your bottom end would be built to handle up to about 550 h/p. it would cost you around another $600 to do that. just my 2 cents
Aren't hypereutectic pistons forged? When I did my engine (my pistons cracked right along the casting lines) I bought forged pistons, because the price difference was negligible and I never ever wanted a cracked piston again
Hypereutectic referrs to a type of casting which imparts an additional strength to the material. With a forged piston a stamping machine mechanically compresses the piston blank. This gives a stress harded enxterior, with a flexible core interior. This will prevent cracking, but allows for less expansion of the piston as it heats up, so you need a smaller, and more accurate clearance...something us Buick guys know NOTHING about :laugh:
The hypers have about the same expantion rate of cast iron, so you can run them tight in the bore, a forged piston expands at a different rate so you need to run them on the loose side, im not sure on the specs, but i know this is the main advantage of the hypers, but you must have your block set up for the hypers, or the could crack or explode.You could just hone a block and slap in forged or stock cast pistons and have no problems if they are in the proper specs.
Thanks Guys, Tom Rix made me an offer I couldn't refuse. I'll be using a set of JE lightweight .038 forged racing pistons.Thanks for all the input, Tom
