I am helping a friend rebuild a 350 engine for his K5 Blazer. He has a ZZ3 engine that scuffed a piston when a head cracked and let antifreeze into the bore. He also has a set of new Vortec heads so that is not an issue.

After cleaning the block and lightly honing it, all 8 cylinders measure 4.002 with no measurable taper or out of round. He would like to use the block as is and not bore it so my question is, Is there a standard bore piston that would work with this much extra clearance in a street application? Horsepower will be right around 350.

He would like to avoid the expense of forged pistons but would like something a little better than cast. I'm not an authority but I don't think hypereutectic pistons would like that much extra clearance. Anyone with real world experience have any suggestions?

Thanks

Bill

 

Piston OD to wall clearance is typically desired to be 0.002-0.003 for cast pistons and 0.006-0.007 for forged pistons. Since the stock bore is 4.000, I wouldn't worry much about having a 0.0020 overbore. If I remember correctly, the 350 from my Chevelle had around a 4.003-4.005 bore and I used the stock pistons with new rings. Just set your ring end gap per specs in the bores you have and you should be set.