If a STD 350 block is 4 inch bore, what size is the piston? It can't be 4 inches as I am sure that must be some side clearance built in. I heard that there is a difference in cast, forged and hyper pistons too... so... what would a std size piston diameter be for a 4 inch bore 350 for cast, forged and hyper? thanks..

The clearance is taken off the piston at the factory.

So a 4.000" bore takes say, a 3.995" piston if it is a forged piston that needs .005" expansion allowance clearance. (Which some of the older ones did!!)..

AND you have to read the manufacturer's spec. sheet to see where to measure correctly the piston to make sure it is measured correctly to the bore!! B/c some measure 90 degrees from the pin ends, others measure other places like down in the middle of the skirt??? It just depends sorta deal is all..

pdq67

[This message has been edited by pdq67 (edited January 24, 2005).]

So it's not as easy as it sounds. Buying a block that is already 30 over does not mean you can just buy a set of 30-over pistons from Jegs or Sumit and have them fit correctly....uuuggghhhh.

Thanks for the info.

I did exactly what you want to do, I had the block bored and got the pistons after. I ran into no problems at all.

If you are not racing the thing, you can almost always buy a set of .030" pistons and they will be pretty close to what you need. This is assuming that your block was bored and finish honed to 4.030" and not just honed to clean it up, etc.

Yep... thats what I have. I checked the block and it is right on 4.030 with the cylinders honed. I was going to buy a set of KB 30 over pistons but just wanted to make sure that I didn't need to do any more work to the block. Looks like I might be ok. Thanks..