Got the 390 torn down and the block is std. The pistons out of the 360 are slipper skirt and have a 304NP marked on them as well as the .030 on the top of the piston denoting oversized status. These look like aftermarket cast pistons. They also look identical to the 390 pistons (marked 410) other than for some cosmetic appearance stuff. . There was a pretty good ridge on the cyl. on the 390 block so it will probably need to be bored to whatever. ? is this. Can I use the 360 pistons (+ .030) in the 390, with the 390 rods (C7AE-B units). I am assuming the wrist pins are the same? What should I check on the pistons to insure integrity? How much differance in sizing is allowed? Also when the block goes out to be hot tanked, machined etc., I am assuming I should send the pistons with it. Is there anything to be gained from match boring the cylinder bores to each piston, with the proper clearances of course. Lastly, what type of ring is best, chrome, moly, etc. Pricing is only an issue to the extent that I don't want to spend it if I am not gaining anything in reliability and/or peformance. I am one who holds to the statement that the cost is high only if it isn't done right. sorry this is so long but you guys are super and the most knowledgable folks I have conversed with on here or elsewhere.

 

Got "THE BOOK" by Steve Christ finally. answered my own question. 360 piston is too tall from wrist pin to piston top.

 

Az, why are thinking the 360 pistons are too tall ? The 360 pistons i have seen and or read about are 1.76 tall, or somewhere thereabouts. 390 pistons, the ones from cars at least, are the same height. One rarely sees a real 360 piston anymore, they would be the full skirted jobs. Most 360s were assembled with pistons that were originally intended for the 390 4V engine, and have flat tops with 4 vavle reliefs. DF, from his Dad's house

 

What threw me was that the distance from the wrist pin to the top is different between the two pistons. The 360 IS 1.776 and the 390 unit (marked 410) is 1.68. I guess you would call that the compression height. The 360 piston (aftermarket, .030 over, marked 304N) is about .096 "taller" referenced to the wrist pin center. I was worried but then my BOOK was delivered and gave me some info I needed to double check. From the Big Block Book using the stuff on pg.38 and 39, doing the math I will get a Deck Clearance of about .032. Actual measurements I got left a Deck Clearance of .030 so I feel pretty comfortable with the numbers so far. Normal deck clearance is listed as .112 so if my thinking is right I will see a rise in the compression ratio. Is this correct and is there anyway to quantify this "new" ratio? Also I am assuming the 390 rods will fit the 360 pistons as far as the wrist pins go?

Does this check out cause I have been wrong before, lol