Hulk0202

Can the pistons from the higher compression pre 72? 350 be used in a late model (81) block. Is there a lack of valve reliefs in the pistons, is that what gives the higher compression. Any clearification would be greatly appreciated. Thanks

Vader

Hulk,

Presuming the early SBC was stock dimensions (no special deck height), the pistons should work. The rod length should still be 5.70", and the pin location should be the same.

You'll have to watch the valve interference very closely. Piston top valve reliefs are usually responsible for about 6CCs, but can be necessary for safe clearance. That volume can make a difference in compression ratios. On a 76CC chambered head, all else being equal, the valve reliefs lower the compression from 9.2:1 to 8.7:1. Many aftermarket pistons will have only two reliefs, and some sets have none or only have one relief for the exhaust valve.

Of course, the camshaft profile and valve train will have a big effect on piston interference. Standard precautions are advised. Get out the Play Doh.

Another thing you should check closely is skirt interference. I've seen some older engines with precious little space between the skirts and counterweights. Mixing a newer crank with the older pistons could present a problem here, but it is certainly worth a trial fit. Factory pistons shouldn't have a problem with this.

Hulk0202

Thank you Vader. Thanks for all the info. you've given me past and present. Your a great asset to this board.

RB83L69

The early pistons are flat-tops with valve reliefs, the later ones are dished. VRs are somewhere around 4-6cc, the dish they used is around 18cc IIRC.

If you are running a cam with less than .600 lift and any kind of stock head castings, there's very little chance of a clearance problem.

I have never seen a skirt hit a crank in any stock-configuration small block; I suppose it's possible, that is to say I haven't seen every piston and every crank there is, but if you look them up in the books, pistons for 350s are not year-model specific, except for replacement applications that call for particular dish/dome/flat configurations. So I would not worry about it.

A 81 block is not "late model", except that it will (probably) have a RH dipstick, which is not a very big difference in the casting.

Look up pistons on Summit's page or at your local parts store in the paper catalog, you can get a very good picture of interchange possibilities from that. For things where the book says something like "350 67-92 all" you can be pretty sure you won't have a problem.