heres a good read

Old TRW piston clearance. - Don Terrill’s Speed-Talk

heres another idea, email the seller and see if the specs are in the boxes.

NOS TRW L2256 Forged Pistons 350 Std Bore Chevelle Camaro LT-1 Nova SS L82 | eBay

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Use the current spec for a 2618 forging, that is the old time material that undergoes more thermal expansion that the more modern almost hypereutectic 4032 forgings.

Bogie

 

A bit off topic but when something pops up in my head , at my age , if I don't act on it I'll forget about it . the standard answer to 4 valve reliefs is " so they can be used in either side of the block , great , why does the piston have "front" stamped on the crown ??

 

The piston pin is offset to the thrust side to reduce skirt slap. The thrust side is the same direction for either bank so the piston in this regard is directional. The valve reliefs are for the valves which in terms of inclination to the bore center reverse side to side. By using two pair of valve reliefs the same piston can be used on either bank. So this saves the cost of two machine setups to cut valve reliefs only where needed. You should see when browsing piston catalogs there are models with only two valve reliefs and typically they are more expensive because now instead of one piston fitting the left and right banks instead these pistons with only one pair of reliefs are side dedicated to as either the left or the right so you make 4 pistons on a set up instead of 8.

In the somewhat abbreviated words of John Glenn on reaching the moon; “all of this from the low bidder”.

Bogie

 

I can't tell you what year it was and perhaps might be off by one or two, but those pistons I used them back in the early 2000's and I do believe they have a 6cc dish from the valve reliefs and they are a 1.560 compression height. Now that was a long time ago and the pistons when I bought them was under the Speed Pro name and was sold all over the place way back when. They also have a 5/64 5/64 3/16 ring size.

I ran them on a 383 stroker with 5.565 rods and 3.750 crank and then after rebuilding the engine with a roller setup I went back to a 350 and reused them pistons. It was with Dart Iron eagle heads and pretty decent sized cam. They are good pistons for being forged and are the 4032 material which is stronger and better then a Hyper piston but not as strong as the 2618 variety but if its just for a everyday cruiser then they are more then good enough. I use a DSS brand 4032 forged flat top in my current build and would never think twice about using those TRW.

Only downside is I don't think they take C clips or spiral locks. I don't know what all they had back then.

 

the 2256 is heavy, maybe even the same weight as the stock cast piston

 

Typical NA street use will be .003-.004
Power adders will be .001-.002 bigger