13:1 Compression Pistons in 340 Small Block
Mmmmm not really so much savings on the stroker. The big changes in modern pistons is in the crown underside shaping, the general crown thickness, and the areas around the pin bosses. That's where 80+% of the weight is. That applies for stroker and non-stroker pistons.
KB's for 340 for example are 588 grams vs the stock 719 grams.... so minus 130 grams just in the casting and shaping changes. Drop another 22 grams in the pins. (And those KB's for the 340 are a bit thicker in the crown to push the dome up.) Those old forged domes ain't gonna be any lighter than stockers with the older designs.
The 360 stock stroke KB's are 510 gr vs stock 576 gr stock; drops to 478 gr for an equivalent KB stroker. Not all that different a change versus than the stock stroke ones; the general casting design makes a bigger difference.
You can see these same general casting/forging design changes for lighter weight show up in the 90's in production pistons in GM and Ford engines at the least.
BTW, not the place to do this, but at some time, I'd like to discuss this idea of power difference based on the head material.... This has showed up again recently.
I agree with your comments about the shaping under the crown.
But I also notice in your 2 examples with the Kb Pistons for both the 340 and 360 that assuming the same deck height as soon as you posted the 360 numbers for the kb and the stock weights, both numbers on the 360 were much lighter. A small block has a relatively tall deck height for the size of the engine.
With a short stroke and a 6.123 rod, and the pin location where it is, makes for a fairly tall piston.
When comparing the weights of Pistons you can get into a whole bunch of engineering that is way over my head, but a 4.00 inch stroker piston has its pin moved up higher. Because of this the Pistons are also shorter which also makes them lighter. I believe they can make them shorter because the pin is moved up and the shorter skirt will still remain stable in the bore.
Although 152 grams may not seem like much of a difference in weight, your rod bolts will say otherwise as they try to yank that piston down after the exhaust stroke at 7,000 rpm lol.
The loss of power with an aluminum head is well documented.
The work around is to build the motor with 1 number higher compression. Almost all all out race motors that are using aluminum heads, build with a ratio of 14:1, with cast iron it is 13:1, everything else being equal.
