Forged or Cast?

Never say never but I don't think Jahns made anything but cast pistons until they changed there name to JE, Jahns Engineering.

If you've got plans that call for 13:1 pistons I'd like to hear more about what you're up to. The AMC 390 was a pretty good motor that is seldom mentioned. Had a 390 Javelin for 8 days in high school before it was totaled by a drunk driver trying to miss a stopped school bus but he hit us both.

FWIW, the AMC 360, 390 and 401 block was considered the strongest small block of this size in its day. They were built with 2 bolt mains but designed to allow for 4 bolt mains in the block and caps. The heads were considered anemic with the stock compression but came to life with higher compression pistons. It was a less expensive alternative to raise the compression than to change or alter the heads. In their day turbo's were almost unheard of and super chargers on the street weren't very common like they are today. At that time most people chased compression not boost.