You guys got me interest, sooo I dug my 270" [5412 block-477 head]out & it has a piston with a raised hunp on the manifold side of the piston. EBAY item #120351779065 270"+.030 pistons have a concaved top. Will these pistons work with my head? Is my head such a poor design its not pratical anyway? I've done str8 buicks % 6 cyl chev. all my life & still learning, BUT this is the first GMC I've ever owned. Probally just thinking mild street engine, BUUUTTTT? THANK 1 OL REDNECK I.I.#113

The GMC 270/302 head came in 4 different designs. If you use a flattop piston with that head your compression will be about 5:1. Do a search on Google and you'll find all the info you need. The best head to use is the #983 with a custom piston.

My 321" GMC has Hudson rods (1.115 inches longer with a custom JE piston). The CR is 11.5:1.

Ron

Thanks RON . I've been fallowing all the posting by you about your engine plus many others on here . I will do the Google thing. Thanks 1 OL REDNECK I.I.#113

Basically there are 4 heads. Two, the early heads have "domed" chambers and use domed pistons. The earliest of these has small ports. The "H" head Has 1 3/4" intake ports. The next two heads use a flatter piston and similar but not the same D shaped chamber. The 302 head has the large 1 3/4 intake ports. For those who actually drive their Jimmys the small port heads are actually better on he street. These engines were used in trucks that hauled heavy loads all over the world. Any of them 228-302 will do well in a daily driver.