VCCA Home Forums TECHNICAL - 1945 AND NEWER 1955-1957 Early SBC Power Pak Heads

I looked over a couple of dozen pre-1959 heads at a friend of mine's shop yesterday, hunting for a matched set of Power Pak heads having the same casting number, and also staggered valve cover bolt holes. With 25 or 30 pre-1959 heads to look through, I came up with about a dozen or so that were Power Pak, and of that number, only 4 or 5 that had staggered valve cover bolt holes. However, none of the 4 or 5 had the same casting number. I recall that the two heads that I liked best had casting numbers ending in 539 and 770, respectively.

Does anybody know if there are material differences in these casting numbers? I have removed mis-matched fuelie heads (like 461s and 462s from the same core engine before, so i know some people have run different numbers, but I wouldn't want to guess that the 539 and 770 Power Pak heads would be compatible --- probably too risky. Does anybody have opinions on the compatibility of these numbers? Anybody have a spare head with either casting number?

The staggered hole heads would be mid 1959 and before.The 1957 PP head casting number was 3731539.The 1958 was the 3748770.I don't think there was any difference between the two as the 539 was replaced by the 770 for parts replacement in 1958.The passenger car was not available with a power pac in 1959 but Corvettes used the 3755550 or 3760116 head in early 1959.
See no problem using the 539 and 770 heads on the same block :)

if the friend at the machine shop has any 3740997 heads, i'll trade ya a ton of 3731539's for a pair of the 997's.mike

Both are 59 cc heads, and both have the steam holes near the plug openings, so the combustion temps will be the same.
I see Mike likes those 55 cc heads, they can really wake up a dead motor
John

I believe that the 55 cc heads were used on cars with notched pistons.The 1957 power pac didn't have notched pistons and if over reved the valves would hit the pistons and fall into the cyl. and that was the end of the story.We replaced quite a few PP stick engines due to this.The 245 HP and up had notched pistons and 997 heads.Had the same 9.5 comp. ratio.All 1958 283's had notched pistons.

Thanks everyone for the input. Mike, my friend doesn't have a machine shop, but has just disassembled tons of Chevy motors over the years, so he very well may have some 997's. I'll have to look in his old schood bus where he has had them stored for about 20 years. Were the 997's also PP heads? Knowing that will help me check it out faster when I go there to look.

the 997's were a one year only chevy head and were found on the 220 hp, 245 hp, 250 hp and 270 hp corvettes as well as the 245 hp, 250 hp and 270 hp chevys in 57. one the ends on the heads, you'll find a vertically oriented narrow rectangle centered on the top of a fat horizontally oriented rectangle, the so called "single tower" head casting ID. The "double tower" heads, pn 3731762, were found on all 56 vettes. both 997 and 762 heads are extremely valuable-if you find any at your buddies, don't trade em for two tons of the PP heads. regards, mike