Hi folks. Maybe I can add my own 2.5 cents (inflation) worth. The following might not be earth shattering, but it might shed a kernel of info on the subject. As many of you know, in order to compete in NHRA Stock (and Super Stock) classes, the specific car as well as specific engine combinations have to be presented to the NHRA for acceptance by the respective factories. From the vintage Chevy perspective, that job fell in the hands of Product Promotion (Vince Piggins office). Now it's no secret certain liberties were taken (then and now) by the Detroit manufacturers so that their own production cars would be advantageously classified and have the best possible hardware for the class. It was called "being competitive". Plenty of interesting combinations (and equally interesting factory horsepower ratings) came out of this. 335 (rated) horsepower 428 Cobra Jets, LS6-powered 1971 Chevelles, any number of goofy Max Wedge cars and so on. They all more or less met the letter of the rules, at least when they were presented to the NHRA.

But in spite of these liberties - and some were considerable, I can't find a factory produced aluminum head 1970 396 (402) combination within the NHRA classification guide, especially one with 074 heads. As a note, the paperwork for the 1970 Chevrolet model year was originally issued on 23 March 1970, and revised a couple of times in 1970, so there would have been plenty of opportunity to include "rare" combinations. Certainly, the 401 casting (recent) replacement aluminum heads are listed, but they don't enter our discussion.

So I guess the point is, even if Chevy made something as rare as none of none, it was sometimes included in the NHRA Classification Guide. But the topic one of one combination is not.

I agree with many of you. The real key is the use of open chamber heads on this particular engine. As far as using 074 open chamber heads on a closed chamber 396, I sincerely doubt Chevy would have done that, even on a bad day. I've even done the open chamber head swap on a closed chamber piston engine decades ago. As others have pointed out those parts didn't really like each other. Amongst other things, it required the thickest head gasket I could find. My math shows, even in a perfect world with incredibly tight blueprint tolerances a 10:1 compression ratio would pretty much the most one could expect (and in the real world, I suspect a C/R of 9.5:1 or less would have been more realistic). It would have been a dog to drive I'm sure, at least in comparison to cars equipped with more standard 396-375 engines.

On the other hand, it'd be a bad ass day two car with an L88 or LS7 shortblock underneath those 074 heads.

Wayne Scraba