Oval port BB heads???????

[Verne_Frantz]

OK, SO I am a dummy when it comes to this stuff, but based on something that showed up in the parts wanted section here, I'm just curious what the application differences were in a 206 and a 702 head. Why have TWO different oval port heads for 65-66????


Verne

[Dave Rifkin]

Would there be such a thing as an open chamber and a closed chamber oval port head?

[Xplantdad]

From what I remember...the later (read smog) big blocks had oval ports and open chambers

[WILMASBOYL78]

Check your Colvin book for the details..I believe the 206 casting was the first production BB oval port head released for the 65 model year...the 702 was the next version..don't have the book handy but I think thats the deal...probably some minor change to the casting..there were other heads after these ending with 290 heads in 1969-70...open chamber heads started in the 71 model year for regular production engines. By the way I have a matched set of 206's....

wilma

[John Brown]

Looked them up and it appears that only someone in engineering would know the difference. Both are oval port. The valves are the same, 2.06 and 1.72. Both have the spark plug shield bosses. The 206 head shows 97.167 cc's, the 702 head lists as having 98.427 cc's. Seems a waste to make a different head casting with the only difference being 1.26 cc's. The 206 head is listed for 65-66 396/325, the 702 is listed as 66 396/325&360 and 427/390.

Only The Shadow knows for sure.

[Xplantdad]

Like the 71 402...

[VintageMusclecar]

A brief gloss-over on oval port heads, FWIW;

All oval ports from `65 through `70 were of the closed chamber variety and all were factory equipped with 2.06 1.72 valves. There were minor variations in the combustion chambers over the years, with the later year heads having a relief cast in by the plug side of the chamber (if memory serves correct, the 290 and 215 heads have this relief). There were other minor differences in the castings over the years as well.

From 1971 through 1972, the oval port heads were of a semi-open chamber variety with a large relief cast into the chamber on the quench side by the exhaust valve. These heads actually perform pretty well on the street, although many enthusiasts tend to overlook them.

Starting in 1973, oval ports were cast with a true open-chamber design, i.e. the 049 and 781 heads, which are quite popular with countless performance enthusiasts and engine builders.

Hope that helps.
Eric

[Verne_Frantz]

Thanks for the education guys. I have a loner 702 that's not doing me any good except taking up room on my shelf.... Sure seems odd Chevy would have 2 castings that were so similar. I have to wonder if there was something else to it.