When did they start to appear?

[Rob M.]

I am wondering when the 390462 heads started to show up on the "very late 1966 cars" and if anyone has a rough date?

The reason I ask is that my head came off this week and I am 99% that they had never been off the engine. They both are the 3890462 heads. The block cast date is D 7 6 and the pad read F0427. The heads are each dated D 22 6. The car's "birth" date is May 6.

Anyone with an earlier example of the 462 heads on a 66? Survey time?

[David L.]

Re: When did they start to appear?

Rob,

I have in my notes that I have seen a "3890462" cyl. head dated "C 1 6" (March 1, 1966).

Dave

[Duke W.]

Re: When did they start to appear?

The primary difference between 461 and 462 heads is the deletion of the small quench area on the spark plug side of the chamber, which increases the chamber volume by about 2 cc with the standard 1.94/1.50" valves. so the 462s are in the range of 62-63 cc vs. 60-61 for 461s.

The chamber relief on either type for the 2.02/1.60" valve set adds about 2 cc.

With the adoption of 462 heads for the full 1967 model year, Chevrolet reduced the advertised 327/300 CR to 10.25:1 from 10.5 with 461/461X heads, however, depending on block deck height the actual CR is typically up to 0.5 point below the advertised value.

This, along with the typical lazy centrifugal advance curve on 327/300s is why they usually operate detonation free on modern premium fuel which has slightly less (but not much) detonation resistance as sixties vintage leaded premiums, so most can handle either more compression or a more aggressive centrifugal spark advance curve.

Duke

[Peter J.]

Re: When did they start to appear?

Rob,
I don't remember the day of the 462 heads on my June 22nd car but they are June month casting dates.
Pete

[Peter L.]

Re: When did they start to appear?

Rob - OK, I found the heads for '66 S/N 25305 and they are both 3890462s. One is F 136 and the other is F 116; now all I have to do is find the block.
It reminds me of Tony Stein's footnote "Where did I put that part?" Just because it's BIGGER doesn't mean it will be any easier to find. Pete