C2 Head Question

[Frank C.]

I have a april built 1966 Coupe with the L79. I am rebuilding the engine.

The engine assembly date: April 12, 1966

The heads on the engine are:

Drivers side: 3782461 dated A256 = Jan 25, 1966
Pass side: 3890462 dated C 8 6 = March 8, 1966


My question, would typical factory productin have two different casting numbers and the dates 3 months apart?

IMG_1536.jpgIMG_1522.jpgIMG_1525.jpg

[Frank C.]

Re: C2 Head Question

I mis posted one picture above. here is the other date code.

IMG_1524.jpg

[Jim D.]

Re: C2 Head Question

Typical? Probably not. Possible? Probably. My 65 has 461's both dated the same day (4 days after the engine casting date and 4 days before the assembly date).

[Gene M.]

Re: C2 Head Question

Frank, typical that the 462 is a 67 Corvette model year.

[Joe L.]

Re: C2 Head Question

I have a april built 1966 Coupe with the L79. I am rebuilding the engine.

The engine assembly date: April 12, 1966

The heads on the engine are:

Drivers side: 3782461 dated A256 = Jan 25, 1966
Pass side: 3890462 dated C 8 6 = March 8, 1966


My question, would typical factory productin have two different casting numbers and the dates 3 months apart?

[ATTACH=CONFIG]40312[/ATTACH][ATTACH=CONFIG]40313[/ATTACH][ATTACH=CONFIG]40314[/ATTACH]

Frank------


I think it's very possible the heads are original to the car. Your engine was manufactured in the general period of the change-over of the two head casting numbers. I would say that it's unusual for an engine to have 2 casting numbers but within the range of possibility in your particular case.

The 3782461 and 3890462 heads are functionally interchangeable so there's no reason the factory would not have been able to use one of each on the same engine.

[Frank C.]

Re: C2 Head Question

Joe and Jim,

Thanks for the replies. I read in the JG 462 heads are possible on late cars. It would be interesting to know when that started. I have a very original car. In response to Jim's post, most of the cast and numbered parts for my car are dated in the March 66 timeframe, so that is why I asked the question. I will have the shop check the heads for faults. As long as they check out, I intend to reinstall as I found them.

Frank

[Duke W.]

Re: C2 Head Question

Given the date codes, it's possible the heads are original, but, if so, it was certainly poor engineering/manufacturing practice.

The 462 heads eliminated the small quench zone on the spark plug side of the head. This increased chamber volume by about 2 cc, which means, all other things equal the 462 side will have about 0.3 less compression.

If you are doing a precison rebuild I recommend you do something about this. You could get another head to have a match, and you can also compensate for the difference in side to side compression by using a thicker head gasket on the 461 side, assuming both sides have about the same deck clearance. If the deck clearances are different side to side mounting the 461 on the high side will offset to some degree the larger chamber on the low side.

I suggest you dig out your Fall 2009 Corvette Restorer and read "Compression Ratio Explained". If you are doing your own disassembly/assembly you are in a good position to manage the final CR.

The head mating surface should have broachmarks similar to the block. If either of them shows radial tooling marks typical of a machine shop cut, the story will be more complicated.

Duke

[Loren L.]

Re: C2 Head Question

Could I suggest the "possibility" that your 461 head is from Tonawanda?

[Patrick B.]

Re: C2 Head Question

Could I suggest the "possibility" that your 461 head is from Tonawanda?

Wouldn't a Tonawanda head use 66 instead of 6 in the casting date?

[Joe L.]

Re: C2 Head Question

Given the date codes, it's possible the heads are original, but, if so, it was certainly poor engineering/manufacturing practice.

The 462 heads eliminated the small quench zone on the spark plug side of the head. This increased chamber volume by about 2 cc, which means, all other things equal the 462 side will have about 0.3 less compression.

If you are doing a precison rebuild I recommend you do something about this. You could get another head to have a match, and you can also compensate for the difference in side to side compression by using a thicker head gasket on the 461 side, assuming both sides have about the same deck clearance. If the deck clearances are different side to side mounting the 461 on the high side will offset to some degree the larger chamber on the low side.

I suggest you dig out your Fall 2009 Corvette Restorer and read "Compression Ratio Explained". If you are doing your own disassembly/assembly you are in a good position to manage the final CR.

The head mating surface should have broachmarks similar to the block. If either of them shows radial tooling marks typical of a machine shop cut, the story will be more complicated.

Duke

Duke-----


GM specs list the 3782461 and the 1966 version of the 3890462 as having the same combustion chamber volume at 62.076 cc for each. The 1967 version had a slightly larger volume at 63.305 cc.

The cylinder head used for 1966 L-79 was GM PART NUMBER 3853608. The same cylinder head PART NUMBER was used for 1967 L-79. As far as I can tell, the GM PART NUMBER 3853608 cylinder head was manufactured from both the 3782461 and the 3890462 castings. Since the part number was the same, GM would have considered the cylinder heads the same regardless of which casting they were manufactured from.

[Duke W.]

Re: C2 Head Question

I've never seen any GM specs for head chamber volume. Most AMA specs list TOTAL combustion chamber volume.

It's always been my understanding that 461X/461 heads had 60-61 cc chambers with the "standard" 1.94/1.60" valves. With the 2.02/1.60" set that included the unshrouding cut on the inlet side the nominal chamber volume was about 64cc.

Eliminating the spark plug side quench areas increased the standard valve head chamber to about 62 cc, and the unshrouding cut with the big valves yielded 65-66 cc.

Some quote the NHRA minimum head chamber volume, which is available on the Web, but that "minimum" allows a "cleanup cut" on the surface, so it's less than the typical as-built by Chevrolet volumes.

Where did you find the specs from GM?

Duke

[David L.]

Re: C2 Head Question

Generally the casting year has 2 digits for blocks, heads, and intakes made in Tonowanda, however, a few years ago I sold a pair of "3782461" cylinder heads dated "H 20 5" (Aug. 20, 1965) and "H 3 5" (August 3, 1965). Each cylinder head had a large "T" for Tonawanda.

From 1987 to 1990 I owned a nice early 63 Split Window Coupe (VIN # 1450) that had never been crashed (all original body panels except for an after market hood) that had a 1967 Chev. 327 engine. The casting numbers on both cylinder heads were as follows:
"3890462", "I 8 6" (Sept. 8, 1966), "GM 6" and "T".

Dave

[David L.]

Re: C2 Head Question

The cylinder head used for 1966 L-79 was GM PART NUMBER 3853608. The same cylinder head PART NUMBER was used for 1967 L-79. As far as I can tell, the GM PART NUMBER 3853608 cylinder head was manufactured from both the 3782461 and the 3890462 castings. Since the part number was the same, GM would have considered the cylinder heads the same regardless of which casting they were manufactured from.

Joe,

I agree with you . My 10/64, 1/65, 5/65, 10/65, 4/67, 7/67, 10/67, and 10/68 Chevrolet Parts Catalogs list GM # 3853608 (Gr. 0.269) as the part number for cyl. heads for 64-67 Corvettes w/SHP, FI (327) with a description "Ident. No. 3782461". I'm not sure when the change took place from the 3782461 head to the 3890462 head in the foundries. The earliest 3890462 head that I have seen was dated "C 1 6" (March 1, 1966). GM # 3853608 was discontinued in Nov. 1968 and replaced with GM # 3928455 so I would assume that all the 3853608 heads made from March 1966 to Nov. 1968 (or probably much earlier) would have a casting number of 3890462.

Note: The lower HP heads w/smaller valves, GM # 3817681, are also described as "Ident. No. 3782461".

Dave

[Joe L.]

Re: C2 Head Question

I've never seen any GM specs for head chamber volume. Most AMA specs list TOTAL combustion chamber volume.

It's always been my understanding that 461X/461 heads had 60-61 cc chambers with the "standard" 1.94/1.60" valves. With the 2.02/1.60" set that included the unshrouding cut on the inlet side the nominal chamber volume was about 64cc.

Eliminating the spark plug side quench areas increased the standard valve head chamber to about 62 cc, and the unshrouding cut with the big valves yielded 65-66 cc.

Some quote the NHRA minimum head chamber volume, which is available on the Web, but that "minimum" allows a "cleanup cut" on the surface, so it's less than the typical as-built by Chevrolet volumes.

Where did you find the specs from GM?

Duke

Duke-----


They are included in Alan Colvin's books "Chevrolet By the Numbers". Supposedly, his specs are sourced from GM blueprints and specifications. In fact, many GM blueprints are included in his books.

[Joe L.]

Re: C2 Head Question

... so I would assume that all the 3853608 heads made from March 1966 to Nov. 1968 (or probably much earlier) would have a casting number of 3890462.

Dave

Dave------


Yup!