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840 & 291 heads on same car?

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Discussion starter · #1 · (Edited by Moderator)
Found this on eBAy today. I think I have seen this one for sale before. By the vin # it looks to be a late 69 car. No trim tag to look at and though I like the car, a few things catch my attention. Biggest item is the 2nd picture showing the list of numbers on the side glass. Has a pn and date for the 2 heads and if I am reading right, 1 is a 840 and the other is a 291. Can that be? Isn't 840 a closed chamber head and 291 an open chamber requiring differant pistons? The print is small and I do have my reading glases on. If I have misread please excuse me.

Loren


http://cgi.ebay.com/ebaymotors/Chev...-CAMARO-SS-L78_W0QQcmdZViewItemQQcategoryZ6161QQihZ017QQitemZ270020495153QQrdZ1
 
#3 ·
No, the 291 did replace the 840 for L-78 and L-72 late in the extended model year. The 291 has a slightly larger volume, so the compression would be slightly lower on one side. I doubt that the factory would intentionally mis-match the heads, but I guess it's possible. I saw that ebay add, too, and just assumed the car was "put together".
 
#5 ·
The 291 head is also a closed chamber head. This head is unusual in that it is the only square port head made with a closed combustion chamber using the small 5/8 spark plug. Used exclusively on the 70 LS-6. Before this head, all closed chamber heads used the 13/16 spark plug. After this head there were no more closed chamber heads and all open chamber heads used the 5/8 spark plug.
 
Discussion starter · #6 ·
Obviously if both are closed chamber I still can't imagine Chevy mixing part numbers especially with differant spark plug hole size. This issue for me calls into question an otherwise good looking car. But then I don't have the cash to go down that road anyway. Mike, You said the 291 was used exclusively on LS-6's. I own a 1970 L-78 402 engine out of a Baltimore built Chevelle that has a 854 block cast H 5 9 (August) with a T1121CKO on the pad (Nov 21). The heads that came with this block when I bought it back in 1982 are 291's with cast dates of K 3 9 (November).

Loren
 
#8 ·
I just checked so I would not have to go by memory. Chevy By The Numbers lists the 291 head for Chevelle, Nova and Camaro for 396/375 HP engines and 454/450 HP engines in 1970 and on 396/375 HP and 427/425 HP for late 1969 models. I forgot about the 396/375 HP use. "This was the last closed chamber square port cast iron head produced. It was produced in both plug designs for service replacement" from CBN. I do a lot of 70 Chevelles and have only seen small plug heads originally installed on those high horse cars

You are right in that GM would not build this engine with 2 different heads. At least one of them has been changed.
 
Discussion starter · #10 ·
What is the differance then between 840's & 291"s? If you have both as closed chamber, large spark plug, do they have differant holes for accessory mounting? This topic could be expanded to ask the question: Does an August-November, or when ever the 1969 Camaro styling ended, L-78/ 4-speed have a JH coded 396 or a CKO coded 402? If it's a 396 why would Chevy put 402's in Monte Carlo's, Chevelles, etc but 396's in Camaro's. And what about Nova's?

Loren
 
#12 ·
Kurt S said:
I'm not convinced that the heads didn't come this way, as long as the spark plugs are the same size.
I've seen several cars with factory mixed heads, esp on midyear changes where fit and function were not affected.
Click to expand...
I owned aa 69 camaro L78 that had one 840 and one 291 and it ran great. I believe the 291 was a warranty replacement based on the date and the large plug configuration. As stated previously, later in the year it was used as a warranty replacement...
 
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