K Head and Ka head differences?
Old(s) Fart
Joined: Mar 2007
Posts: 50,768
From: Northern VA
The "warranty replacement" story is not quite what it seems. GM routinely superceded part numbers in the parts network as older stocks ran out and were replaced by later articles (witness the "dimpled" 1971 front fenders being shown as superseding the 1970 flat fenders). That does NOT mean that the new replacement part number is identical to the old one, only that it will work to keep the car running. For a few years following the model year of production, the same factory style heads were still available in the parts network - D, F, and H heads could be purchased over the counter. By the mid-1970s, the only BBO head castings left in the parts network were the J and K/KA castings. J heads were shown as superseding all regular-performance heads and KA heads were shown replacing all performance heads. This does not make KA heads direct replacements for F or D or H heads. It only means that they were the best replacement available at the time. NHRA stock class specs accept KA in place of the original performance heads because the KA's don't provide any advantage over the originals (which is NOT to say that they don't provide a DISADVANTAGE).
Registered User
Joined: Jan 2020
Posts: 2,890
From: Sarasota Florida
K and KA heads were primarily for marine and industrial uses, but were used on some of the L77 motors in the mid-70s.
The "warranty replacement" story is not quite what it seems. GM routinely superceded part numbers in the parts network as older stocks ran out and were replaced by later articles (witness the "dimpled" 1971 front fenders being shown as superseding the 1970 flat fenders). That does NOT mean that the new replacement part number is identical to the old one, only that it will work to keep the car running. For a few years following the model year of production, the same factory style heads were still available in the parts network - D, F, and H heads could be purchased over the counter. By the mid-1970s, the only BBO head castings left in the parts network were the J and K/KA castings. J heads were shown as superseding all regular-performance heads and KA heads were shown replacing all performance heads. This does not make KA heads direct replacements for F or D or H heads. It only means that they were the best replacement available at the time. NHRA stock class specs accept KA in place of the original performance heads because the KA's don't provide any advantage over the originals (which is NOT to say that they don't provide a DISADVANTAGE).
The "warranty replacement" story is not quite what it seems. GM routinely superceded part numbers in the parts network as older stocks ran out and were replaced by later articles (witness the "dimpled" 1971 front fenders being shown as superseding the 1970 flat fenders). That does NOT mean that the new replacement part number is identical to the old one, only that it will work to keep the car running. For a few years following the model year of production, the same factory style heads were still available in the parts network - D, F, and H heads could be purchased over the counter. By the mid-1970s, the only BBO head castings left in the parts network were the J and K/KA castings. J heads were shown as superseding all regular-performance heads and KA heads were shown replacing all performance heads. This does not make KA heads direct replacements for F or D or H heads. It only means that they were the best replacement available at the time. NHRA stock class specs accept KA in place of the original performance heads because the KA's don't provide any advantage over the originals (which is NOT to say that they don't provide a DISADVANTAGE).
Old(s) Fart
Joined: Mar 2007
Posts: 50,768
From: Northern VA
Unfortunately I don't have that comparison data. I'd suspect that all the BBO head combustion chambers are in the 80-84 cc range as cast, with the possible exception of the D heads. Runners are likewise similar except for Js. I'll have to look at my Ks to see if the one crossover is blocked.
Registered User
Joined: Mar 2010
Posts: 1,279
From: Nova Scotia, Canada
Unfortunately I don't have that comparison data. I'd suspect that all the BBO head combustion chambers are in the 80-84 cc range as cast, with the possible exception of the D heads. Runners are likewise similar except for Js. I'll have to look at my Ks to see if the one crossover is blocked.
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