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By Brent - 7 Years Ago I have a single head marked ECK-C on the outside and ECK-B on the bottom.  John's Head chart indicates the CR is slightly different.. How can I determine which marking is correct (The ECK-C or the B) Does the Compression Ratio translate to the CC size? If so, how is the CC measured? If one ECK-B and one ECK-C were installed together on a 292, would the 5% CR difference cause an imbalance? By KULTULZ - 7 Years Ago Brent Posted - "I have a single head marked ECK-C on the outside and ECK-B on the bottom.  John's Head chart indicates the CR is slightly different.. 63% of original size (was 800x190) - Click to enlarge How can I determine which marking is correct (The ECK-C or the B) Does the Compression Ratio translate to the CC size? If so, how is the CC measured? If one ECK-B and one ECK-C were installed together on a 292, would the 5% CR difference cause an imbalance?" Actually, both Casting ID's are correct. The ECK-C head was modified from a ECK-B casting, most likely calling for a different machining protocol (decking) for decreased chamber volume. The ECK-C ID's it as a higher compression head. A DATE CODE could further narrow it down. You would want the same head style on each cylinder bank. You verify CC's with a burrette. JOHN's chart gives a CC footnote symbol but no footnote. By darrell - 7 Years Ago i put these very 2 heads on a 292 years ago.i didnt know they were different until after i bought them.the engine ran fine. By Brent - 7 Years Ago KULTULZ  I have not been able to crack the date coding. Can you tell what date this head was manufactured? #'s under valve cover: # under exhaust outlets: Data on face (There is an A5 under the X-out: By darrell - 7 Years Ago theres a couple of things you could do to measure the difference get a measuring device and turn the heads over put the plug in and fill them with water and measure the difference.another thing would be to shave more of the larger one to match. By KULTULZ - 7 Years Ago Brent Posted- KULTULZ I have not been able to crack the date coding. Can you tell what date this head was manufactured? #'s under valve cover: 63% of original size (was 800x190) - Click to enlarge # under exhaust outlets: 63% of original size (was 800x190) - Click to enlarge Data on face (There is an A5 under the X-out: 63% of original size (was 800x190) - Click to enlarge       Your DATE CODE is 5 1 D which would be 1955 - JAN - and D the day of month. The X signifies a modification in the mold and D 4 confirms 4th day of month. Now to have a NUMBERS CORRECT CAR/ENGINE ASSY, the CYL HEAD DATE CODES must be at the same or within a few days as once they come out of foundry, they are machined and then assembled, then assembled to a short. THE ENGINE ASSEMBLY is then shipped to whiscruber vehicle assembly plant it is on order for. Theory only as many things can happen within the process. This is how you would document the engine for sale, by keeping a concise build sheet to go with the car. Date Casting Code - 1st Character Indicates Year - 2nd Character(s) Month - 3rd Character Day By Brent - 7 Years Ago Thank You KULTULZ The engine that I recently acquired has heads that are forged a day apart and then installed on the short that was forged nine days later. I think the factory made an error; must have been a good New Year's Eve party. Bummer By KULTULZ - 7 Years Ago Brent Posted- "The engine that I recently acquired has heads that are forged a day apart and then installed on the short that was forged nine days later. I think the factory made an error; must have been a good New Year's Eve party. Bummer" Nah, you're OK. Close enough time frame. Remember the heads have to be machined and assembled. By Brent - 7 Years Ago The error that I speak of is: This ECK-B block has one ECK-B and one ECK-C, mismatched heads. The engine seems to be a factory error, not a head replaced down the road. By KULTULZ - 7 Years Ago Brent Posted- "The error that I speak of is: This ECK-B block has one ECK-B and one ECK-C, mismatched heads. The engine seems to be a factory error, not a head replaced down the road." OH... That makes the discussion quite different. In other words, your engine has both... By Brent - 7 Years Ago Yes. What a bummer. I am now searching for an ECK-C to match the (5 1 D) code, within a couple days as you have mentioned will be correct. By KULTULZ - 7 Years Ago Now that is going to be an exercise. Most will not understand DATE CODE or the desire for NUMBERS MATCH. GOOD LUCK with it and let the board know how you do. OH! The A5 is most likely the MOLD NUMBER. That will/may not be as important.