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Just to confirm the results of this thread, I searched for and found where John Z Hinckley replied to a question in March 2006 in the CRG board about the significance of the 'X' on heads . He said...
"A friend who has spent his entire career at the Saginaw foundry says the "X" is meaningless - just a foundry marker - on all small-block heads except the 461's, where the 461X had a 15cc larger intake port."
Those who know of JohnZ will appreciate his input.
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BamaNomad(er)
'55, '56, '57 Nomads North Alabama area Gary
In 62 the 327 double hump 461 X Fuelie heads were the ones to have . I believe they also were on the 340hp SHPE in the Corvette. The Fuelie cars were rated 360 hp.
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"I'm Goin' the distance, I'm goin for speed." Cake
I'll go along with the others that said the 461X heads are the only "X" heads that were truly different from their "non-X" counterparts, at least to my knowledge.
They had about 170cc intake port volume, where all the other "camel hump" heads only had 155cc. In fact the only other production SBC iron head that had 170cc port volume was the Vortec 350 head. They were produced in 1962 and 1963 on 327 engines that had the 300, 340, and 360 hp ratings. They did not have the 2.02/1.60 valves though. The heads were sought after for NHRA racing in the Modified and Comp classes that required a straight plug iron OEM head in the 70s and 80s, and didn't allow anything but bowl porting. I ran such a class, and spent a fair amount of time looking for some. They were worth about .15-.20 et on my dragster.
I'll go along with the others that said the 461X heads are the only "X" heads that were truly different from their "non-X" counterparts, at least to my knowledge.
They had about 170cc intake port volume, where all the other "camel hump" heads only had 155cc. In fact the only other production SBC iron head that had 170cc port volume was the Vortec 350 head. They were produced in 1962 and 1963 on 327 engines that had the 300, 340, and 360 hp ratings. They did not have the 2.02/1.60 valves though. The heads were sought after for NHRA racing in the Modified and Comp classes that required a straight plug iron OEM head in the 70s and 80s, and didn't allow anything but bowl porting. I ran such a class, and spent a fair amount of time looking for some. They were worth about .15-.20 et on my dragster.
To add ...they were a must in the Corvette judging world of NCRS for the 62 SPHP and Fuelie cars.
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"I'm Goin' the distance, I'm goin for speed." Cake
Yes, in a way, that's because they were the only date correct "camel hump" heads in 1962 and 1963. "Plain" 461 castings didn't exist until the 1964 model year.
But, how is an NCRS judge going to see that on an assembled engine? You can't see the date code or any relevant casting marks with the head on the engine and the valve cover on the head. Even with the valve cover off, you can't see the "X" designation - but you can see the date code.
In 62 the 327 double hump 461 X Fuelie heads were the ones to have . I believe they also were on the 340hp SHPE in the Corvette. The Fuelie cars were rated 360 hp.
I have these double hump heads on my 55 with big valves and ported, but they don't compare to some of the new head designs for power
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