whats better J or X heads

ir3333 said

no 340 came from the factory with 10:1 compression.The factory ratings allowed you build to 10.2 or 10.5:1 to be NHRA legal. An early 340 with stock 71 or 72 cc X heads when new was around 9.6:1 or a little less.
I don't think an iron head, 10.1 : 1 340 would run very good on 91 or even 93 octane.

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Never ever did I see the 340 advertised as having a 9 to 1 compression ratio. The early 340 s were advertised as having a 10 to 1 compression ratio and the 72 and 73 were advertised as having an 8.5 to 1.

What they may have actually had and what was advertised May differ. But the factory never advertised it may actually be 9 to1 even though we're saying 10 to 1.

Have a Happy New Year.