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Discussion Starter #1
Can anyone tell me if there is any difference in the 69 XX2BBL and YS 4BBL Blocks. I know the heads are different but are the bottom ends the same?:confused
 

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67 Basket Case Restorer
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Yes and the pistons may be the same too as Pontiac used the combustion chamber to alter the compression ratio.
 

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Discussion Starter #3
Thanks Mitch, so a 69 XX Block with a set of 71 66 Heads from a 455, should give you the roughly the same HP as a standard YS 4BBL Factory 400 GTO?
Would that be correct?
 

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Former Moderator
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Thanks Mitch, so a 69 XX Block with a set of 71 66 Heads from a 455, should give you the roughly the same HP as a standard YS 4BBL Factory 400 GTO?
Would that be correct?
If I'm reading my information correctly, I would say no. A '71 #66 head is chambered at 114cc(low compression), whereas, a '69 head ranges from 56cc - 94cc(higher compression). I guess I would take any '69 head over a #66 head with exception of the 56cc. That was on a 303ci RA V tunnel port(didn't know they made one). The compression would be way too high on a 400. The lowest chamber you'd want to go would be a 72cc head.
 

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64-67 Expert
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I just sold a set of 66 heads...(1971 455 114cc). I had them on my 400, and they netted me about 7.2 compression. Regular gas, yes, but they were too low of a compression for the 400. The guy I sold them to is putting them on a stroked 455, so they'll be perfect for him. On a 400, with today's gas, you need about an 80--90cc chamber head, or to use slightly dished pistons with the stock high compression 72cc heads. The 2bbl blocks and 4bbl blocks are the same.......only the camshaft and intake were different. Good luck.
 
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