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Discussion Starter #1
I recently purchased a 1970 GTO 455HO. I have been investigating the build details and am a bit stumped by the YH engine and 64 head combination in this car. I have a visual inspection of the the block and heads to confirm the numbers, and dealer order documentation say it is a "4 BBL 455 HO" option code 344.

I have been unable to find any online resource that shows that a YH/64 combo was offered, all the site I have read have YA/64 and YH/15.

Anyone have any better insight??

I am really excited about this great car and look forward to being an active member of this forum. Thanks for the help
 

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64-67 Expert
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Not a '70 expert but am somewhat familiar with the heads. As far as I know, ALL '70 GTO's with the 455 came with the big valve, 87cc #64 heads. The small valve heads for the 455 that year were #15's, and they came on the big cars, but not the GTO. I looked far and wide for some #64's to use on my '67 400 to drop the compression, and had to settle for a set of #15's. They work fine on my 400, and give me about a 9:1 ratio. A '70 GTO with the 455 is a running car....you did GOOD!!
 
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