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  #21  
Old 09-27-2025, 08:45 PM
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66 421 is YJ, 4-bolt STD Cyls yet keen on using 428 STD for the valve relief match to 4X, so block would get .030.

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  #22  
Old 09-27-2025, 08:59 PM
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My thoughts..
Which 4X's?
New Hylift Johnson lifters are not cheap these days, but if that's all that's available, that's what I'd use..
Post a want to buy, here, see what happens.
Might have to use the Tomahawk intake for it's likely lowest carb mount surface to fit under hood.

Carry On!!!

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1977 Black Trans Am 180 HP Auto, essentially base model T/A.
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  #23  
Old 09-28-2025, 08:43 AM
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4X heads show a 1973 cast date. I dunno the stamp but the chambers look >100cc. 2.11-1.66

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  #24  
Old 09-29-2025, 10:18 AM
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I have little 4X knowledge. I know they are crack prone, have at least 2 versions, that's all maybe someone could post how to tell the difference in 4X castings, and the approx chamber volumes.

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1977 Black Trans Am 180 HP Auto, essentially base model T/A.
I'm the original owner, purchased May 7, 1977.

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Buddy, I just shut your Prius down...
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  #25  
Old 10-13-2025, 08:27 AM
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Anybody gots:

428 STD pistons, forged? Rings too? Am i likely to find new?
421 +030with rings?

Large inlet oil pump? Clean-used ?
Dual-Plane manifold with fuel-Inj bosses.

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