312 heads on 239 cid y block

As John points out, the ‘G’ heads were available on the 272’s and the only issue with running them on any Y engine would be when running the valve lift much higher than stock. By design, the intake valves on the Y-Block heads are positioned such that they will hit the cylinder walls thus preventing them from free dropping into the cylinders. While this has likely saved many an engine from catastrophic failure, this does limit the amount of amount of valve lift you can safely accommodate without taking appropriate corrective action.

For Y builds using oem iron heads, I use the 0.535” intake valve lift number as the maximum lift that can be used without having intake valve to cylinder wall clearance issues. Any intake valve lift values higher than that requires that the cylinders to be notched for intake valve clearance. Here’s a picture of what happens when you put too much lift where the cylinder has not been notched to accommodate it. That’s easily corrected by simply notching the cylinder walls appropriately. Just don’t notch too far down where the top ring rides in the cylinder bore.

http://forums.y-blocksforever.com/uploads/images/3b845806-2ded-482b-8d4a-6e11.jpg

And here’s a picture of the notch that alleviates the problem.

Lorena, Texas (South of Waco)

Author	Message
ghancock	Posted 4 Years Ago
Hitting on all eight cylinders Group: Forum Members Last Active: 4 Years Ago Posts: 4, Visits: 41	Thanks!
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Ted	Posted 4 Years Ago
Co-Administrator Group: Administrators Last Active: Yesterday Posts: 7.2K, Visits: 203.0K	As John points out, the ‘G’ heads were available on the 272’s and the only issue with running them on any Y engine would be when running the valve lift much higher than stock. By design, the intake valves on the Y-Block heads are positioned such that they will hit the cylinder walls thus preventing them from free dropping into the cylinders. While this has likely saved many an engine from catastrophic failure, this does limit the amount of amount of valve lift you can safely accommodate without taking appropriate corrective action. For Y builds using oem iron heads, I use the 0.535” intake valve lift number as the maximum lift that can be used without having intake valve to cylinder wall clearance issues. Any intake valve lift values higher than that requires that the cylinders to be notched for intake valve clearance. Here’s a picture of what happens when you put too much lift where the cylinder has not been notched to accommodate it. That’s easily corrected by simply notching the cylinder walls appropriately. Just don’t notch too far down where the top ring rides in the cylinder bore. And here’s a picture of the notch that alleviates the problem. Lorena, Texas (South of Waco)
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312 heads on 239 cid y block

312 heads on 239 cid y block

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