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Old 02-18-2020, 08:50 PM
ejgoat ejgoat is offline
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Default 670 heads

A friend has a 1966 389 and wants to put 670 heads on it, we're being told they will not fit unless the Pistons have to be relieved for valve clearance, do you guys know for sure

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Old 02-18-2020, 09:26 PM
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Not with an 068 cam

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Old 02-18-2020, 09:53 PM
Chief of the 60's Chief of the 60's is offline
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Common upgrade swap back in the day.

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Old 02-18-2020, 10:25 PM
PontiacJim1959 PontiacJim1959 is offline
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Depends on how high the lift of the cam is.

The valve angles changed as did the valve spacing - moving them further out. A problem could also arise with the block chamfers and/or the valves hitting the cylinder walls.

If bored .060" over, then you have the same bore size as a 400CI and less of a problem, you may just get away with checking valve to cylinder wall clearance.

Note page 3 of this article as it speaks about the valve/piston difference.
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Old 02-19-2020, 07:13 AM
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steve25 steve25 is offline
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Also all will be well if a Cam lift of no more then .425" is run and the heads and or deck of the block have not been milled more then .015".

This assumes a Fel Pro crushed head gasket .

Also note the need for 400/ 428/455 5.130" lenght push Rods with the swap over.

Also if a valve job had been done on the heads and original valve you will have some .020" of additional valve notch to piston clearance, if I valve job was done and new valves used then you may have only .010" of added clearance.

At any rate the head should be sat on the motor with the Cam to be used and the correct push Rods along with no head gasket to truly see how the tolerance stacks up and nail down what the motor really has for piston to valve clearance.

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Last edited by steve25; 02-19-2020 at 07:18 AM.
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Old 02-19-2020, 12:10 PM
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I ran 670s on an early '70s 350 block with the chamfers. XE256 cam, which is .455 lift on a 110LSA. I set the heads on with checking springs with piston at TDC and checked how far valves would open before it hit something. I put a dial indicator on the retainer and opened it until it hit. Back up .075" min and there's a ballpark for what peak lift will work. As I recall, I had over .500" lift at TDC before the valve hit something.

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Old 02-20-2020, 03:18 PM
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As Paul K stated, with a stock 066-067-068 camshaft, no worries. They will bolt right on and clear the pistons just fine. BTDT.....

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