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post #1 of 6 (permalink) Old 11-10-2018, 07:42 PM Thread Starter
 
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hello i have a 1965 gto 421 engine i need to know i have put a set of 6x heads on it push rods seem about 1/2 in too short. it is my understanding
that the heads will not work without some mods to pistons or do i just need to get longer push rods thanks
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post #2 of 6 (permalink) Old 11-10-2018, 10:41 PM
 
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welcome

Pushrod Lengths

Scott

that wont work I believe .... never tried it ... but never heard of it done either

what are you trying to accomplish ?

more info needed ... you have NO early heads ? trying to drop the compression ?

rebuiding ?

Last edited by BLK69JUDGE; 11-11-2018 at 01:22 PM.
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post #3 of 6 (permalink) Old 11-11-2018, 07:41 AM Thread Starter
 
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6x heads

so if i just install longer push rods i wont have any valve interferance?
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post #4 of 6 (permalink) Old 11-11-2018, 11:34 AM
 
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Originally Posted by mikeymo View Post
so if i just install longer push rods i wont have any valve interferance?
If the 65 421 has original style pistons you will have a problem. Pontiac changed the valve angle on the heads starting in 1967 I believe. When they came out with the 400. There's a few articles here if you do a search.

I could be wrong but im pretty sure that the 6x heads will not match up with the valve reliefs on your pistons.
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post #5 of 6 (permalink) Old 11-12-2018, 11:02 AM
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Originally Posted by My65goat View Post
If the 65 421 has original style pistons you will have a problem. Pontiac changed the valve angle on the heads starting in 1967 I believe. When they came out with the 400. There's a few articles here if you do a search.

I could be wrong but im pretty sure that the 6x heads will not match up with the valve reliefs on your pistons.
^^^^ What he said. This change is the reason for the infamous "double eyebrow" pistons that look like the ones in the first photo below.

They are intended to fit both early and late style heads, but you do not want these for any serious engine build.

Better to make sure the heads and the pistons match up correctly.

Bear
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post #6 of 6 (permalink) Old 11-15-2018, 03:48 PM
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You CAN fake it and run late heads with the early piston valve reliefs IF IF IF you check the clearances. The camshaft lift and duration has a HUGE impact on this. If running a stock-ish cam like the 068, you probably will not have any issues. But you need to check it out first. (modeling clay, etc.) I have run '67-up pistons in a 389 with the stock 389 heads and had no issues. But my cam wasn't overly aggressive. ('66 389 bored .060" using std. bore 400 pistons). Before the advent of good aftermarket pistons, this was pretty common back in 'the day'.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Complete Engine Compartment Discussion

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