Compression ratio for 1966 440. Stock heads vs 452s?

Friend has a '66 New Yorker with stock 440. Years ago one of the heads cracked (over heated) so he replaced both with a rebuilt set of 452s. After that he believes he lost quite of bit of power (seat of the pants measurement). This is the non-HP 440 from '66. First of all what heads did it come with from the factory? What cc are those heads? How far down in the hole would stock non-HP 440 pistons be in the block? Trying to guesstimate compression.

He believes that the difference between open vs closed chambered heads are the reason for his power loss. What do you think?

That cyl head change .... would lose a TON of compression !

Head cc's ? .. some 452's can be high 80's/low 90's .... the early heads ... low to mid 70's.

Not sure how far in the hole the slugs were on a 66, But....

I had a non molested hp 67 440. The pistons were .065 in the hole IIRC. Then the .020 gasket and some 516's that cc'd around 79.

Comp calculator gives that just over 10:1

Switch to 452's and a felpro gasket, and you're down to just under 9:1.

So a full point of compression, but you did gain a bigger exhaust valve and bigger runners in the heads. So there is a debate unto itself there.

Realistically, the gains in a closed head are only seen when quench is present. With pistons that far in the hole, you have no quench.

A full point of compression should only cost you 3 to 4 % but I think there are some other variables here.

Some say that a closed head develops some swirl on the intake charge, that improves atomisaton.

So it could be that with the open heads, it became slugish down low due to poor atomisation of the fuel charge. Add on the slight overall power loss because of the comp loss, and it may be noticable in the pants dyno.

Maybe the 452s had a crappy valve job...

FWIW I've seen the dyno numbers & I know they say one point of compression is only 4% but that is at max output, seat of the pants that one point of compression has always felt stronger from off idle to max power...

Also, the valves in the 452s are bigger, and the ports are bigger/higher flowing than what's in the -516 heads that were original to the '66. Adds up to lower port velocity, which probably reduces turbulence and makes for a less ideal burn.

I'd say that, coupled with the compression loss, is the reason. Assuming the -452 heads were in good condition, of course...

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Also, the valves in the 452s are bigger, and the ports are bigger/higher flowing than what's in the -516 heads that were original to the '66. Adds up to lower port velocity, which probably reduces turbulence and makes for a less ideal burn.

I'd say that, coupled with the compression loss, is the reason. Assuming the -452 heads were in good condition, of course...

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yes but do you need all that flow when you are only spinning it up to 4800? The heads would help more top-end. He has lost all his low-end grunt.