Cylinder head volume and compression ratio.

[AussieRT]

G'day. Need some help regarding compression ratios. Recently learned that my 440 is a 1976 HP version. Best I can find is that they run 8:1 comp ratio, and thus make less power than earlier models (I am also aware of the change to how they read hp in the later years).

My question is, can it get to 10:1 comp levels by changing the heads alone, or will I need to change pistons aswell?

Also, what are the stock volume (in CC) of the factory cylinder heads?

Cheers

[nqkjw]

You can't believe any manufacturers figures so you probably have to lift the heads to measure how far down the pistons are and go from there.
Assuming 8:1 is correct you'd need some pretty small chambered heads to get 10:1.
For example I changed the heads on my 440barracuda from 906's to 915s.
From memory the pistons were 100 or 120thou down the bore,i think 906s are 88cc chamber and 915s are 80cc chamber?
Anyway,at the time I measured it all accurately and I had 8.2:1.With the 915s on tin shim gaskets I got it up to 9.3:1.

I THINK stock 76 heads would be 452s at 88cc?
Someone else can correct me if I'm wrong.

[Strawdawg]

sounds right to me.  I suspect it is actually lower than what the factory claimed because the piston is way down the hole on most of them as he pointed out above.

If you actually had 8-1 and went to 9.5-1, and you currently were making 350 hp, you might gain around 17 hp according to the charts and calculators...peak hp.

You might gain more at lower rpms.  In real life, it depends on the total engine combination because higher ratios allow you to run a bit bigger cam and not lose as much on the bottom end and gain more on the top end.

As one continues to raise the compression ratio, the percentage of improvement  diminishes.

[HP_Cuda]

This motor seems to be the perfect candidate for a blower....

[AussieRT]

thanks for all the info so far. Anyone know the CC's of the 1976 dished pistons?

[Chryco Psycho]

They are not dished just short , usually about .125 below deck & to make it worse the deck is generally higher than advertised

[74 challenge]

This motor seems to be the perfect candidate for a blower....

I thought exatcly this.

Time to build a twin turbo set up.