How much does the head chamber cc affect the compression ratio.
?

I'm working on a 78 motorhome 440. It has 452 heads, research says about 90cc.
I also have some 906 heads, research says 88cc.

Looking at aluminum heads, choices are 74cc, 80cc, 84cc.

Using the stock pistons, what sort of compression ratio will I be looking at with the various chamber cc sizes.

I'd like to see 9.5:1 if possible. Nice NA street and cruising pump gas motor.

FOR accurate #'s you would need to measure the piston to deck height.

Actual CR for a stock 78 440 out of a motor home will be in the 7.7-7.8 range.

You’ll have to work at it to get to 9.5:1.

How much does the head chamber cc affect the compression ratio?

There are only 2 dimensions: chamber volume (including in the casting, deck clearance, gasket thickness, valve reliefs, compression dome) and displacement.
(CV + D) ÷ CV = CR

Plug and chug baby:

http://www.wallaceracing.com/cr_test2.php

Your piston is probably 0.160 below the deck.

Wow. I didn't realize they were that low. I may look into some pistons.

Maybe something stock size from a late 60's.

Simple cast piston if they can be had fairly cheap.

I don't think this is going to need an overbore, probably just a good dingle ball hone.

What you could do is get a set of 75 cc E street heads mill them around .025" and use the factory steel shim head gasket and get just a little over 9 to 1 compression ratio, that way you can leave the pistons alone if the bore looks good.

hi

those pistons are prob .150+ down the hole .!

soooo no matter what head you use you will not have any quench ! = poor performance !

change those pistons !!!!

This^^^

So browsing Summit they have an OEM style replacement piston fot the 1970 440. Would this be an acceptable choice?

I haven't had the pleasure of specing pistons before. So a few of the specs they list are greek to me.

Take a look at the forged Fel Pro, Seal Power, maybe Speed Pro 1970/ 1971 Six Pack replacement pistons, they should give you 9.5 or so with 84 CC heads and stock 440 rods
I would bet money that they will be between .035 to .015 down in the cylinders with no block decking

That piston will be 0.110" in the hole.

The compression height dimension is what you want to pay attention to when comparing pistons and looking get close to deck hieght. That is the distance from the center of the wrist pin to the top of the piston. A bigger number puts the top of the piston closer to the deck, but you need to know where you are starting from.

The 915 head is the last "closed" BR/B chamber, the 1965-67 440 piston has a quench compression distance w/o regard for saving the whales (what the 1968-* open chambers were designed to do).

Math:
440 deck height 10.725"
RB rod 6.76"
50% of stroke 1.875"
Compression distance for zero deck with a closed chamber (gasket thickness as the only quench distance) 2.09"

To expand choices, Cometic has gaskets starting at .027 in small steps all the way to .120 thick. I use a .027 Cometic and pistons in the hole .018 to get .045 quench in my race motor. That also helps cut down on crevice volume where fuel gets jammed into the edges of the chamber at TDC.