Be gentle, but I have a question I'm sure many of you know the answer, but after searching I've yet to find it. I've got a '72 motor home 440 that according to the serial number was an 8.2:1 compression ratio engine. The heads are being replaced with my set of Stealth heads. I'm just trying to get a decent idea of what kind of compression those heads will give me on a stock 440 of that era. I figured since it was in stock configuration, someone would know how much of a jump the Stealth heads are worth.

To start with you need to measure how far down the piston is @ TDC from the deck, most of those are less than 8 to 1 stock

Ok, let me put it this way. How much will a Stealth head raise my compression over a stock open chamber?

Without CCing everything & if you use the same factory thin gasket, maybe .2 ish increase in compression, could be a little more

You won't know without measuring. The factory heads were not known for precision. The reported chamber size is often lower than what they actually measure. Same with the compression ratio and the deck height. Complete crap shoot unless you measure the parts.

Not enough to matter is the answer you're looking for.....You need to change the pistons to make a motorhome motor a HP engine.

Was afraid it wouldn't be much. But, it's what I have to live with until I can build a different 440.

Those stock heads normally measure out around 93 to 97.0 CC, take those numbers and plug in the normal motorhome piston deck height of -.100 to-.120 with a .017 thick head gasket with a bore size of around 4.440 and see what computes.
On your deal I would look at buying the cheaper Eddy 75.0 CC heads or maybe even some small combustion chamber Speedmaster heads
Plug the 75.0 CC into the formula versus the 80.0 CC of the Stealth heads and go from there

https://diamondracing.net/p-10-compression-calculator.html Here's a good calculator once you get some numbers to plug in.

Well for now, I need to run the Stealths that I have. I spent my motor building budget on a 451 that blew up because of an incompetent machine shop.

Could you mil the Stealths to pick up some compression?

My stealths from 2012 were 79-82 CC out of the box. This should be worth around half a point of compression depending on the exact specs of your engine if you run a steel shim gasket. If you run a standard .039 gasket it will only be worth around a quarter of a point. A .016 cut on the Stealths will get them down to the 75 CC range, which will get you about 1 full point with a steel shim and around 3/4 of a point with a .039 gasket.

I run Mr Gasket steel shims with my stealths and have not had a problem. Make sure you look closely that the gasket doesn't overhang the chambers no matter which gasket you run if you run a 4.41 bore gasket.

Measure how far in the bore your pistons are with a straight edge and some feeler gauges and you can calculate more precisely where you should be. I'm assuming you're about .140 below deck and 8:1 stock with a 90 CC chamber.

"incompetent machine shop"? Lord forbid! we know they're all motor messiah's! on a non-sarcastic note, I did some math on compression ratio vs cc's some years back and basically one cc will change the compression ratio about a tenth of a point. having a compression ratio lower than 9:1 will need just a little more than one cc for a tenth of a point, and compression ratios at around 10:1 will need slightly less than one cc for a tenth of a point in change. you'll never know the "exact" change without measuring everything but you can get close using the one cc/ tenth of a point thing.

Eventually, I will learn this valuable skill: if I don't say anything at all, the chances of being wrong are slightly reduced.

Maybe I missed it, but I didn’t hear the OP saying anything about quench.

Never say never! Just mill away the deck surface of the head, but leave "quench pads" that hang down to .040" above the piston. I've done it, it works surprisingly well.

Improper upper ring gap for the KB pistons, and didn't resize all the rods after installing ARP bolts. 7k later it blew up.

In my experience the typical motorhome engine pistons are .150-.155 in the hole. Stealth heads are 80cc ish.
The engines I’ve measured are more like 7.7-7.8 compression. Not the advertised 8.2.
I’m currently doing one with trick flows and had it decked .040. With a standard gasket I’m up to a whopping 8.9.
With your deal you’ll be around 8.3-8.5. If you use a thin gasket maybe a little more.
It’s something you’ll just have to live with if you don’t want to rebuild the short block.

Well, if I'm not rebuilding it once a year it will be an improvement right there.