572 Hemi, aluminum heads, what’s the highest compression I can run safely on 93 pump gas? I know timing and cam is a factor but just a general rule of thumb idea. Pistons are 10.5 now but I can deck to get more or add thicker gaskets to get less, street and occasional blast down the track by adding race fuel.

Talk to your cam supplier. If you give him your engine particulars and what octane you want to run, if he's any good he can tell you what compression ratio to run. On an AMC 401 I went this route and with iron heads, stock intake and exhaust, running 87 octane pump swill, the recommendation was absolutely no more than 9.2. How did it run? Still putting it together so we shall see.

10.5 might be okay in a wedge with perfect quench. I bet it is too much in Hemi for pump gas.

We have a member here than has ran his 12:1 Hemi on pump gas, but i'm not sure he raced it on pump. From what i have seen, your about max to race on pump gas also, seems Hemi's are not as sensitive to compression increases as wedges are. Best told me you need 13:1 or higher to really make a difference in power with compression increase from 10.5:1. Between 11:1-13:1 seems to be a bit of a no mans land with Hemi's. That being said, I will be running 12:1 with my 572 because i ordered the pistons before i was told better. Best Machine has made 850hp on pump gas with 10.5:1 compression with a 572 Hemi, so seems there really is no need for higher compression for a street Hemi.

We have run 12:1 with our Hemi...I would even go more with an aluminum block.....

The Hemi chamber is actually pretty detonation-resistant; one of the reasons it was employed in the Gen1 engines.
I had an iron-head 426 Hemi @ 10.8 measured, never an issue @ 36 degrees total, + vac advance, even on CA 91 octane.
It did have a fairly big-for-the-time old Crower FT cam, IIRC 247 @ .050, lift in the .540s, which bled off some dynamic CR (and idle vacuum).
With aluminum heads, that engine could have gone more like 11.3-11.5 CR, I'd bet.
4-speed, 4.10s, 3700-lb RR.
I wouldn't push a wedge that far, from personal experience.

Sounds like I’ll leave it, it’ll be down in the hole about .065 anyway..? (haven’t checked the deck) (rods are 7.045) with a 1.36 ch. 56.6 dome 170 chamber, right at 600 cu in. I’ve heard so many ‘what’s’ I wanted some real examples to do once and not go back into and change, thanks all

I'm at 10.4-1 with my 605. It will run on 89.5 but I prefer to run 91.

Elevation is a factor too, the sea levelers will experience problems at lower compression. On the other hand they make more power with the denser air.

a lot of factors go into to building detonation resistance. a hemispherical combustion chamber is more detonation resistant than a wedge chamber. allow for some carbon build-up in the build to be safe.

I wouldn't worry about 10.5 to 1 compression ratio on any aluminum headed Mopar, especially on any hemi motors that have not been CC on the actual dome volume in the cylinders
Hemiroid motors are a completely different animal when it comes to true compression ratio
I've seen hemi pistons with advertised dome volume have 15 CC less when actually measured
Depending on the stroke and bore size that can mean the difference between 12.2 and 10.8, the bigger the motor the harder it is to get the compression up on Hemiroid whiney

I'm 10.0:1 on the dot with iron heads and a pretty small SFT cam on my Hemi. No problems with 93. I wouldn't be afraid to try 11:1.

Static compression has very little to do with what octane fuel your engine needs, it is dynamic compression or cylinder pressure that determines much more the octane needs of an engine. Performance trends engine program will make a prediction on spark knock and will generate a spark curve to use if knock is predicted, very cheap insurance when designing an engine build. I have built pulling truck engines that had to run on pump gas with 13 to 1 static compression, and it did not detonate.

Depending on the overall setup of the build, where the compression/quench zone ends up at on the engine, and to remove some worry to make things a little more forgiving, you probably should look into having the chambers softened on the heads.

The Hemi I just sold was 12.3 and had zero detonation issues on pump swill..Steel block aluminum head.

So you really know where you're stating from, I'd advise to measure the actual 1" down volume subtracted from theoretical flat (to manually calculate your dome volume) along with chamber CCs, and use these to manually calculate your CR....before you order gaskets.

Closing the intake valve later to reduce CCP works at cranking and low RPM, but its effect on anti-knock is gone well before your torque peak.

^^^This is what we did with my dads 528 pump gas HEMI. 12.5 on 93 and he beats the hell out of it and still going after 8 yrs.

Controlling cranking compression can help with pre-ignition. Compressing a gas increases its temperature. Starting with a colder intake charge also helps.
Detonation is an uncontrolled combustion event which occurs after the spark event. Chamber / piston shape, spark plug location, and quench distance can help or hurt.
Either way, you want to avoid hot spots in the chamber and on the piston.
There are a bunch of dynamics that I don't understand. As RPM goes up in may reduce the chance of detonation, but not sure how the relationships of Time (decreasing with RPM) vs Air/exhaust flow (increasing with RPM) vs Engine load (how fast the RPM is changing.) I think the slower reving engine (think heavy truck) us going to build more chamber heat than a light vehicle with the same power.

So it makes it hard to compare just compression ratio vs. octane as there are a bunch of unknown variables.

“chambers softened” Not sure what this means