What is a safe compression ratio to run with pump gas?

I am currently running 11.5 compression with a stage IV fully ported and milled (68cc) iron head.
The heads have been on the motor for years and are leaking oil down the valve stems and I need to pull the heads and repair them.
The motor pings on pump gas and being that I will pull the heads off I am going to increase the thickness of the head gaskets to lower compression to make it more pump gas friendly.
Here is what I am running now.
R/B block 4.25 stroke 4.35 bore
.613 lift 278 @ .050 cam in at 105 degrees.
Tunnel ram with 2 750 Holley carbs
4500 stall converter with 4.10 gear.
All in a heavy B Body

Is 10.0 compression still pushing it? Or should I aim for la lower number.
Thanks in advance for your help.

For a heavy street car I'd say 10:1 is the max. If I was building the engine I'd probably shoot for 9.8 compression using a reverse dome piston and tight quench.

I read an article about doing this the other day, and the gist of it was you can actually make the engine more knock prone by lifting the head with a thicker gasket and increasing the quench distance, even with a lower overall compression ratio.
Whats the tuning like?

I don't like putting more area between piston and head because you could loose some quench..... there is a reason why the late 70 motors detonated on 8.5:1 Maby try a bigger cam or else you could take away some timing....

What quality, octane rating, gas are you wanting to run and if it is ethanol how much % is in it?

increase the thickness of the head gaskets to lower compression
Don't.

Static compression ratio is simply a static measurement of the volumes of the cylinder at top and bottom dead center, and is only one factor in running an engine on low octane fuel. How much cylinder pressure actually happens in the cylinder and the cam timing events are much more important. For example I built several engines for some truck pullers several years ago, who had as a class rule pump gas only, I used 14 to 1 dome pistons in those engines, they worked very well. A good engine program will tell you much more about if your combination will work. Their are several, I use performance trends, it will calculate if detonation will be a problem and calculate a timing curve to allow you to make the engine live. When I do a pump gas build, I plug the numbers into the program, get the timing curve, and then set the distributor up in a distributor machine to match, it is in the ball park every time I have done it. I have even used this method to set up initial timing maps for boosted applications with electronic fuel injection. The program allows you to enter the octane fuel and the amount of boost, and it will tell you how much you need to retard the timing through the curve. And with the cost of engine parts and machine work, around $100.00 is a small price to pay, plus it's fun to waste time with on rainy days as well. And with any computer program is garbage in garbage out, you have to take the time to accurately enter the parameters of your engine, wild guesses will not get it. I use Pipemax as well, especially in building headers and picking intake manifolds.

On my 440 based street/strip 500" engine, I ran right at 11:1 for years on pump gas with no problems. That was with good quench. Your cam and converter will help you. As already covered, don't sacrifice quench in order to lower the CR.

P.S. That was with aluminum heads.

SB Mopar (360), hydraulic flat tappet cam (Hughes Engines HE3844AL cam, .535/.540 lift, 237/243 dur. @ .050", 286/290 adv. dur., 108 LSA.), 10.7:1 static CR, open chamber factory '596 head castings, heavily ported, chambers polished up and literally no quench volume to speak off (meaning it's absolutely dismal by all accounts, I have about 0.090" between piston top and chamber floor).

Previously was at 9.7, did a head re-surface to get to 10.7, my cranking compression went from 165 to 185-190 psi.

I run 91 octane pump-gas now, was previously running 94 but went lower to try this out, aggressive ignition curve (21 @idle, 35 in by 2000RPM).

Rest of drivetrain probably gives me some room (and is forgiving), this is a street car (3600 lbs), but 4K converter and 4.10 gear, so off-idle and part-throttle the motor has some chance to rev up easily and not quite feel the load that may lead to detonation at lower RPM...at least that's how I interpret my results so far (may be off on this...).

Maybe it's time for a fresh set of aluminum heads?

I won't build a pump gas motor with iron heads that has more than 9.75 to 1 ratio, neither should you
My last pump gas motor that made decent power, 727 HP, had 10.78 to 1 comp ratio with a set of Indy SR M.W . heads and a Indy 400-3 intake with a Holley #9375 non HP Dominator, that baby ran really good

I am going to have to bite the bullet and spring for a set of aluminum heads. What compression ratio should i shoot for to run 93 octane????

When it absolutely positively has to run on pump gas....... along with the fact that it’ll probably never go to the drag strip again........ is it really worth pushing the CR envelope?

How much power do you really think you’re leaving on the table if the compression is 10:1 instead of 10.5:1?

And then there’s the question of 93 octane pump gas.
It’s not available everywhere.
Who’s to say how long it will remain available in your area?

I’d shoot for about 10:1, and put in a cam that makes more sense with how you’re using that car.

For a 505, something like an Icon 842 piston set up at zero deck, along with a set of 75-78cc heads puts you right in the sweet spot.

There are a bunch of variables, and the wide range of responses shows that.
Here is what I will add.
1) If you need to put close to $1000 to fix the guides, valve job, resurface, replace parts, etc. Then just buy aluminum heads. You will tolerate more CR & make more power.
2) Your combo has several things that should help tolerate CR, but still your experience shows your current CR is too much. The timing curve change can help, but may not be the only thing needed. If you could reliably control the timing curve to come in much later (3000 rpm?) it stands a better chance.
3) That 68cc chamber is a problem. 10.0 CR should work with 93 octane, and no need to push it over 10.5 with iron heads. IMO

Call Todd at Marsh Performance and buy a set of aluminum heads from him. They are reasonable and you should be able to keep the compression you have or close to it. He will steer you right and know what you can get away with.

I agree with you Jim my current heads need to much money to repair. i just have to pull the trigger and order a set of heads which i should have done years a go,

Buy the best you can afford, not the cheapest ones
get the big ones

One reason aluminum heads are less knock sensitive: less power.

EDIT; I agree on contacting Todd Marsh. He may be able to add a bit of chamber volume as well if required to get the right combo.

11.5 and open chamber iron heads will never work with pump gas; especially with contaminates in the chamber. I don't go any further than 9.5, with quench pistons, in open chamber iron heads and pump gas; but I do use shorter cams. I use 84cc alum heads with 9.8 pistons in one of my drivers with 93 octane pump gas and have zero issues. I really like this combo, but I don't chase every last horsepower either. my thoughts on the 9.8 engine was to allow for some carbon build up which should put me well over 10:1. there are many factors to building in detonation resistance (no such thing as detonation proof) into an engine.