Getting ready to install the heads on my 440 and looking for advice here is the build
2355 flat top pistons .015 deck clearance
915 big valve ported heads 75cc chambers
284 484 68 degree overlap purple cam installed @ 108

With a .039 gasket it comes to 10.6
With a .051 it's 10.4
With a .060 it's 10.17

For what I'm reading the only chance of quench will be with the .039 head gasket,and that lowering the compression with the thicker gasket may make it ping more by losing the quench,I want to be able to run 93 ultra without cranking back the timing a bunch. I went with the original 484 to kill some cylinder pressure. Is this combo gonna be a problem to keep from pinging?
Looking for some thoughts and experience on this

Thanks

Duane

I'd want a bit tighter quench & take some CC's out of the heads. HG thicknesses can vary a fair amt from the published specs. 10's seems a bit high for iron heads/marginal (mike the gaskets) quench. As you mentioned you do not wanna have to compromise the curve. One of our left coast members went thru a nightmare with that (SCR too high)

I'd try the 0.039" gaskets, but run a 160-degree thermostat and anything to lower the air inlet temperature like a hood scoop, phenolic carb spacer and such. Compressing the air/fuel mixture increases its temperature, so anything to lower the inlet temps will help reduce pre-ignition.
You could also switch to E-85, 105 octane and dumping in 25% more fuel helps cool things down.

Hood scoops are not an option, it is in a 69 charger I am restoring, 160 thermostat is fine, but in NJ E85 stations are few and far between. Really don't want to have to add octane booster, plus I don't really know how well the stuff works, I wouldn't have a problem knocking the timing back 2 or 4 degrees. But what I don't want is to mix race fuel, and then get stuck somewhere having to get gas and worry about it because I don't have 5 gallons of Sunoco puprple to add. Thats why I am looking for advice if I should just put the .060 head gaskets in and run 10.2 with the 93 octane fuel, or if running the .039 gasket with the quench is gonna give me better shot at not having detonation than trying to knock it down some.

With the thinner gasket you would have .054" quench... not enough to help much. Also compression too high for pump gas/iron heads IMO.

It is a lot easier to fix now vs later. Best I think is to remove some material from the pistons to lower CR to higher 9's (contact manufacturer for feasibility) or change the pistons to a small D dish. A really thick gasket (head saver copper shim?) to lower compression under 9.5 would be a non-quench alternative.

Have you verified those heads are actually 75cc?

Even with the .039 head gaskets you are too far at .54 for good quench. Your choice would be to up the compression a little and get quench by using a .020 steel shim head gasket, or stepping to as thick of a gasket as you need to knock compression down.

I would sooner go with the higher CR and try to limp it through. I'd even do an alcohol injection system if I had to.

I agree, I'd consider actually taking another .015" off the deck. It will bring the compression up to 11:1'ish, but with the tighter quench will give you a better chance at pump gas...

I ran a small block at .030" quench at 12.2:1 on pump. Get the 440 up around .040" quench and 11:1 with that much cam and you'll be ok.

Worse case you have to take a couple of degree's of timing out of it.

Green horn input here, but if his quench is good, doesnt dynamic compression ratio have more to do with detonation than static?

It would be easier to just use Cometic .027 gaskets but I don't think he would get away with 11:1 Iron heads on 93.

To the OP--do you know your cam's intake closing degree BTDC?

Engine loading and RPM plays a part in the equation too. If you have a high stall converter, it will help.
You can get some pretty thick head gaskets from SCE or Cometic, but they are $300-$400 a pair!

Quench is not good, dynamic CR still high because cam is sort of small for the static compression ratio, Stock iron heads and spark plug location at edge of chamber doesn't help either.

If it were me, I would zero deck the block for quench and toss some RPM heads on it, but I think he wants to use the iron heads? It sounds like he has some time and $$$ into them?

Only in the sense that good quench will let your engine tolerate more SCR and DCR. Either way, OP is going to be on the razor's edge for pump gas.

Sorry to tell you this, but it is highly unlikely what you have now will work at your elevation. I've done the 915 head in the 10s for CR and there is no quench/phenolic spacer/cold thermostat/cold plug, cold manifold /slow curve/loose converter/tall gear that will fix the problem.

I had a friend in your situation just have a portion his 2355s milled with a step to reduce the CR but kept the quench. Ran pretty good.

If you want to try one of the options listed, the 0.060" gasket will be your best shot at getting it to work. You will not get better results by increasing the CR hoping the quench thing will help. You lose ground faster with the increased CR than help from the quench. Again, this is from experience.

I'm running a 416 at 10.4 compression with a .039
compressed HG... this is iron W-2 heads... the cam
is what counts... I'm running a 260/270 on a 105 LSA
installed at 105.. I run it on the street on 87 octane
with NO/NONE spark ping.. thats with a 180 stat... I am
sure that with 10.6 on 93 octane you wont have a issue IF
you have the right cam... my engine made 590hp on 93 octane
with 40 degrees of timing on the dyno.. I run it at
38 degrees all the time on the street.. and will at the
track
EDIT
My pistons are at zero deck... but I have a 22cc dish
to give the compression.. if your pistons come up with
that compression at zero deck I really dont think you
will have any issue... I always try to get .040 quench

Smallest chamber possible (for your valve size) + D-dish pistons with a zero deck would be the way to go IMO.

Aluminum heads solves this

Thanks for all the input, yes, I want to use the 915 heads because I have some money into them and Im not looking to spend more on aluminum heads. my option may be to put the .060 gasket on it, mix it with some Sunoco purple, and figure out what octane booster works and keep some in the trunk in case I get stuck getting gas somewhere without the ability to mix my fuel. and yes, the heads were cc'd, that's how I know they are 75cc chambers. I was hoping with the 484 cam with 68 degrees overlap it would kill some of the cylinder pressure.

Duane

Quench will help. I feel even 10.2 is too much for pump. Especially with no quench. Use the .028 gasket and dish the piston if possible. Otherwise it's going to need good fuel.
Doug

Change the cam to something with a later intake closing point to reduce the dynamic cr.
I also like the idea of milling off a portion on the piston to create a "step head" shape.

Using the Wallace dynamic compression calculator, at 10.2:1 cr, and the cam installed at 106, your dynamic cr would be 7.78:1. That's within the pump gas compatibility range if you have decent quench.
The step head piston/get some quench idea is making good sense.