What are the downsides to using a thick head gasket. Long story short, I needed to replace my pistons. I have 64cc Indy SR heads on a 500" B block and want to get my compression down to 10:1. The piston manufacturers are saying with a 1009 fel pro, there is no way to get the compression down that low and retain strength in the piston itself. So the question is about going to a thicker head gasket. Are there any significant downsides?

I would call a different piston maker to see if they can make you a reverse dome piston to get the compression ratio you want in your motor
I have used them, reverse dome pistons, many times to get the compression ratio where I wanted it with 400 blocks and 4.300 stroke
As far as thicker head gaskets, I have used .080 copper head gaskets in the past to make the compression ratio the customer wanted instead of buying new pistons
If your motor has decent quench now with a .047 thick head gasket and you switch to a bigger bore and thicker head gasket you will probably loose any quench you have now

That 1009 probably overhangs the bore anyway. Not good.

My 493 came in at 8.97:1 with IIRC a 34cc reverse dome Ross piston OOTB RPM's and a .039" gasket.

I had to use the regular FelPro gasket as the 1009 overhung the bore because of the chamfer at the top. At the time it was the only other .039 gasket I could get that had an acceptable bore size.

Kevin

Call Cometic

I use a .052" thick Felpro. Don't know what .013" difference will buy you.

Cometics are MLS and require a special deck finish.

I've often wondered if there would be any harm in stacking 2 or 3 stock .019" gaskets !! I could use the extra room in the quench area.

Inefficient.



Pouring Octane Boost or Av Gas to it is a better, cheaper, and less headache than replacing head gaskets.

Beyond my understanding, but a different cam can bleed compression off.

You said "long story short", but why do you need to replace pistons? What is the problem?

you will probably loose any quench you have now
X2

a different cam can bleed compression off at cranking speed. The effect decays as RPM rises, and it's completely gone when you get to your torque curve.

I think it would be helpful if we knew what the current cr and gasket thickness is. We're just assuming its a 1009 gasket and a .045 quench.

The cylinder walls ended up getting scored pretty bad. They were able to sonic check the block and save it with a bore job. I had 13.5:1's in it, but wanted to step it down to use pump gas with some nitrous every once in a while.

Just for grins and giggles what are you calling think?? Also FWIW why do you think you need to be at 10-1 for pump gas?

I have .120 thick Cometic gaskets in my small block. Had to do it for expediency and cost. Domed pistons with a small chamber W5 just didn't work. Any way, it made intake sealing a challenge but other than that it runs fine with no issues.

I think you are talking to the wrong piston people. Ross made me some 4.500" bore pistons with a 55cc dish, strong enough to throw some boost at them.

Here's another idea...E85. Your engine would be perfect for running the stuff.

With correct squish and aluminum heads you should be able to run more than 10.0:1.
500 inch V8 has 1025cc swept volume.
13.5:1 has 82cc above piston
12.5:1 has 89cc above piston
12.0:1 has 93cc above piston
11.5:1 has 98cc above piston
10.5:1 has 108cc above piston

With correct squish and engine optimized I'd shoot for 11.5:1 on pump gas. You probably have a pretty big cam in the motor and that might allow even higher. you're only looking at 11cc from 13.5 to 12.0.

Any good piston manufacturer should be able to come up with a piston that fills the bill. Or if they don't have a forgoing blank that could be machined to work, someone else does.

R.

Ok, so you are at overbore anyway:

get new pistons with some more dish than what you have,

Ask for quench pads to match your heads,

and call it good.

Run the thinnest head gasket you can get away with.

Unless these heads are open-chamber?