Head gasket thickness and compression ratio changes

I read somewhere that a .010 difference in head gasket thickness will increase compression ratio by .5:1. Is this true?

I just swapped out my .055 thick gaskets for .039 thick, for a difference of .016, which should equal out to a .75 increase in my compression.

Just sounds like a pretty big number considering that it is just a gasket...This would bump me up to 10.25:1 if it is true...

 

IIRC, .004" is equal to .1 compression.

If my memory is correct, then .016" would gain you .4:1 compression.


Edit:
Or was it .004" is equal to 1cc difference in chamber volume...

I am confusing myself now!


If your equation is correct, you gain .8:1 compression.

If mine is correct, you gain .4:1 compression.

If .004" is equal to 1 cc compression area, then you lose 4cc and have to figure your compression as before, but 4cc less volume.

 

I am pretty sure .004 equals 1cc difference in chamber volume.

The .041 thick gasket has 9.0 cc, the .039 has 8.5 cc according to descriptions on JEGS website.

 

Ran the numbers through my EA...
-4cc raises the compression almost .4:1.

That means both my equations came out accurate!

 

So I am gaining almost half a point with these gaskets? Closer to 9.9 or 10:1?

Now you got me confused...

 

is this .4:1 per cyl. or per gasket (divided by 4)?

......

 

You don't know what you really have unless you measure everything and calculate. Plug in the numbers:
http://www.fordmuscle.com/calculators/compression.shtml

The biggest inconsistancies are head chamber volumes and piston-to-deck heights. You have to measure.

Why on earth would you run .055" head gaskets unless your pistons were sticking .015" out of the holes?

 

He Got The Motor That Way

 

They were whatever was on there stock. I yanked them off and measured them at .055. New ones will be .039.

 

do you know if anything has been cut off the block?
maybe they decked the block or milled the heads and ran a thicker gasket to keep stock compression or as barry said...are the pistons sticking out of the block...
...and on ...nonadjustable rockers it keeps the valve adjustment correct...

...:Handshake...

 

Block is a remanufactured long block, pistons are .040 over, there is a slight chance that the block has been decked, just to true it up.

The pistons are not sticking above the deck, right even or just a little under, barely. Flat-top pistons with valve reliefs.

 

I just measured it....012 clearance between top of piston and deck.

 

This was just a stock engine, stock heads, and those were crappy mr gasket replacements, I would guess...Not the best in the way of performance...

 

I'm thinking on a jasper or such as rebuild line, they make sure they have the clearance with the thicker gasket. What thickness would be on a new stock engine?

 

So with the .055" gaskets the squish height was .067 for that cylinder.
I've seen stock engines with as little as .005" piston-to-deck height on one cylinder and .019" on another.