mls gasket compression change

[1fast97gsx]

how much will installing an MLS headgasket lower compression assuming no milling has been done on the head or block? My block has been milled, as well as the head, however I just want to get an idea of how much of a compression change I am looking at in worst case scenario ( meaning nothing has been decked at all )

 

[slim2005]

Bump*** I would like to know the answer to this

 

[fwdmaster]

it will stay the same

 

[TOONAH]

You need to know how many thousandths were removed from the head and the block deck and subtract/add the difference from the gasket thickness. As the man said the difference usually has little effect on compression, but can make a serious difference to your valve to piston clearance. If more than 0.010" were removed from the head and 0.010" were removed from the block, you subtract 0.020"
from the required 0.051" and you probably will bend a valve at 7000 rpm with stock valve springs due to the phenomena known as "valve float". Standard MLS gaskets are actually 0.051"
compressed so the valve to piston clearance is maintained even with 0.020" removed.

 

[delta448]

To find compression ratio change:

1) find the displacement of a cylinder (pi*r^2*stroke) [ex: assuming 2L stock bore and stroke in cm; 3.1415 * 4.25^2 * 8.8 = 499cc]

2) find the volume above the piston at TDC by dividing the compression ratio into the cylinder volume [ex: for 8.5:1 advertised CR pistons; 499/8.5 = 58.7cc above the piston at TDC]

3) find the net volume of the change in deck milling + cylinder head milling + difference in headgasket thickness
[ex: a. (-0.5mm deck) + (-0.5mm head) + (-0.25mm thinner headgasket thickness from stock) = -1.25mm
b. find volume of change: -0.125cm * pi * 4.25^2 = -7cc]

4) add the volume change above the piston at TDC to the original volume above the piston at TDC [ex: 58.7 - 7 = 51.7cc]

5) divide the cylinder volume by the new volume above the piston at TDC [ex: 499/51.7 = 9.65, so in my example, you would now have 9.65:1 CR]

 

[viprez586]

it will stay the same

Sorry but this is incorrect.
Delta posted the formula to figure out exactly what you CR will be.

Changing the gasket thickness changes the block to cylinder head distance -which changes your CR.
This is like the honda guys running a block guard to raise their CR, except its a tad bit bigger. Oh did i mention they suck too?