Headgasket compression

[syrushcw]

How does a multilayer headgasket lower compression? If I'm running 8.5:1 pistons with a 3 layer head gasket what will my compression be like? Is there some sort of headgasket compression formula? because everything comes down to math.

 

[dsmpat95]

they are slightly thicker than an oem headgasket. I dont know the formula. It comes down to the thickness of your muiti layered headgasket.

 

[kahl23]

If you're running an OEM Mitsu MLS gasket it shouldn't effect your compression at all. It isn't the fact that there are multiple layers but rather the overall thickness of the gasket that effects compression. I don't know about Cometic, but I do know that HKS offers two different thicknesses, a 1.2mm and a 1.6mm, obviously the thicker one lowers compression. What gasket are you using?

 

[syrushcw]

cometic

 

[kahl23]

Sport Compact Gaskets

Apparently Cometic gaskets are .051" or just under 1.3mm. My guess would be it has a very minimal effect on compression, if any at all, especially if you have had your head and block decked (as you should have if you're running an MLS gasket). I wouldn't worry about it.

 

[tnl]

i know this is a stupid question but didnt find much about it. what does it mean to get your head and block decked? do you have a link to another forum or can you explain realy quick. thanks

 

[talonDSMerr]

It's a process where the mating surfaces of the block and/or head are machined to make them flat and better sealing.

 

[jrohner]

When you get it decked, you will probably end up with the same compression with a slightly thicker headgasket. You would need to find out how much was taken off both the head and block and then you would be able to estimate.

 

[e85_4g63]

Basicly what talonDSMerr said. A machine shop will take a very very small amount of material off the top of the block of the engine and bottom of the cylinder head to create a smooth surface for the new gasket to bond "seal" with.

 

[DSM_ThuNDeR]

cometic

I have really BAD experiences with that one, I would just go with Mitsu OEM stock 4g63 gasket. I bought one, shaved the head and block, DID NOT SEAL. So. I bought another one, this time I sprayed copper spray and STILL did not seal, Oil and coolant were in MIX. Just buy oem STOCK gasket. Would save you the hassle of taking everything back off again and again.

 

[Team Addiction]

I have really BAD experiences with that one, I would just go with Mitsu OEM stock 4g63 gasket. I bought one, shaved the head and block, DID NOT SEAL. So. I bought another one, this time I sprayed copper spray and STILL did not seal, Oil and coolant were in MIX. Just buy oem STOCK gasket. Would save you the hassle of taking everything back off again and again.

Tons of ppl use Cometic religiously Im thinking this may be an isolated incident

 

[duwackerTSi69]

When you get a Cometic gasket, you have to have the head/block machined to except the new head gasket.. It has to be smooth as glass to seal perfect?? When you use the genuine mitsubishi gasket, you dont have to really prep the deck surfaces to accept theat type of gasket, all tho its ###### a good idea..

 

[TunaTalon]

The formula for compression ratio (CR) is:

CR = DisplacementVolume/HeadVolume.
The formula for displacement is:
Pi * (bore/2)^2 * stroke

With stock bore (85 mm) and stroke (88 mm) displacement can be calculated as:
(3.1416 * 42.5^2 * 88)/1000 = 499.3cc
The division by 1000 is to get the answer in cc units from mm units of bore and stroke.

If the compression ratio is known (such as 8.5:1) with a reference head gasket then the head volume can be calculated as:
HeadVolume = DisplacementVolume/CR

Stock HeadVolume = 499.3/8.5 = 58.7 cc

The additional head volume added by a thicker gasket can be calculated with the same formula for a cylinder volume used for displacement. To make it easier the head volume added for each .004 inch additional head gasket thickness ( or decreased for each .004 of decking) is:

1 inch = 25.4 mm or 0.004 inch = 0.1mm

Additional volume for each .004 inches of gasket:

(3.1416 * 42.5^2 * 0.1)/1000 = .567cc


Adding the .004 to the head gasket the new CR is:
499.3/( 58.7 + .567) = 8.424

Not that much difference.

Using the formula above you can calculate the effect on CR of any combination of gasket and decking for any bore and stroke.

 

[tnl]

wells thanks for not jumping on my case for asking something stupid i just never refered to it as decking. but the qeustion lead to some other useful info so worked out. thanks