The thick and thin of it!

[Bruceynz]

Hi Guys,

I finally bought myself a dial gauge imperial vernier, just makes it easier to have a dedicated metric and imperial one, most people here think I am a nutter for using imperial but hey it is what it is and the stuff I play with is imperial.

Anyway to my post, I measured a stock bulk felpro gasket today, the one that comes in every rebuild kit, the thing is like toast! It measures 60 thou on the ring and 57 thou on the rest of the gasket. For this engine build I have bought 39 thou felpros, I did have some Mr Gasket 28 thou but sold them, just seems there was a 50/50 chance you could have water leaks with them.

Anyway those toast felpro's must be compression killers!

 

[kkritsilas]

Head gaskets can be used to add in or remove compression (small amounts). Using thin gaskets, you can increase compression (what most people want) or reduce it (sometimes also desirable, to run high compression/closed chamber heads on today's gasoline swill). Both have their place, just depends on what you want to do with your compression ratio.

 

[BudW]

I have always had good luck with Fel-Pro gaskets in the past.

A “sticky wicket” (if one wants to use that term) on head gaskets is the “installed thickness”.
Sometimes that data is published and sometimes not.

Almost any engine builder will want to know what the “installed thickness” will be - for that will affect the engine compression ratio.

On Chrysler big blocks, you can almost get any cylinder head gasket thickness you might want – between 0.027” to 0.140” (which the last one is one thick gasket).

The big block Fel-Pro head gasket “installed thickness” is 0.039”.
I would “assume” small block would be the same thickness – but not researched that, to know for sure.

If you are calculation accurate compression ratios – you need that information, as well as what the inside diameter of the head gasket is.

Also, head gasket thicknesses is one area that can be used if machining mishaps occur (or other problems come up).

- - -
FYI, on one of my big block builds, I will be using a brand name “Cometic” head gasket, that is 0.051” thick (installed) and has a bore diameter of 4.380”.
That calculates to 0.757947 cubic inch / 12.4205 cc of volume.

In this case, my total volume is 1,060.92 cc (per cylinder)
Displacement volume (bore x stroke) is 949.08 cc (7,592 cc or 461 ci)
Compressed volume is 111.84 cc
In this case, the head gasket volume is more than 1/10th of my compressed volume.

My many calculations give me a theoretical compression ratio of 9.486052 to 1 ratio.
I still need to measure the items – to confirm before I assemble the engine.
My goal was to achieve 9.5 to 1 ratio (but is close enough for me).
BudW