Where can I find a thicker headgasket? Fiat 2000cc

[vandor]

Hello,

I am looking for a thicker than stock headgasket for a Fiat 2000cc 8-valve engine.
I have friends who had a hard time sealing up solid copper gaskets, so I'd prefer a multy-layer gasket.
I used to know a manufacturrer herein the USA, but misplaced the info...
Any leads would be appreciated.
Thanks,

Csaba
'71 Fiat 124 Spider, much modified
'67 Fiat 850 Coupe, needs lots

[robert kenney]

Csaba.

I used a Nava Linea gasket that I purchased from Guy. It was 1.5mm thick (.060). He recomended these for all high performance T/C Fiats with a 85mm bore or less. I did run the pistons proud of the deck.020 to ensure a .040 quench band. I did use pistons to my drawings though. These did not follow the traditional T/C dome quenrch band location but a 0 degree band utilizing the combustion chamber/ bore over lap. I am happy with the performance but some may be sacrificed on top. No way to tell for sure as it will never see an engine brake.


Robert

[Guy Croft]

Some points on this because it is a frequent topic for discussion around the world.

I've just measured an early pattern 'thin' OE type head gasket of the sort used on TCs of all kinds from 1969 - introduction of the thicker Astadur type in 1995 on the 130TC and Volumex. Compressed thickness:

thin - 1.2mm
thick - 1.65mm

With an 85mm fire ring bore this gives a difference betw the two of 2.55cc.

So if say your engine had the thick gasket and you had 10/1 CR and you changed to the thin one - apart from reducing your valve - piston radial and vertical clearances and bringing the piston closer to the head face and chamber you'd increase the CR from 10/1 to 10.4/1 and vice versa. You just would not notice more 2 -3 bhp difference on dyno test from that - if that and certainly if going from an engine that originally had a thick gasket to a thin one it would not provide the least protection on a turbo conversion where you have to go form say, 9/1 to 8/1 or lower..

You have to have seen a lot of head gaskets to really understand what's 'at stake' (involved) here from a practical perspective. To get high strength in a head gasket you need a stronger fire ring. I don't mean material necessarily (because ductile iron is perfectly good for everything except turbocharged units running 30psi+ boost) but the width of the fire ring. The holding strength (to withstand the firing pressure) of a conventional head gasket of the type under discussion is NOT just about pressure=force/area - it's as much to do with the 'cold flow' of the ring across the bore and head. This is why surface finish on block and head is important- too smooth and there will be less cold flow and less frictional grip. (The converse is true: too rough and there will leakage paths all over the place - esp in the coolant regions). The wider the fire ring the more surface interaction there will be. If you want to know a bit more detail about friction read my page at: http://xpcfastener.com/page2.html

The other critical design feature is the strength of the backing (substrate) material in the gasket - a stainless core and infill material to support the fire ring and perform the other sealing functions, because of course the fire ring - which is folded over the substrate - will be ineffective if the firing pressure is strong enough to force the substrate out radially - which is exactly what happens during a detonation event. It is clear to me that production of stronger substrate materials and wider more robust fire gaskets has inevitably lead to their becoming thicker. Whether that is because the core is thicker or the infill of Astadur or other thermosetting polymers is (or has to be for production reasons) thicker I don't know but they certainly are far more surviveable than the early thinner designs with basic graphite/asbestos (or substitute composites).

I take a fairly rigid view of engine parameters. In my view (which is more informed than most let's be honest) the component that really should be used to set a 'given' engine's CR (ie: with fixed stroke, head volume) is the piston by means of diameter (ie: bore size), compression height, dome (or dish) its valve relief volume.

The photos below illustrate the key features I'm talking about.


GC