Cometic head gaskets

[preaction]

What could become an issue using a .070 thick Cometic head gaskets on a street driven Fe motor rebuilt to strict factory original specs ?

[frnkeore]

That's way to thick, unless you build it with the pistons extending, at least .020 out of the hole.

[My427stang]

I assume you are trying to make up for a significantly cut block?  Is that the plan?

No real downside as long as you watch quench like Frank pointed out.   

10.170 factory deck with .040 gaskets would be 10.210 total, so with a .070 gasket, the dimensions would be the same with a 10.140 deck.  Which is doable, I probably wouldn't want an engine cut much more.

[blykins]

I used a .070" Cometic on the last Tunnel Port build I did, just because the block came in with a deck height of 10.135".   I don't like trying to manipulate the tubes in the intake, so I let the pistons hang out of the block ~.020" and then used a .070" gasket.  We used a heavier dome piston, so I wanted a little more piston/head than the normal .038-.040". 

Unless you're doing something like that, you need to aim for a total quench distance of around .040".   In your case, the pistons may very well be in the hole and a .070" gasket will be a no-no.   If you're trying to knock compression ratio down with a thick gasket, that will cause more problems than it will solve.

[preaction]

Thanks for the responses The block has been cut to an unknown amount unfortunately I didnt believe .070 was an issue in its self but lost track of quench.

[JimNolan]

I built a stock 390 FE engine for my 57 Fairlane. The resurfacing of the block will take about .005"-.007" off the deck height. I ended up using Edelbrock head gaskets that advertised .032" thickness when in fact it was .050" thick. I ended up with a quench of .070" total. The DCR of that engine came out to 7.85DCR. It allowed me to use 87 octane gas and the engine run's fine. I'm happy with it. Myself, I wish I'd gone to a bigger cam and achieved the same thing with a .040" quench.