patSS/00

iTrader: (6)

Which Cometic .030 head gaskets for 3.908 bores: 3.910 or 4.060? (Head size not a problem.)

tech@WS6store

iTrader: (2)

You have to match the gasket to the cyl head chamber. If its below bore size then youd use a 3.945 felpro. Definitely dont use a 3.910 on a 3.908 there is a possibility for issue.
Otherwise with cometic use a 4.030.

patSS/00

iTrader: (6)

Thanks, yeah I thought maybe 3.910 might be too small. Problem is, for .030 thickness, Cometic only lists 4.060 as the next bore size up. Is that too big? I want .030 because that would give me .033 quench.

tech@WS6store

iTrader: (2)

We can get 4.030 x .030 but i would not recommend it. Id recommend .035 for the thinnest. Youll definitely need to know your ptd clearance exactly if youre trying to go that tight especially on pump gas.

patSS/00

iTrader: (6)

I will take your advice and go with .035. Closest I can find listed by Cometic is 4.000 x .036, can you get those?

tech@WS6store

iTrader: (2)

Do you know for sure your pistons are at 0 deck?

patSS/00

iTrader: (6)

My numbers are on paper only, block has been away getting fixed for 6 weeks but coming back shortly. New flat top pistons for that bore are all -.01 height compared to original OEM, original size is no longer made, the only way you can get original stock height is to go to forged pistons, which all are like +4cc volume due to valve cutouts. Anyway on mine the pistons come out to -.003 deck on paper, but I will definitely measure it.

tech@WS6store

iTrader: (2)

Do not order gaskets before you actually measure. Period.
On paper is always just that. And there are plenty of pistons with near stock ch some below and some above. But get your engine assembled first.
Ive done way too many of these to trust on paper.

Case in point, i recently did a 427 6.0 for a friend. It was supposed to be .010 in the hole on paper but i was going to mock up assemble, check ptd, then mill deck. It turns out they were exactly 0 deck.

ALWAYS measure.

patSS/00

iTrader: (6)

Got my block back from being bored .010 and fitted with new pistons, and have measured pistons vs deck as -.003 which agrees with what I calculated. So now planning on ordering Cometic 4.000 x .036 gaskets. Just want to check if this is the best size available for the actual bore size of 3.908, and thickness less than .039. According to the Cometic online catalog it is, but I've seen lots of online catalogs that are out of data or otherwise wrong.

tech@WS6store

iTrader: (2)

A negative piston to deck clearance is above deck. And you can pretty much guess youll have more than that when it warms up. Meaning the piston will be even closer to the head.
I really would not recommend going that thin on the gasket though.

patSS/00

iTrader: (6)

OK I thought negative meant below deck. It's below deck by .003.