Guys, I have noticed that it seems like the Fel Pro 1008 is the "go-to" head gasket for small block Mopar with .039" compressed thickness, and a 4.180" bore. What is the science behind using a gasket with a bore much larger than the bore of the engine itself. I noticed that there are Cometic gaskets available with 4.040" bore, and 4.060" bore. When would a gasket with a bore closer to the cylinder bore size be ideal? Thank you for any responses, I still have a lot to learn.
Head Gasket Preference
- Thread starter D&R Const
- Start date
-
omahamoparguy
Well-Known Member
- Joined
- Feb 19, 2010
- Messages
- 756
- Reaction score
- 32
I think the larger bore would cover all possible options with room to spare. Like a 340 that someone has bored .060. or maybe an x block. Not totally ideal because of the crevice can hold combustion gases that can go unburned and this alters compression slightly. This way the manufacturer does not have to worry about having a bore on their gasket that is too small. Obviously the custom bore gaskets would be for custom builds or racing application where this kind of detail is appreciated. Still. on most applications, a 4.180 bore would not be needed. {look at the price, of the two.} so, it boils down to cost I think.
Cometic gaskets will be of the "mls" (multi layer) style gasket, with no chance of a "fire ring" issue, this fire ring is part of the make up of most common style gaskets. The fire ring if too close to the edge of a bore or more likely too close to an irregular shaped cylinder head, may not seal properly and eventually let go. Hence the larger diameter. Don't worry. You won't have a problem.
nm9stheham
Well-Known Member
My son's 4.7L V8 uses MLS gaskets as standard/stock. It may be more of a cost issue for standard production.
We used 4.125 hole Cometics on a 340 with a 4.060" bore. The 4.080" size was tempting, but any misregistration of the gasket holes vs the bore holes exceeding .010" would have left the gasket edge over the open bore.
We used 4.125 hole Cometics on a 340 with a 4.060" bore. The 4.080" size was tempting, but any misregistration of the gasket holes vs the bore holes exceeding .010" would have left the gasket edge over the open bore.
moper
Well-Known Member
All bores will have a taper on the top to allow for assembly (the rings use this as a ramp to the bore). You don't want a gasket that is exactly the same size of the bore. As said above- the gasket's edge (that's exposed to the combustion chamber temps) has to be supported fully by the block and head. That helps it transfer heat into those castings, letting it live. You are right - there's a lot of wasted volume with most common Mopar gaskets. but that's also just the way it is with aftermarket parts. They are made to "fit all xxxx".
Thanks for the responses. Do you feel that the ideal gasket bore is the same diameter as the wider part of the taper at the top of the block?
moper
Well-Known Member
That would be ideal, yes. But for the vast majority of builds, totally not worth paying for. The only engine I would use a custom gasket on would be a 273.
I like head gaskets that seal.
nm9stheham
Well-Known Member
Ideal yes, but perfect centering of the bores in each gasket hole will not be possible with every gasket on each and every block so some 'hole slop' is wise. Re-ordering head gaskets in case a too tight gasket hole does not center up perfectly on each bore is a time and $$ cost that does not buy you much, if anything.
Last edited:
famous bob
mopar misfit
USE AROUND .030 LARGER GASKET BORE SIZE FOR SAFETY. don`t want any hanging over in the cyl. after compressing (torqueing) them. will be close at that ! jmo
-
