Bolt pattern is the same. The 4V header will bolt up to a 2V Head. It can even seal the .01" raised port location, from stock. Those are not the issue.
The 4V is wider on the right side of the port. The right side exhaust port wall (as you face the head, in the pics) is offset (widened) on a 4V head. Look at it, in relation to the upper header bolt(s).
A "4V header gasket" would make contact (seal) with the 4V header, in that right side area, but the "4V header gasket" would not make contact (seal) with the 2V head surface since the 2V head surface is offset to the left. (in comparison to a 4V head)
A "2V header gasket" would make contact (seal) with the 2V head, in the right side area, but the "2V gasket" would not make contact (seal) with the header, since the 4V header "right side sealing surface" is not offset left.
With either gasket, 2V or 4V, you would not get a compression seal on the right side of each exhaust port. Bolt them up and they'll look good since the header flange will cover this up (from view) but underneath you will not be compressing the header gasket (between two matched metal surfaces) in this area. Incomplete circumferential-peripheral compression around the port. No seal.
...here's a edited image to show the widened gasket sealing surface on the aftermarket TFS Head. (for future reference) These TFS Heads (and maybe other aftermarket heads) can accommodate either 2v or 4v header gaskets. This TFS head is a 2V head with the sealing surface width of a 4V.
The 4V is wider on the right side of the port. The right side exhaust port wall (as you face the head, in the pics) is offset (widened) on a 4V head. Look at it, in relation to the upper header bolt(s).
A "4V header gasket" would make contact (seal) with the 4V header, in that right side area, but the "4V header gasket" would not make contact (seal) with the 2V head surface since the 2V head surface is offset to the left. (in comparison to a 4V head)
A "2V header gasket" would make contact (seal) with the 2V head, in the right side area, but the "2V gasket" would not make contact (seal) with the header, since the 4V header "right side sealing surface" is not offset left.
With either gasket, 2V or 4V, you would not get a compression seal on the right side of each exhaust port. Bolt them up and they'll look good since the header flange will cover this up (from view) but underneath you will not be compressing the header gasket (between two matched metal surfaces) in this area. Incomplete circumferential-peripheral compression around the port. No seal.
...here's a edited image to show the widened gasket sealing surface on the aftermarket TFS Head. (for future reference) These TFS Heads (and maybe other aftermarket heads) can accommodate either 2v or 4v header gaskets. This TFS head is a 2V head with the sealing surface width of a 4V.
Last edited by a moderator: