Rover v8 exhaust manifolds

[dixono]

Does a 4.6 p38 header bolt onto a 4.2 rrc block? Same bolt pattern or no?

[Tony4921]

The 3.5, 3.9, 4.0, 4.2 and 4.6 have interchangeable heads. The only difference is that the early ones had 3 rows of head bolts as opposed to the later 2 row. Even still, the intake and exhaust ports are unchanged. I tried to put a set of THOR 4.6 headers (1999-2002) on a 4.0 D2, they will bolt on the head, but hit the firewall. So, yes they will bolt onto your 4.2L heads, but not sure about firewall clearance on a RRC.

[dixono]

I see. On My 4.2 exhaust manifold the down pipe is between the two middle pipes where as the p38 header down pipe comes down around the back pipe closer to the firewall. I’ll have to look under my hood and investigate