OK got my headers CeraChrome coated by Caps in Frenso, CA... (love em) and ordered gaskets from Clifford (thought my headers were Clifford). Ran for 3 days and blew the gasket where the header meets the upper 3-1 Y. Clifford sez that I have a "short set of headers" that are not "Clifford" style because they terminate in the engine compartment and that Clifford headers terminate outside (aft)of the engine compartment. This results in a higher temp in the collector that are too close to the exhaust manifold which caused a premature failure of the gasket and I need to use a alternative gasket (copper) due to the temp difference. I spent $$$$ for those gaskets....Do I need to replace with copper vs some other material. The gaskets I removed prior to coating the headers was your typical gasket material and did not have any problems. Your thoughts?
My thought is that Clifford is making a pretty fair attempt at covering their hindquarters because their gasket didn't hold up. If the old gasket you removed before coating the headers held up, I'd be real tempted to use the same kind of gasket again, with a bit of high-temp silicone sealer as insurance. The coating that Cap's does is supposed to REDUCE the temperature of the headers, which I've found to be true in actual operation, which in turn reduces underhood temperature as well. So what the good folks at Clifford told you sounds to me like what Buffalo refers to as "donkey dust". If you want to use a copper gasket, it'll hold up darn near forever, but they are a bit pricey. I think if I were in your place, I'd try using the same kind of gasket you originally used, and if that blows out, go with the copper one.
The Clifford supplied gasket material for the header flanges and the intake/exhaust manifold are made out of the same (white/rubberized) material. This material is also about 3 times thicker than the gaskets I removed. I soaked the new gaskets for 45 minutes in warm water prior to install as per the instructions from Clifford. The flange gaskets got very brittle after only 100-200 miles of driving. I am still getting a slight whiff of burning rubber from that gasket material. The Clifford Rep says this is the 1st that they have heard of this type of failure. One thing that may have contributed to the failure of the collector gasket is the torquing/twisting in that area from the engine movement whereas the intake/exhaust gasket is not subjected to those stresses. I think I will spend the extra $$$ for copper for added insurance.
The technical data that HPC and Jet Hot have shown for their coatings, which I believe are similar to Cap's, certainly reduce the outer surface temperature of the headers and also reduce the heat radiated to the other parts near the headers. This means that more heat energy stays in the exhaust gas and the exhaust gas will be hotter with the coated headers. I do not recall how much, but it is sometimes advertised as a benefit, as the higher temperature means higher velocities and potentially better scavenging. Could it be enough to roast a rubberized gasket? Going to copper sounds like a good idea.
The exhaust gas in the header will be in the range of 700-1000F and that is more than adequate to fry the elastomer holding the fiber gasket together. But once the elastomer has been effectively "baked out", there should be a dense enough fiber mat left to act as a seal. From this point on, the success of the gasket is the rigidity of the flanges/bolting. The fiber mat will seal if the joint isn't moving with the thermal cycles. Even seemingly negligible movement in the joint will break up the mat and result in a leak. These elastomer bonded fiber gaskets are used successfully in a lot of high temp applications, but only in well designed flanges. And sad but true, most header joints aren't stiff enough to be reliable with the fiber gaskets. Bolts undergo stress relaxation with time at temperature-loosening the joint. And the thin low carbon steel flanges have the same problem. The graphite gaskets will take the temp and are more forgiving of a weak joint-but only to a point. And thicker usually ain't better. It is just one more loosening problem as the mat looses bulk (elastomer bake-out). Check the flanges for flatness since overtightening weak flanges to make a seal can warp the flange and make an even loading on the gasket impossible. The hard copper gasket will make this especially important since it doesn't have much give. And good luck!
Were can I find a copper gasket for a 250/292?
Come on, nobody knows were to find copper Gaskets ????