Dan, before you send that header out to be coated, you need to do a few things first.
Check to be sure the thickness of the header flange where the attaching bolts run through is 12 mm thick (.472 inch). If not, the washer of the intake/exhaust bolts will not sit flat across the intake and exhaust surfaces, and it will not seal correctly.
Check to see if the flange itself is warped, or if the welded areas around the ports have any voids that would create leaks.
Check the fit of the header flange relative to the intake manifold flange you will be using....often there is interference here and it must be ground away to fit.
Check the fit of the header in the chassis itself. It is not uncommon for the header to strike the engine mount bracket, the bell housing or the bracket attached to the bell housing and block, and number 1 header tube may interfere with the underside of the intake manifold if you are using a stock down draft intake. Another possible point of contact is the frame rail itself.
If all this sounds unlikely to you Dan, it really isn't! I've tried to install GT headers that had EVERY one of these problems. But better to make your dents and grind the header now than after the header gets coated.
Another tip: The fiber type header gaskets tend to blow out easily. To help them seal better, soak them in water for about a half hour before installation. Then install the wet gasket, and torque to spec, starting at the center and working out in a three or four step process. Run the engine until the engine is up to temperature, then shut it down and let it cool off. Once cool, torque again. They will likely be very loose. The water helps the gasket to conform to irregularities. After this, the gasket will be *molded* to shape, and should seal well. Re torque after about 100 miles or so.
Bob
