Originally Posted by 001mustang
Thanks 2 all.
I plan to fabricate a DIY header flange gasket from 1/4" Aluminium bar stock.
I bronze welded a layer of bronze on the primary tube mating surfaces then flat board sanded the bronze down to 180 grit.
I wonder if I should use paper gaskets or no gaskets on both sides of the DIY 1/4" Aluminium gasket?
My inclination would be that this will need to flange to transition shapes from the port to the header. Don't loose the sense that in 1/4 to 3/8s of an inch, this is still pretty abrupt.
It is acceptable to have header openings larger than the port's or at least not hanging any of it into the port, the converse is not acceptable. But a matched transition would be best. The flow of gases and to some extent liquids can be strange at transitions. When encountering a blunt obstruction the flow has to move out of the way and the resulting turbulance makes the area of the port act a lot smaller than it is. The transition to a larger area creates a thing call "vena-contracta" where the flow forms itself into a venturi that reduces the appartent area of the port. Neither is good, but the head on blunt is worse than the expansion. In practical terms , the expansion over the edge of a smaller port into a larger header tube offers a backward restriction to returning pressure pulses. This dampens their effect on reverse pumping of exhaust into the intake during overlap at low RPMs, but probably isn't worth the effort of figuring out except on a competitive racer.
I'd gasket both sides with an aluminum or copper gasket. Most aluminum plate you'll find for the adapter plate will be T6 hardness which is to hard to really bed parts into as a gasket. Gasket material, even Al or Cu is dead soft and thin so it will conform to surface irregularities, where the plate won't.