Make sure that your headers have a good seal to the cylinder head by using a high quality exhaust header gasket from Cometic.
Cometic custom gaskets can accommodate virtually any engine configuration from naturally aspirated, to the most exotic and nitrous injected engines.
M-9448-A462 Race quality replacement header gaskets for 4.6L 2 valve engine.
COM-C5548-064 GM SBC 23 Degree Exhaust Gasket
COM-C5805-030 FORD 7 MUSTANG 5.4L Exhaust Gasket
COM-C5836-030 CHEVY SB2 EXHAUST-3 Exhaust Gasket
COM-C5894-030 GM SBC 1.450" Exhaust Gasket
COM-C5895-030 GM LT1 1.520" Exhaust Gasket
Cometic triple layer exhaust gasket made specifically for the Yates D3 racing cylinder head and is used on all D3 Roush Yates Racing Engines.