My son has a 1983 fox body coupe with a Dart block 347, 10.5-1 compression AFR185 heads, Ford Performance X303 Camshaft, 70mm blow through carburetor turbo, (we only run 114 race fuel only), Lenco 5 speed, 456 gears. It is a race only car, The car ran 10.4 at 129+ mph after installing the turbo. After 2 seasons the turbo went bad (shaft end play), boost level would not stay steady went from 8lb. down to 4 or 5 lbs, back to 8lb on each pass without lifting the throttle. After a fresh rebuild on the engine and replacing the turbo with the same make model and size. We now have a consistent 8lbs of boost throughout the pass but she only ran a best of 11.3 at 123+ mph. Plugs 5,6,7 and 8 are all different shades/color ( yellow insulator Glazing), We can't check plugs 1, 2, 3 or 4 at the track between runs (all new plugs). She has a slight misfire on the big end around the 1000 ft. Has anyone ever had this issue?