shevy not heme, some yrs. chevy. put a heat riser in the right side only of their V8 so when the motor was cold the heat riser would close and force the right manifold exhaust through the intake to the left exhaust manifold and out of the tail pipe. this was to help, heat up the cold gas and get the choke off quicker, when the heat riser opened, then the exhaust would get out of both sides and i guess some exhaust would still cross over, but nut much. if you have headers or no heat riser i wouldn't worry bout it.