hey y'all, i would like to know some of you guys opinions on this topic, it got me thinking and you guys have alot more experience and would have a better idea. i was havin a yarn to a guy at work about exhaust back pressure in performance cars, he reckons it helps engines run better but couldnt tell me exactly why and was stumbling with his words then started mumbling and trailing off about different rev ranges and sound pulses or whatever and mufflers making the car quieter etc which didnt help convince me its beneficial, i thought the idea was to get air in and out of an engine as quick as possible and how can back pressure from mufflers or whatever be helping get air in and out of the engine if its a restriction that holds spent exhaust gas in the exhaust system and when the exhaust valve is open the gas aint fully leaving the combustion chamber and is diluting the incoming fuel air charge, why else would people drive their car to the track then uncap the headers to race then cap them back up to go home, wouldnt they just race with the exhaust system in place?

so are there any circumstances where exhaust back pressure helps engines run better