Acid porting is usually used to cover up grinding and real porting work done with carbide bits It makes the cast iron look like porous cast iron again
Cheating
'63 Dodge 330 11.19 @ 121 mph Pump gas, n/a, through the mufflers on street tires with 3.54's. 3,600 lbs. 10.01 @ 133mph with a 250 shot of nitrous an a splash of race gas. 1.36 60 ft. 3,700 lbs.
It makes the cast iron look like porous cast iron again 
