It depends on alot of varies..Compression is a big factor...I run a 572 bbc with a Holley that was modified to reach 1500 cfm on the flow bench.I can change the oil,and after a couple of runs,the oil will thin and smell of race fuel....I change it regularly...It is a sacrifice...Ya wanna go fast,Ya pay...Ya might also check the rings with a leekdown test...Good Luck!!!!! dan
Too much carb, too much fuel pressure, Bad needle and seats, worn out engine, Electrc pump left on too long?.....
...check your fuel pressure at the carbs...blowing by the needle/seat...causing the fuel to flood past the rings...next do a cylinder pressure chk...may be also getting past the rings...