My VW Passat requires 91 oct or higher. I can put in lesser gas, but the engine computer will adjust the timing to prevent engine knock. The overall performance and fuel economy would go down. So, it's false economy to put in lesser gas.
1994 MB E320 Coupe (199,500 mi)
1992 MB 190E 2.6 (173,000 mi)
1983 Porsche 911SC (148,000 mi)
2004 Volvo V70 2.5T (198,000 mi)
President of CT/Westchester Section