is running 91 octane on a completly stock setup safe? i ask because i have only put in high octane in my boosted vehicle's.
YES, there would be no harm in running 91. Some may tell you that it's a waste of money because the computer will not automatically advance timing(at least on the older trucks, not sure about newer dakotas or 4.7's). It would actually be SAFER to run 91 under high heat and towing situations.
Smarter computers, such as the stock computer in a Porsche will actually advance or retard timing based on readings from the knock sensors.
The lower the octane, the quicker it will detonate.
The higher the octane, the more heat and compression it can handle before detonation.
If you ran 100 octane race gas in a stock motor it may not run as well because the timing is too far retarded or the compression is too low.