True Confessions - Premium Gas

[denverpete]

Originally Posted by MNBoxster

You may not have a problem driving an empty Car though the Nebraska Flatlands on a 30° Day at 50MPH with the CC on, but load up the Car with Passenger, Luggage, full Fuel Tank, or drive Up the Rockies or through the Desert at 120°F, and you could create serious problems. Ambient Temperature, Altitude, and Load are major contributors to Knock. Ever notice when you hear an old Car knocking it's usually accelerating or going uphill?

Happy Motoring!... Jim'99

I agree that temperature, altitude, and load are contributors to knock. But that old car knocking is generally because that vehicle doesn't have the modern computers capable of adjusting the spark timing and air-fuel ratio.

In truth, an increase in altitude would decrease the necessary (R+M)/2 number by 1-2 per 3000' elevation. As such, octane numbers for gas in the Rocky Mountain region are lower than those in lower altitude areas (87 is considered "mid-grade" with 89 to 91 as the "premium" here). As such, wouldn't you actually be better off increasing in altitude with 87?

[MNBoxster]

Originally Posted by denverpete

I agree that temperature, altitude, and load are contributors to knock. But that old car knocking is generally because that vehicle doesn't have the modern computers capable of adjusting the spark timing and air-fuel ratio.

In truth, an increase in altitude would decrease the necessary (R+M)/2 number by 1-2 per 3000' elevation. As such, octane numbers for gas in the Rocky Mountain region are lower than those in lower altitude areas (87 is considered "mid-grade" with 89 to 91 as the "premium" here). As such, wouldn't you actually be better off increasing in altitude with 87?

Hi,

Agreed on all point. My mention of the Rockies was not in reference to the Altitiude, but to the Load imposed on the Car by going UP (I should have been more clear). I agree tha lower density raises the detonation threshold, because lower compression pressures are achieved and there is less O² to oxidise the fuel...

Happy Motoring!... Jim'99