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Hi All,  

With gas prices going up and away I was wondering if anyone is using the grade level of 89 gas in their Saab 95"s? Manufactor recomends 90 or above grade and but the price is extremely high. If anyone is using  something beside 90 are you having any performance trouble? New to this site so your responses are appreciated.  

Thanks
slovins  

slovins,

I own a Mazda 626 which uses primo. From what I understand, virtually any vehicle within the past decade can use lower grade fuels if the manufacture says "recommended" on higher grades. However, you'll always experience a performance hit at lower grades. My car does at higher speeds and when revving.

If you're car's "Required" to use a certain grade, you're out of luck  

These are factory recommendations made because of how your ecu is tuned. Basically if it is making the recommendation, then it was tuned for a higher grade gas so to speak.   A higher grade gas is more stable (which means it takes more heat to ignite then lower grade gas) and burns more evenly. This means that your car will see less pre-ignition and detonation because of using a better grade gas (I say less because it is impossible to eliminate all knocking).  If you use a lower grade gas, your car will see more pre ignition and detonation.  Most ecu's are programmed to retard ignition timing when they detect knocking from the pre-ignition and detonation, this helps keep your car safe from overly excessive ?detonation? but still is not good for your car.  This is where the "hit in performance" the previous poster was talking about happens.  Your car makes power based on ignition timing and the more it is decreased the more you loose power.(this is a whole separate topic).  

So you use a lower grade gas, your engine starts to ?detonate?.  Your ecu detects this and pulls out 10 degrees of ignition timing.  This happens lets say every 3 miles.  That means that every three miles your engine is receiving a counterproductive explosion that creates extremely high cylinder pressure and puts over excessive strain on your engines internals.

This is even to say that your car does retard ignition timing when it detects ?detonation?.  Some cars do not.  This would be the worst case scenario.  

Although every car will benefit from a higher grade gas, some cars need it and if the factory is making the recommendation, I would follow it..


Edit... it has been a little while since I talked (or tuned a car for that matter)about ignition timing pre/ignition and detonation.  Please feel free to tell me if I forgot something or if there is something you dont agree with.