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Re: Using lower octane in a 9-3. A problem?
Posted by MO (more from MO) on Thu, 29 Jun 2006 07:46:42
In Reply to: Using lower octane in a 9-3. A problem?, David, Thu, 29 Jun 2006 06:40:52
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21.7 highway sounds low to me. I get 29-30 highway in my '99 9-3 base model.
The reason for recommended octane levels is to prevent knocking (aka pinging or detonation), which is when the compressed fuel/air mixture in the cylinder explodes all at once instead of burning smoothly as the piston moves down. This is bad for your pistons and valves and will eventually lead to very serious engine damage. Knocking becomes more of a problem when you have higher compression in an engine, either from high compression ratios or turbocharging. Higher octane fuels are more resistant to exploding in this way, so they can withstand higher pressures.
Saabs have very advanced (maybe the world's most advanced) knock detection, and they can adjust the timing of the spark to avoid knocking. The spark is delayed until after the piston has started to travel back down and the air/fuel charge has started to decompress, so that you avoid explosion. The result, though, is that you get less power and less efficiency from each stroke.
So yes, you should get better gas mileage from the recommended octane gas. And, if Saab engineers have done their math correctly, you will not see any further improvement from higher octane (ie, if 91 is recommended, 89 will reduce your power and mileage, but 93 will not be any better than 91) because the recommended octane should be high enough to prevent knocking in your engine without retarding the spark timing.
Also, remember that if your mileage increases by only a little, it's still probably worth using the more expensive gas. The price of 89 here is less than 3% more than 87, and even 93 is only 5% more than 87. So if your gas mileage goes up to 23mpg highway, you're saving money.
If you don't get more than 23mpg highway, you either have an incredibly aggressive driving style or something else wrong with your car, so report back :)
Good luck,
Matt
'99 base
posted by 65.107.212...
Posts in this Thread:
- Using lower octane in a 9-3. A problem?, David, Thu, 29 Jun 2006 06:40:52
- Tire pressure ...., SeeVTSaab, Fri, 30 Jun 2006 04:25:02
- Re: Using lower octane in a 9-3. A problem?, Dean, Thu, 29 Jun 2006 09:04:38
- Wife uses regular in her 2001 9-3, gets better mileage, Peter_MA, Thu, 29 Jun 2006 08:45:36
- Re: Using lower octane in a 9-3. A problem?, MO, Thu, 29 Jun 2006 07:46:42 <-- Viewing This Message
- Re: Using lower octane in a 9-3. A problem?, Jeremy R., Thu, 29 Jun 2006 06:43:26
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