 |
|
|
1985-1998 [Subscribe to Daily Digest] |
I notice no better fuel consumption on premium than regular in my '91 9kt with stage II ECU upgrade. The ECU (electronic control unit) that controls boost from your turbocharger will adjust boost according to the fuel's resistance to knocking. Detection occurs at the spark plug electrode. So if you use a lower octane fuel, knocking will occur more easily, and the ECU will reduce the boost. But this only occurs when you're accelerating hard, so I don't see how it could possibly make a difference with normal everyday driving. After all, high octane fuel doesn't contain more energy - it's just more resistant to knocking.
The minimum octane rating for your car depends entirely on where the base boost is set. That's the minimum boost that the ECU can dial down to, when your right foot is calling for maximum boost. Typically, it's around 6 psi, and even if the Aero has a base boost up around 8 psi, it should be fine with 89 octane, and probably even with 87. I've always run 89 octane or higher, just to take advantage of the greater amount of boost that's possible.
Car Talk is good for comedy, but when I listen to it with friends, we get the impression that they miss a lot of opportunities for providing good advice. Their advice about high octane fuel and high performance engines is meant specifically, I would think, for non-turbocharged engines, in which the high performance is achieved by having a high compression ratio. These engines are prone to knocking with low-octane gasoline, and the only anti-knock mechanism they have at their disposal is spark retard, which doesn't provide you with a lot of leeway. So you have to use high-octane fuel to protect the engine in that case. Turbocharged Saab engines are low compression ratio, and they only knock with low-octane fuels under high boost conditions, but the ECU can compensate for that and prevent knock before it even happens.
Sorry for the long post.
posted by 70.226.139...
, Mon, 9 Apr 2007 08:20:00
, Sun, 8 Apr 2007 11:50:01, Sun, 8 Apr 2007 12:43:35
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
