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, Fri, 22 Oct 2004 13:54:59
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Somebody correct me if I'm wrong, but from what I understand, the Saab engine management will do three things to control pinging, pre-detonation, or whatever you want to call it, in cases when you use lower octane fuel:
1. reduce boost pressure to reduce the overall volatility within the cylinder
2. retard timing to closer to TDC, and
3. INCREASE fuel load/usage per injection sequence in an attempt to help lower the internal temperatures to reduce the overall volatility through heat absorption.
I'm an engineer not a chemist, but from what I understand, octane content (real or through additives like lead), is the main contributor to the relative volitility level of the fuel you use. Decreasing the octane level because you're "frugal" will directly increase the volitility of the atmosphere within your engine which will directly cause the above three situations. All three of the situations cause a loss of power, and the third will cause your fuel usage to increase. So you're actually "burning" more gas to get less power. Because of that you're creating much greater levels of unburned hydrocarbons so you're poluting more, working your cat harder, and decreasing your fuel economy. In addition, you're also relying upon built-in safety systems (that can potentially fail) to prevent your engine from destroying itself through pre-detonation--all because you're too cheap to use the recommended fuel. It's a severe example of being penny wise and dollar foolish.
posted by 67.10.24...
, Fri, 22 Oct 2004 13:54:59
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