Date: Tue, 1 Feb 2005 20:25:13 +0100 From: "MH" <nomailnospamere.no> Subject: Re: Saab newbie
> > ... octane requirement is lower, > > because of less dense air. And that is true, for normally > > aspirated engines. Unfortunately, it does not apply to turbos, This sentence is ambiguous, but I read it as; lower octane requirement does not apply to turbos, and I consider that a correct statement; a turbo makes a high fuel/air mix pressure and consequently high RON to prevent engine knock. > I think you failed elementary physics... Be careful now.... > ... But when a gas is compressed, any gas, > it gets colder by nature... not hotter! No it doesn't.... What do you think the intercooler is for? When a gas expands, it cools. That's causing the puff of mist you see when you open a bottle of a carbonated drink; the carbon dioxide in the bottle is under pressure and it when it expands to atmospheric pressure, it draws heat from the surrounding air, cooling it down locally, so moisture from the air condensates in a puff of mist. The same thing happens when you open the valve on a butane or LPG tank; the liquid gas expands, drawing so much heat from its surroundings that ice will form on the valve. To prevent knock when the turbo comes on, the compression ratio in a turbocharged engine is only 1:8 or so (vs. 1:10+ in a NA engine) . The higher the MON/RON the higher the APC computer will allow the turbo pressure to be. -- MH '72 97 '77 96 '78 95 '79 96 '87 900T8 http://go.to/saab96
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