Date: Tue, 01 Feb 2005 04:21:53 GMT From: Valued Customer <nonospaml.com> Subject: Re: Saab newbie
Yes, a turbo charger is indeed a compressor... However, I still fail to see the logic in lower octane at altitude is okay for naturally aspirated engines but not for turbo charged ones (suggested by Zon and I guess now Graham). Octane is a measurement of how high the ignition point of gasoline is... nothing more. Altitude is not an "excuse" to use lower octane. I'm not a refiner but I doubt octane is directly related to the cost of refining the oil. Because of the altitude, the air pressure is lower and therefore things heat up at a lower temp -- where I live at 6,200' water boils at 209 deg F and hence gasoline ignites at a lower temp too -- which leads to the 85 - 91 ratings. Turbos are actually more an asset at high altitude than sea level... and this is mutually exclusive of octane level. For example, why do you think commuter aircraft are turbo charged? Because they do make already thin air denser for combustion... but again, it is a stretch of deductive reasoning to say because things get hotter at lower pressures that octane is therefore a derivative pressure. On Tue, 01 Feb 2005 03:22:59 +0000, Pooh Bear <rabbitsfriendsandrelationsnospamail.com> wrote: > >MH wrote: > >> > > The excuse is that octane requirement is lower, >> > > because of less dense air. And that is true, for normally >> > > aspirated engines. Unfortunately, it does not apply to turbos, >> >> > Why wouldn't it apply to turbos? >> >> Turbos make their own air denser... > >Yup - would depend on the turbo control as in whether it's relative to >atmospheric presssure or an absolute figure in bars. > > >Graham
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