High altitude, and low octane

[Robert Deis]

On Wed, 30 May 2001, Brad Wilson wrote:

> They claimed that
> while this is true of carbureted(sp?) engines, it's not true for fuel
> injected engines.

Since the big reason to use high octane fuel is detonation resistance, I
don't see how that can possibly be true.  Detonation is less likely to
occur at altitude becasue the absolute pressure in the cylinder when it is
sparked is lower.  Therefore high altitude requires less octane.

The absolute pressure in the cylinder has nothing to di with FI vs
carburation, does it?  Granted I'm no carb expert, but I have a hard time
beleiving that it does.

On a turbocharged car, things are wholly different-- that absolute
pressure is dependent on the current boost level, which isn't necessarily
connected to altitude at all (depends on your control mechanism)

> (Of course, the major source of controversy here, too, is
> that we're paying more for 85 octane than others pay for 87, 

I saw it and signed it, and that's the reason.  Not sure that it was a
good thing, though..

> ObAudiRef: I always use 91 octane. =) And there are occasional stations
> around (_very_ hard to find, and _very_ expensive) that offer 93 octane fuel
> here in the "high plains".

A couple of them will go as high as 114 if you need it- but race
octane levels have race pricing.... (-:

-- 
------------------------------------------------------------------------------
  Rob Deis                  "Let the people know beforehand what the law
  MiB3347                      is and what they are to expect." 
  rdeis at io.com                              -- 18th Congress, Rec. 75