From:             "M_Gosnell@email.msn.com" <m_gosnell@email.msn.com>
To:               "Land Cruiser Mail-List" <80_series@sgiblab.sgi.com>
Subject:          Fw: [80] Timing advance
Date sent:        Tue, 4 Apr 2000 16:21:01 -0500
Send reply to:    80_series@sgiblab.sgi.com

----- Original Message -----
From: George Couyant <george_couyant@hotmail.com>

> > I've heard the question "why not use 92 octane fuel?"  The rationale I
> > read on this is that 87 and 92 fuels contain the same amount of energy,
> > just that the 92 prolongs the onset of detonation (knock) longer than 87
> > octane. The key to obtaining maximum performance with any engine is to
> > tune the engine so that CONTROLLED gas ignition occurs just prior to
> > UNcontrolled detonation or knock. This whole process
>
> Precisely. What we do for those who wish to occasionally run PULP or new
> Shell Optimax (which actually does deliver a tad more power) for towing
> etc, is to create two ignition maps on the Unichip. Optimise ignition
> advance and fuel maps on ULP on the dyno and then have the customer come
> back after a tank or two of their desired fuel and again optimise the
> 2nd ignition map for that fuel. It's then wired to a switch. Same goes
> for LPG.
>
> Cheers
> gc


Actually, in some locations, such as here in Chicago, the higher octane fuel has
less energy. In order to reduce emissions oxygenated fuels (ethanol & MTBE) are
used to increase octane. Being oxygenated, they have a lower energy content.
Sometimes people will observe reduced mileage, when higher octane fuel is used,
and not know why.

Matt