<VV> Re: octane and alky - adjustment in a Corvair

[Eric S. Eberhard]

Our Land Cruiser actually lists different horsepower based on the Octane 
(actually based on using premium or regular).  I assume it adjusts timing 
primarily by detecting knock(?) and that the adjustment lowers power.  It 
could possibly adjust fuel as well.

On a Corvair, automatic detection is probably unlikely.  However, I have a 
friend here in AZ that uses an MSD ignition with an instrument located on 
the dash to make all kinds of adjustments with all kinds of controls.  He 
uses it to adjust for altitude (because it is easy to go plus/minus 3-4000 
feet here) and to adjust for fuel.  I believe it does more than just retard 
ignition, I believe it also affects the advance curve if desired.


At 02:26 PM 6/21/2005, FrankCB at aol.com wrote:
>Padgett,
>        I'm not sure just how this would work.  Do you mean that the engine
>would be controlled so that only with the highest octane fuel (say 99 from
>straight ethanol) would the throttle valve be able to open COMPLETELY thereby
>putting the max charge of air and fuel into the combustion chamber and 
>giving max
>combustion chamber pressure?  With lower octane fuel (say 87 from "regular"
>gas) the electronic control system would limit the opening of the throttle 
>valve
>so that it was somewhat less then 100% and the resulting chamber charge would
>be less than maximum.
>        But how does the manifold vacuum come into this setup?
>        Frank "seeking knowledge" Burkhard
>
>
>In a message dated 6/18/05 9:19:56 PM Eastern Daylight Time, pp2 at 6007.us
>writes:
>
> > GM is also moving toward true "fly by wire" with no direct connection
> > between the gas pedal and the throttle plate. With that you can control
> > chamber pressure via manifold vaccuum so you design the engine for the
> > highest octane fuel and then dial back the effective compression ratio  to
> > the current fuel. This is even easier to do with a boosted engine and a
> > waste gate. (IMNSHO there is a place for supercharging - above 20,000 
> feet.)
> >
> > This is really a far superior method than retarding the spark on 
> detonation
> > but was what the automakers had available that was cheap since with
> > traditional controls they could not control the nut behind the wheel.
> >
> > With electronic control, when the pedal hits the metal the computer can
> > control the max chamber pressure to what the fuel is capable of. Toss in
> > VVT and the engine can be kept at the peak of efficiency even on moonshine.
> >
> > Padgett
> >
>
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Eric S. Eberhard
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