<VV> Re: octane and alky

[FrankCB at aol.com]

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
>