Re: 5ktq Fuel Economy

[Wallace White <wallace@remdesign.com>]

"Wm. Josiah Erikson" wrote:
> 
> Nope : )
> Higher octane gas has LESS power per gallon. It just burns slower, so you
> don't get the preignition knock (well, I guess I should say that it is less
> suceptible to spontaneous ignition under pressure). 

That's right, except ISTR that pressure actually reduces the likelihood
of a mixture to detonate. The increase in temperature does increase the
likelihood of detonation, and that is a greater effect. At any rate,
higher octane fuels do not have more energy or anything like that.

- Wallace
  '87 5kcstq 152k

>                                                      If your knock sensor is
> constantly backing off the ignition timing because you're running too low
> octane, I guess I could see that you might get better gas mileage by running
> higher octane. In my Rabbit, for example, which has a 10.5:1 motor in it, I
> get better gas mileage and more power out of 91 than 87 (in fact, it really
> doesn't like to run on 87- complains a lot. I have no knock sensor on it).
> But in my QSW, I get better gas mileage from 87 (8.5:1 JT motor)
>     HTH!
>     -Josiah