Fw: [Diy_efi] The Hunt effect

[Geoff Harrison]

On  Tuesday, October 04, 2005 9:12 AM
DH wrote


> Took a trip to Washington a couple of weekends back.  Told my Prius 
> driving
> Texas friend (From Austin) that he should start purchasing 89 instead of 
> 87
> octane.  That's 'cause it would cost him less.  Well, partner, he said he
> would try it if I paid the bill, which I did.  We shared driving duties 
> and
> sure 'nuff the car got 51 mpg instead of the previous 48 mpg.  We did this
> averaging over 80 mph (while moving) and with two drivers.
> How does 3mpg save money?  Well that is 3mpg divided by 48mpg which is a
> whopping 6.25% improvement.  Big deal? Well yes!  You see that gas cost 10
> cents more per gallon which is 3.22% more.  Since I'm an accountant I
> noticed that the 3% increase in cost (because gas is quite expensive now)
> was giving a 6% increase in mileage.  That, folks, is a 3% reduction in 
> gas
> price per mile.
>
> Don't mean squat in a non-computer controlled car, but in engines that 
> have
> high compression (over 8.5:1) and 'bouncing' engine management (where the
> ignition is repeatedly advanced until the engine pings and retarded
> slightly) you can expect the same gains.
>
> Please, try this for yourself and report the results.  Especially those of
> you that have a consistent route to work and don't run into a lot of 
> traffic
> in-route (both of you).  Report your results here, in public.
>
> In reality, it should also work for even older engines with lower
> compression.  I first noticed the effect with an 83 Olds with computer
> controlled carburetor and that was NOT a sophisticated engine control
> system.  With that car the engine got about 6% better fuel mileage making 
> it
> breakeven even at $1.50 per gallon.  With the wonderful side effect of 
> being
> able to pull the hills of North Alabama without pinging.
>
> I call this phenomenon the Hunt Effect.
>
> dh

I became aware of this about 3 years ago. The company I worked for paid for
my fuel. They whinged because I was using Caltex Vortex (95 RON). Their 
discount scheme with Caltex was only applicable to UL (91 RON). The car is a 
common garden variety Holden / Buick 3800. 91 Model, on 8.5:1 CR. So it 
shouldn't need the extra octane. At the end of the day I won the argument. 
It was costing me less to run the vehicle on the more expensive fuel, as it 
went further on a dollar. That's the bottom line.
The fact it was costing the company more was their problem, and they should 
talk to their supplier.

The Vortex also has a cleaning agent, which may have more to do with the 
better economy. As far as I know the ECM doesn't use the "bouncing" effect. 
But I'm still leaning about that.

Can't provide current data. I would have to go back to std fuel.

Geoff