Fw: [Diy_efi] The Hunt effect

Don Sauman don.sauman
Mon Oct 10 00:44:04 UTC 2005


Hi Geoff

Does this apply when Premium ULP (98 octane) in Perth is between 8 to 10 
cents per litre dearer than standard ULP (93 octane). I have 5 lt V8 VN 
that is giving a freeway mileage (kilometerage???) of 12.7 l/100 km on 
standard ULP driven hard. Do you think I would see at that rate any cost 
benefit in moving to Premium ULP.

Don

Geoff Harrison wrote:

> 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
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