Brand of Gasoline

[Cody Forbes]

Drive them both under identical conditions first to verify that they are as identical as you think they are ;-). 

-Cody Forbes

On Sep 21, 2012, at 2:29 PM, Louis-Alain Richard <5145727795 at bell.net> wrote:

> You know what ?
> 
> I'll borrow two identical cars from a Press fleet, drive them in parallel
> for 500 km, and report back the results. That way, we'll have a
> semi-scientific data point... And that'll will fit right in one of my next
> editorial for the magazine...
> 
> More to come.
> 
> Louis-Alain
> 
> 
>> -----Message d'origine-----
>> De : Grant Lenahan [mailto:glenahan at vfemail.net]
>> Envoyé : 21 septembre 2012 14:11
>> À : Cody Forbes
>> Cc : Louis-Alain Richard; <quattro at audifans.com>
>> Objet : Re: Brand of Gasoline
>> 
>> Yes, completely right. That's why i noted that there is only a finite
>> amount of advance possible.  So the idea that we'll just keep advancing
>> and get more economy is fallacious.  At high vacuum you are already at
>> optimum, likely.
>> 
>> Advance is (mostly) dealing with the elasticity of air, and the finite
>> speed of the flame front expansion, and that especially at high rpms, you
>> actually need to begin well before TDC to apply maximum expansion through
>> the majority of the power stroke. Start at TDC and the piston is well down
>> its stroke before the expansion applies much force.
>> 
>> however, do it too soon and you begin to oppose the travel of the piston -
>> reducing economy and power.
>> 
>> This in fact is what knock (aka pre-detonation) is,and why it is
>> potentially harmful.
>> 
>> Grant
>> 
>> 
>> On Sep 21, 2012, at 1:34 PM, Cody Forbes wrote:
>> 
>>> I think there may be some misinterpretation possibly. Timing advance has
>> an optimum number which you get ZERO benefits for surpassing. This is
>> easily to see on a braked Dyno (not an inertial) with a tuneable ECU. I
>> can, and have, watched torque numbers increase to a point as I advanced
>> ignition timing and then at a certain point the torque will start to go
>> back down. Typically on race gas or E85 I see peak torque in the mid RPM
>> range 2-4 degrees before I see knock. At higher RPM the spread is greater..
>> On 93 octane it depends on boost level and the engine. The 1.8t powered S3
>> race car I tune will easy run 15-18 PSI on 93 with no knock at peak
>> torque. Along with watching peak torque rise and fall you can also see EGT
>> fall until about the same as when you make peak torque then more advance
>> causes EGT to start increasing again.
>>> 
>>> I'm sure that BMW ECU tries to keep it advanced, but only to the mapped
>> optimum. Going beyond that is DECREASING efficiency. If its running on a
>> lower grade fuel than required sure it'll keep increasing as much as it
>> can, but on the proper grade of fuel it shouldnt be the case.
>>> 
>>> -Cody Forbes
>>> 
>>> On Sep 21, 2012, at 12:41 PM, Louis-Alain Richard <5145727795 at bell.net>
>> wrote:
>>> 
>>>> Spent the night with my good friend Lucian, a mechanical engineer
>>>> that is a tech/sales trainer at BWM Canada. He also translate and
>>>> writes the teaching material from Munich. He knows a bit about cars,
>> let me tell you.
>>>> 
>>>> I've asked him about knock sensing in BMW engines and he said that
>>>> knock is monitored all the time. Even on the highway at part
>>>> throttle. More, he said the ECU will try to advance timing all the
>>>> time, until knock events are detected, and then back up a bit. It will
>> do that again and again and again.
>>>> That way, the ECU knows that it extracted the last bit of energy from
>>>> each liter of fuel for any conditions (temp, speed, gradient,
>>>> atmospheric pressure, etc).
>>>> 
>>>> This fact do confirms the theory that Premium fuel is not only for
>>>> WOT events, but is beneficial all time on an engine that is mapped for
>> it.
>>>> 
>>>> And regular gas is detrimental for such engines...
>>>> 
>>>> Picture the G37 IPL convertible that I drive this week. I'm SURE the
>>>> preceding journalist didn't fill her up with premium. At low speeds,
>>>> 25 mph, I can clearly hear knock with a steady throttle when the
>>>> 7-speed auto trans gently upshifts. And every time I accelerate the
>>>> tiniest bit... Sounds like an old Tercel from the 90's.
>>>> 
>>>> Fuel economy is appalling : 17l/100km in town, that is 14 mpg.
>>>> 
>>>> Will empty the tank this weekend and report back with Premium.
>>>> 
>>>> Louis-Alain
>>>> 
>>>> 
>>>> _______________________________________________
>>>> quattro mailing list
>>>> http://www.audifans.com/mailman/listinfo/quattro
>>>> http://www.audifans.com/kb/List_information
>>> _______________________________________________
>>> quattro mailing list
>>> http://www.audifans.com/mailman/listinfo/quattro
>>> http://www.audifans.com/kb/List_information
>>> 
> 
>