[Miata] Regular vs Premium after 2001

[Keith Tanner]

Two notes:

- Mazda made much more comprehensive changes to the car between
1999-00 and 2001-05 than a lot of people think. As I mentioned
earlier, the ECU is of a totally different family.

- Knock is not always audible to your ears, especially in loud cars or
heavily insulated sedans.

Keith

On Dec 4, 2007 6:42 AM, John Freas <john.freas at gmail.com> wrote:
> Previously on Regular vs Premium, Paul Levasseur <plevasseur at cinci.rr.com>
> said...
>
> > The manual for my 2002 recommends 91 octane, however it also states that
> 87
> > to 90 octane fuel can be used with a slight loss of performance.
>
> As far as I can tell, all they've done since the '99 introduction is allow
> the ECU to do the same thing that we had been doing with NA cars for years;
> run advanced timing and listen for knock to adjust the setting if necessary.
> The way they set up the table is probably on the conservative side, but
> depending on how confident they are in their knock sensor(s) they might have
> become brave in later years.
>
> If they mention only a "slight loss of performance", which I've heard
> before, it suggests to me that there isn't a big change in timing between
> the setting used with Premium and that used with Regular.  That said, there
> is no way that the car can know what grade of fuel you put in the tank, so
> there really isn't a "Premium" setting or a "Regular" setting, the car
> simply listens for knock and retards the timing when it is detected.  If
> it's like computers that I've seen, it retards the timing aggressively at
> first and then once the knock stops it advances it again gradually until the
> sensor goes off again or until it reaches its 'no knock' setting, all the
> while filling in the learning table for future reference.  It doesn't have
> to stop there either, depending on how sophisticated the ECU is it could
> reduce fuel delivery in cases of severe knock, again doing automatically
> what we would do as drivers.
>
> Should you rely on a knock sensor to set your timing?  Well in fact for NB+
> cars you don't have a choice, but hypothetically no, ideally you would run a
> fuel/timing combination that is appropriate for the engine in all operating
> conditions.  That said, we have given that advice a wink and a nod for over
> a decade with the NA cars.  The engine has changed somewhat, and with
> increased compression the margins are narrower, but the concept is the same;
> don't let it keep knocking.  Whether it is your ear or a piezo-electric
> sensor on the block doing the listening it is the same process.
>
> Are you taking chances by running 87 octane in the newer cars?  I don't know
> but I really doubt it.  Mazda isn't so naïve as to think that their average
> customer will stop to read the owner's manual, let alone adhere to it.  They
> will design the car in such a way as to minimize warranty claims and for
> those who go to the trouble to read the manual they will toss them a cookie
> in the form of a "slight" increase in performance.  I can tell you from
> first-hand experience that the factory recommendation isn't always gospel.
> Our OTM is a 2001 Audi A4 Avant (station wagon) Quatro with the naturally
> aspirated V6.  Audi's manual and stickerage clearly indicate only Premium
> unleaded fuel should be used, ganz sonst ist verboten.  Research in the Audi
> forums however found a large number of drivers who's experience was that not
> only does the car not need Premium unleaded to run well, but some of them
> actually had problems with cold starts if they fed it Premium.  Following
> the rule of "use the lowest octane your car will tolerate", I have put
> nothing but 87 US Octane gasoline in the Audi from the day I bought it 3
> years ago and have never heard the slightest hint of knocking, pinging, or
> other trouble.  In fact the car runs great.  Am I giving up performance by
> not using 91 octane?   Maybe, I haven't compared, but it sure doesn't feel
> like I'm losing anything from the seat of the pants.
>
> YMMV, do what makes you comfortable with your car.  If I owned a NB or NC I
> wouldn't be feeding it Premium unless it had a turbo on it.  I'd be
> listening for knock just in case, but I sure wouldn't be losing any sleep
> over it.
>
>     -John ________________________________
>  John Freas
> 1992 YELLOW "Sting"
> 1995 Black R Package "Spike"
> Elizabethtown, Indiana
> - Standard Disclaimer Applies -
> Team LS1,2, SP, the Gap...
> I love my Miata girl and my Miata Baby
> "I have no idea what those dimple things on the windshield frame are for."
>
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