skwidd

Random act of kindness?

I heard that the reason newer cars will not knock is because the computer will retard the timing to keep it from knocking. However, I am amazed that you get the same performance. I've been doing exactly what you have been doing, alternating between 87 and 91/93, and I find no difference in performance, which kind of amazes me.

Anyways, that's just my $0.02...

SDB

My vote goes with the "use the cheapest that works" group. The first 2000 miles I used 93, then 89 for 2000 miles, then switched to 87. I saw no difference in mileage (averaged around 18 mpg) or performance. I currently have 33000 miles with no problems.

I do use 93 on track days, don't ask me why because I really don't know but there must be a good reason (at 7 mpg it seems expensive though).

mysql101

getting better gas mileage is a sign that the car is retarding the timing. I saw 2 mpg better mileage when I originally lowered octane, but that varies depending on which brand of fuel I use. With shell it's about the same either way, so I'm fairly sure the car doesn't care if I use 87.

8_is_enuf

Absolutely no notable difference in performance or mileage. The manual says it will produce more power with premium, but I don't think that power differernce will translate into a measurble performance difference.

scremn8

i've been using the lower octane gas for two years and the car drives fine. dealer finds no problem with with vehicle when going in for service...

StewC625

On the price issue, the difference is so minor as to be no big deal in the long run, but that said, there's something off-putting about +$3.00 gas - and right now regular in my area is $2.94 and the premium is $3.15. Guess what's in my tank this fill?

Again, no measurable difference in mileage or performance.

Now on a different topic, I notice quite a noticable improvement in mileage when I am able to fill the car with non-ethanol-blend gasoline - here in the urban area around Chicago, it's all ethanol, but out of this area, it's not - it's good old straight gasoline, and I see an improvement of 3-4 miles per gallon - which, when you average 16 is a big difference.

Nodoz

i use high octane every time. that's what the book calls for. granted shell, bp, chevron, or other big name stations' 87 may be better than smaller companies out there, i'm still going to spend the extra $3. we ALL know a rotaries are very tempermental engines, and nothing short of mazda saying it's ok for anything less than 91 can go in my car is going to make me change.

Paul_in_DC

Raptor75

Mazda dose say this right in the manuel. 87 is fine to use.

mysql101

the manual says NOT to use less than 87. But 87 up is fine. 91 range is recommended but not required.

does this feel like a broken record to anyone else?

*clicks unsubscribe*

Aseras

Again part of the rotrary's original design in the 70's was to use very low octane fuel. rotarties actually like low octane fuel. in fact the lower the better performance to a point. it was not uncommon for people to run 81 or even as low as 72 octane in the original rotaries.

maxxdamigz

iTrader: (1)

Auto-ignition and octane rating is a multi-variable subject. It involves, but does not revolve, around compression ratio.

Gasoline is a manufactured product. So is steel. Where I work, we can get a 30% fluctuation in steel tensile strength based on what vendor we use even though they are all "A36". It's a fluctuation in quality. Some gasoline vendors will sell a "better" 87/91/93 octane than others. You can probably talk to someone who does turbo-tuning for a living and find out who has the best 93 octane in the area.

Higher octane raises auto-ignition temperatures. Octane is rated based on the occurance of knock and ping in a single cylinder test engine at XYZ operating conditions. It is compared to the % mixture ratios. 87 octane gas is no longer 87% octane. It is a chemical equivalent. This also shows why some vendors have better gas. Higher ignition temperatures can actually slow your ignition down some and sap some power (generally a small amount). The power loss/gain is akin to having the right rated spark plugs. The difference may or may not be noticeable. Auto-ignition, however, is a bad bad thing.

Whether or not your car pings with 87 gas has to do with the quality of the casting you have in your engine, the heat of your spark plugs, the humidity in the air, the spray pattern of your fuel injectors, and the ambient temperature. Then, there is how you drive, your compression ratio, and you ignition/chamber geometry. When Mazda says 91 octane, they have a factor of safety in there. At 91 octane they are comfortable in saying that a reasonable quality gas rated for 91 octane on a hot/dry day will not ping in an average rx-8 even when it's working hard. It's more or less something like that - probably more math involved.

So - will your car drive well on 87? Probably.
Is there a possibility that it won't? Absolutely.
The likelihood of having your ECU having to retard timing on 87? It could happen.
Will it retard timing on decent 91 octane? Not likely.
Does 91 cost more than 87? Yes.
Does 91 produce more power than 87? Yes and no. If your car pings at 87, yes, and if not, no.
Do I run 87 in my car? No.
Do I say people who do are morons? Absolutely not. You do what you are comfortable with. Personal experience is king.
Am I posting this because I really car? Not really. I'm bored at work waiting for a meeting to start.

I had a corn muffin. It was good.

ALP22

89 all the way here and no problems.
A variety of vendors, Hess, BP, and Chevron.

BTW, that corn muffin sounds gooooooood!