Miatas and premium versus regular gas

I bought a '96 last summer and have run it on 87 octane since. Runs fine.

The 2002 calls for high octane....the highest I can get around where I live is 91. I filled up on the way home from work and the 87 was $1.49, 89 was $1.59 and 91 was 1.69. It took 9 gallons to fill the tank...for $1.80 it wasn't worth being concerned about.

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Hey I bet I could start a fight... We'll give you some more softwood for some of your cheap gas. Up here we pay about $1 for a litre!

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There are a lot of differences of opinion on this issue. Mazda designed the

2001 and new MX-5s to run on 91+ octane gas.( I don't think you need 104 octane gas!) Mazda design engineers know which fuel octane will provide the best performance and reliability for the car. Your MX-5 has a knock sensor that retards the timing when knock is detected, to prevent possible engine damage. Running a octane gas that is lower than recommended may reduce your effective miles per gallon and also reduces engine torque. It also causes increased engine temperatures that could cause damage when driving in extremely hot summer weather.

I passed a '97 Eldorado yesterday with the 4.6L Northstar motor. These cars have a knock sensor also, but I could easily hear the "pinging." Why would someone spend that kind of money for an automobile and run it on 87 octane?

Another approach to saving money on gasoline is to adjust your driving style. If you are getting only 20 to 24 mpg on your car and you need to make your money go further, it makes more sense to use the right grade of gasoline, and reduce the hard throttle starts and high rpm shifting that burns more fuel.

The older '89 through 2000 Miatas were designed to run on 87 octane. I average about 26 mpg in combined city/freeway driving on my '99, and that includes some spirited driving. Running higher octane than recommended does not increase power or miles per gallon on any stock MX-5.

Quite a difference between the engine in a '96 and the one in a 2003.

I specifically hunted out and bought my 2000 when all the dealers here had gotten in their new stock of 2001's because the engine had changed so much in 2001 (higher compression requiring premium).

Even so, > I bought a '96 last summer and have run it on 87 octane since. Runs fine. >

If it knocks/pings on regular, then use premium.

That's not actually true.

The knock-sensing ECU will attempt to run advanced timing and retard as necessary to deal with fuel quality. I know it's possible to get a little ping in my '02 on hot days under load, running 91-octane California pump gas, even at 91-octane the ECU is somewhat into retard.

Running higher than 87-octane fuel, you're likely to get a little better bottom-end/mid-range, though it might only be something you can measure on a dyno.

Cheapest regular gas in my area is 1.99 on the other side of the Delaware river, and as high as 2.19 around town on this side. Don't ask about premium!

Where is it they're selling premium gas a 1.69??? I might move...

The 1 should have been a 2 ...sorry.

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The current 1.8 engine runs 10:1 in stock form. It may be marginal with 87 octane since you may have compression creep with carbon buildup in the cylinders at the engine ages and you may end up with old gas with lower effective octane especially if you don't use the car on a regular basis.

I think part of the current recommendation comes party from the lawyers.

Looking at the Quick Tips booklet it reads 87 octane minimum.

Looking at the 2004 owner's manual page 4-2 there are two entries.

Under MX5/miata (sic) it reads "your Mazda will perform best" with 91 octane. "You may use a regular octane fuel 87-90 but this will slightly reduce performance."

Under MAZDASPEED MX5 it says:

"Use only premium unleaded fuel"

So, use whatever works for you. If you keep your rpm needle bouncing off the rev limiter, use premium. If you are cruising mainstreet on Saturday night, I thing regular is probably fine.

M. Cantera wrote in news: snipped-for-privacy@4ax.com:

I don't think so. Look at this part of Larry Gadbois post here:

His point about miles per gallon is important in these days of higher gas prices and your mileage will drop if the knock sensor does retard the timing. How much and what effect this will have on your wallet you'll have to figure for yourself, I'm in the middle of my taxes and numbers make my head hurt....

Ah, well, that makes sense. Good thing, too, I really didn't feel like packing....

Your mind is still in happier times...

Leon :)

Poor baby...

I filled up with CHEAP gas from Costco yesterday...

$2.34 for REGULAR 87 octane !

I'd be THRILLED to pay your Premium price for regular gas ! ! !

Actually, this is almost always precisely the other way around...

At high RPM, knock doesn't usually happen. Cylinder filling is most efficient at the torque peak and that happens well below the top of the rev range. Also, there isn't as much time for the mixture to get into the state where it will detonate (knock) when the engine is turning faster.

If you were to cruise along mainstreet at around peak torque RPM and then stand on it without gearing down...

...then you'd get knock!

Clearly. Also differences in experiences with individual Miatas.

In my 2000 Miata, I know that no matter what, no matter what weather, any way you slice it, it ALWAYS knocks with anything below 92 octane gas. The knock-sense and timing retard circuit does not seem to have the range to keep it from knocking under these conditions. I guess I presumed this was normal and should have had the dealer fix it under warranty before that ran out???

I also note a significant reduction in fuel mileage. I get about 20-22 with

87 octane (which includes not driving as hard simply because the knock scares me off) and I get about 24-26 with 92 octane and drive much harder.

I don't know about "designed to run"... But generally speaking, the compression ratio of the early 1.8's was 9.0:1 or below so I can see how they'd easily run on 87 but the 90-93's 9.4:1 might be a stretch, as would be the 99-00 9.5:1. Certainly 10:1 of the 2001+ cars is a stretch for 87 oct. I guess it depends on a whole lot of factors. All I know is, my 2000 NB knocks on 87 octane at all revs up to about 5K no matter conditions, and it even can knock mildly on premium gas with the A/C on in hot weather (in central TX, hot is real hot).