What fuel should I run?

[Jessegroves]

I have a 1990 NA, I've only filled up twice using 95 and 91.

What do you guys run? What do you recommend? The engine is stock, zero performance upgrades installed.


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[Trackphotos]

Octane is only a measurement of how much heat/pressure it takes before the fuel will flash ignite/knock. The engine is designed for 91, so putting 95 or 98 in it will not improve performance purely by being a higher octane. It may however offer other benefits by way of different ingredients used in the more expensive fuels, detergents and other things. Generally though, there's nothing to gain on a standard engine designed for lower octane fuel, other than a slightly higher fuel bill. It wouldn't be a bad idea to run 95 if you were to take it on a track, just in case your cooling system turns out to not quite be up to the job, but I imagine if that were the case you might have bigger concerns.

[StanTheMan]

I got better fuel economy with 16 deg of advance. That's with 98. Do your maths.that was in the days where it was maybe 5 or 6 c more expensive. Now days it's far more.
I find a good compromise with 95. Engine seems to like it. Runs smooth. But it also depends on how often you drive it. Fuel seems to go off after a few months in the tank.
Currently I take about 4 weeks to go through a tank.

[Jessegroves]

Mines a daily car, I drive it most days, not long trips though, doesn't get dríven too hard either.. I think I'll stick with 95 when I can or else 91. I don't think I'll bother with 98


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[Apu]

95 is more than good enough. I run 98 only because my car has been turbo'd and was tuned on that...I'd go to E85 if I could find a convenient supply.

[Nevyn72]

Also remember that Mazda states that any pre-2005 vehicle is not suitable for ethanol.

So if you do want to use 91, avoid E10 blends.

I use 95 in my '02 Astina, the car runs a lot better than with 91 and is more efficient.
I tried stepping up to 98 but there was no further improvement......

I only use 98 in my MX5, but it's a turbo so......

[smy0003]

Slightly of topic, but I have trouble finding 95. 98 is easy to find at the big ones and also e10 at United, but I rarely see a 95 pump.
Am I going blind or are the big chains ditching 95 for 98 because of the extra profit?
*puts on tin foil hat*

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[Red Dragon]

BP has a yellow handle for 95
Caltex has a blue handle for 95
I never use shell so i don't know about them

[hks_kansei]

BP has a yellow handle for 95
Caltex has a blue handle for 95
I never use shell so i don't know about them

Red handle is 98 for shell.
Yellow I think 95.
Blue regular.



As for the OP re: fuel, 91 is fine, 95 will give better resistance to knock (not really a risk in an NA)
If you've advanced timing, run 95.

Most of the 98 octane fuels do have additives such as detergents etc, which can help keep sh*t from building up.
I tend to put a tank of 98 through maybe once every few months.

[wasabi]

I'm running 98 in my SE, but it's been tuned for it so don't have much of a choice

In previous cars I've had which could run anything from 91 & up, I still used 98 - Albeit, cost difference was a lot less then it is nowadays! Generally speaking the additional range I got with 98 justified the additional cost. Didn't do anything for performance as others have stated, but it felt like that cars ran smoother - Could just have been me though

Given the premium in price, the only reason I'd suggest running 98 in a stock car that doesn't need it is because of the mild injector cleaners & other bits & pieces that are found in them. If you're going through a tank of fuel every week or so, maybe run 98 every 2nd or third tank.

[smy0003]

Here's a question, I ride my bike a lot and the car sometimes has the same tank of fuel for a month or more, I use 98 because a) the amount of kilometers I travel makes the extra cost less noticeable and b) I assume 98 goes stale less quickly.

Is this actually the case?

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[rascal]

Generally speaking the additional range I got with 98 justified the additional cost.

Given the premium in price, the only reason I'd suggest running 98 in a stock car that doesn't need it is because of the mild injector cleaners & other bits & pieces that are found in them.

In my previous Mazda (KL V6 - stock as a rock), I got almost exactly 10% better economy using 98 over 91 (repeatable over 4000km test) .

Therefore on my usage if 98 is less than 10% more expensive than 91, then its actually cheaper to run the better fuel.
Throw in the added benefits of the better fuel and its a no brainer to use 98 all the time..
I haven't used anything other than 98 for years now..

[Steerpike]

Here's a question, I ride my bike a lot and the car sometimes has the same tank of fuel for a month or more, I use 98 because a) the amount of kilometers I travel makes the extra cost less noticeable and b) I assume 98 goes stale less quickly.

Is this actually the case?

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Nope. 98 does not go stale less quickly. 91, 95 and 98 are all made of the same components, just in differing proportions. In any case, one tank of any fuel will not go "stale" in a month or so. No need to worry, even if the fuel is a few months old. My mower probably still has fuel from last summer in it. Still runs fine.

[Magpie]

Like others my tune only allows the use of 98 or E85. However I struggle to put 98 in it these days and if I have to only enough to get me to a servo that sells E85 (United) of Flex Fuel (Caltex).