Gas Story

What does your manual say? All I've ever heard is "regular 87 octane", but it may depend on what year Miata you have (?)

NW

#1 rule: read the manual.

What year Miata? My 2002 specifies premium unleaded; regular is OK in a pinch but power may be reduced (it's an artifact of the knock sensor and ECU timing retard program).

Of course, my Miata isn't exactly stock, so I have to run premium at all times (unless I wire the supercharger bypass valve into the bypassed position).

Dana

'90-'97 Miatas are designed to run on regular (87 octane). As long as there's no pinging, regular is fine. If ignition timing has been advanced past the stock 10° BTDC, higher octane may be required, especially in warm weather.

Later models have higher compression ratios, and the owner's manual specifies premium. If it pings on 89 octane, try 91.

The object is to avoid pinging. The tendency to ping is affected mainly by compression ratio, load, octane rating, ignition timing, and temperature. A car that needs 91 in summer may be able to get away with

89 in winter.

There's no advantage to using a higher octane rating than necessary to prevent pinging.

Technically, this is absolutely true. However, in practice, it may not be so cut-and-dried. In a knock-sensor equipped vehicle that retards timing automatically when it senses ping, the amount of pinging might not be easily noted by a human, but the vehicle is running with retarded timing. Using a higher-octane fuel may reduce pinging, and the ECU will run with greater advance and the engine will run better. So, it may *seem* that higher-octane fuel makes more power, when it's really the case that higher- octane fuel allows the engine to extract more power.

Dana

True, but Miatas with knock sensors ('99+) are supposed to use premium gas anyway.

The owner's manual for my 1999 says nothing about premium - just 87 octane or greater. I've always used regular and have no problems.

Sure, there's premium gas and there's premium gas. :-)

Dana

...

I take it the early models do not have a knock sensor?

On Sat, 06 Dec 2003 17:01:49 GMT, Lanny Chambers

Are there different octane rating systems? Here in France lead-free gas is sold as 95 or 98. Can these really be higher octane than your

89 and 91 or does Europe count differently?

Mazda recommends 95 which I've used for 5 years with no problems. The current cost is about $1.22 USD per LITRE.

Yup, US counts octane in different way. ASAIK Canada have the European version. US 87 = ca. 91 EU

89 = ca. 95 92 = ca. 98

Best regards, Kempi '01 silverfish,IL

Here are some hard cold facts for you:

You should be using the highest octane available in your area. Even with a first generation Miata that does not knock on regular gas.

The reason is that the demand will promote the availability of high octane gas.

HELP SUPPORT FORCED INDUCTION! BUY PREMIUM ONLY!

Leon

Folks,

Thank you so much for your replys. IT seems 1... I should go with what the manual says and stop listening to the buds... after all... is is my engine ;) 2... As with life... there is never a default answer for anything...

BTW... My Miata is an 02. Hopefully it will have a turbo charger in it soon. Maybe next summer... BUT I think I will beef up the brakes first. :)

"Barry" wrote

Didn't the premium recommendation come about the year variable timing was introduced? That was the year of the Great Exaggerated Horsepower Debacle (TIC), which was way after 1999.

Good reference. Thanks.

Leon

I run 93 octane in my '90B and an occasional 1/4 tank of 108 and the rest of the tank 93. With 14 degrees timing it screams run me harder!!!! I figure it bumps me to around 99. One of you mathematician/chemist types can tell me the truth??

-- Jerry Randolph '90B Red

This chemistry "guessing" frightenes me. I learned a lesson many years ago when I poured a bunch (more than a pinch) of 103 octane boost in the tank of my

75 MGB. Then I splashed in a tad (less than a bunch) more for good measure. She ran and screamed "RUN ME HARDER" just moments before her head gasket blew, and the blocked cracked wide open. What a thrill that was....

Jim Jim's Miata Web Page

If it does not knock at 93, why are you occasionally putting in higher octane? If it knocks at 93, I strongly recommend reducing timing advance.

I understand that most people running 14 degrees do not even need 93.

Leon