high octane fuel?
 

I have a 2007 Miata MX-5. The owner's manual says to use 95 octane fuel. My previous 1999 MX-5 had no such requirement. Does this engine really need the higher grade gas? Has anyone used 87 octane routinely and found a difference? Thanks. Jim

If it recommends that fuel, it must need it. I would expect that if you put 87 in it would start knocking and running rough.

Surprised it specifies 95.....tough to find anything north of 93 here in Michigan.

Even here in the oil capital of the world, it is hard to find 93 sometimes.

If it is recommended, odds are that the valve and ignition timing are such that the engine will knock and ping, as SST stated before me, without premo fuel.

There are no cars sold in North America that require 95 AKI fuel, and there haven't been any for decades. So, a few possibilities exist:

1. Your car was originally built for the European (or other non-North American market) and your Owner's Manual is referring to 95 RON fuel
2. You've misread your manual

Most manuals will just say that you need premium, rather than specifying an octane. It does seem odd that it specified 95.

It seems that at least some Mazda manuals specifically call out the rating number; from the Owner's Manual of my 2009 (don't know if it is even remotely the same language for the 2007 Miata that the OP asked about):

2.3-liter turbocharger engine
Your Mazda will perform best with fuel listed in the table.
Fuel ------------------------- Octane Rating* (Anti-knock index)
Premium unleaded fuel ---- 91 [ (R+M)/2 method] or above (96 RON or above)

* U.S. federal law requires that octane ratings be posted on gasoline station pumps.

This vehicle is designed for and requires use of premium unleaded fuel. If 91 octane fuel [
(R+M)/2 method] (96RON) is not available, gasoline as low as 87 octane [ (R+M)/2
method] (91RON) can be used temporarily for emergency purposes. Use of gasoline lower
than 91 octane [ (R+M)/2 method] (96RON) can decrease performance during its use.
Refueling the vehicle with the correct octane fuel a couple of times will restore vehicle
performance.

Except 2.3-liter turbocharger engine
Your Mazda will perform best with fuel listed in the table.
FuelFuel ------------------------ Octane Rating* (Anti-knock index)
Regular unleaded fuel --------- 87 [ (R+M)/2 method] or above (91 RON or above)
* U.S. federal law requires that octane ratings be posted on gasoline station pumps.

Fuel with a rating lower than 87 octane (91 RON) could cause the emission control system
to lose effectiveness. It could also cause engine knocking and serious engine damage.

My '08 Miata called for premium fuel, I routinely ran midgrade (89 octane) in it with no pinging or noticeable loss of performance or driveability.

Running regular (87 octane) may be pushing it a bit, but these days everything is computer controlled, so if it senses pinging it will adjust accordingly.

One option I used to save a couple bucks on fuel was to fill with premium, when the tank got below half, I'd fill with mid-grade figuring the average octane then in the tank would be about 91. On the next fillup I'd use premium and alternate each fill. That was back when gas was > $4/gallon, now that is is cheaper it's not as big a deal on the savings.