Best Gas Octane

i just bought a 2003 miata and the owners manual had to be ordered. which grade of gas would you recommend? 87 or 89 or 91 octane.....please reply..thank you

Starting in 2001 the Miata engine was designed to run on High Test or 91-93 octane. However it does have knock sensor and will adjust your timming if you use 89 or 87. I find a get much better milage with Shell V-power 93 octane. I can use the 89 but get a little less milage. It tends to knock on the 87 but I think given time to adjust it would run on it just fine just not as much power. Our compression ratio is 10:1 which is a little to high for 87 octane.