Okie...

Given NGK spark plug heat ranges are part of the part number. Higher is colder plug.

Source: Extreme Motorsports
http://www.extrememotorsports.com/plugfaq.htm

My Mazda pickup truck (1989 B2600) uses a 5 range plug... BPR5ES-11 (Source: Haynes Manual)

The RX-7 uses an 8... BR8EQ-14 (Source: Duh)

What tha dilly yo? I thought rotaries run hotter than boingers.

Just for reference, the 2.6 Liter Mazda engine, I was told is a "Long Stroke" engine... I believe it refers to the stroke of the piston in the cylinder. Where the break between long and short is, I have no clue, but I know long stroke sacrifices RPM, but increases low end torque, which this engine has a suprising amount of for a 4 banger. Still learning boinger dynamics...

Funny thing... Both my old Hondas listed two spark plugs... One for Hot climate and/or high speed driving. One for normal use. I always got pinging on the normal ones. (Colder plugs) I got a lot less pinging on the hot plugs, and they always looked new when I checked them.

 

The heat range of the plug isn't how much heat it can handle. Its the amount of heat that the spark plug "holds". A colder plug will run colder since it disperses more heat to stay cooler. These are good for highway driving. The hotter plugs retain more heat. These are good for city driving, where carbon buildup is common. The extra heat in a high heat spark plug helps to keep carbon off.

 

B9EGV/B10EGV's are fantastic for rotary engines. I certainly wouldn't run anything hotter than an "8".