As I understand it, the rx8 comes from the factory with a wideband o2. We all know what happens when these cars run lean, and there's that nice space in the ashtray just begging for a gauge. Anybody installed one yet?

Nope, good idea though. Any idea of who makes them? I just hunted around on Defi's website, and did not see this type of gauge.

Defi has a 52mm a/f gauge.
Parts numbers are DF04103 (white) and DF04104 (black). This guy (http://www.gadgetseller.com/gauges/) sells gauges modified to be more sensitive, as well as digital ones that show the actual voltage.

Is the 3 part MazdaSpeed one (made by Defi) contain a A/F mixture meter? I thought I saw one....

...Or you can go about purchasing the Professional Lambda Meter by MoTeC, which runs for a slight over a grand. It's a digital meter that actually shows lambda or a/f value in numbers...

http://www.sakatamotorsport.com/Merchant2/graphics/thumbnails/mplmkit-sm.jpg