I used Baldwin Oil filters on my Ferrari for many years. I am happy to find out that they also make one for the Mazda RX-8.

The B227 (baldwin) replaces the Mazda N231-23-8020


They are about $6.00 and the quality is outstanding.

They are the only filter that works above OEM spec's on the Ferrari. I am going to get a few and try them out.

Here are the spec's if intrested.

Descriptions : Microlite Full-Flow Lube Spin-on
Contains : Anti-Drainback Valve
20 PSI By-Pass Valve
Thread : M20 x 1.5
O.D. : 3 (76.2)
Length : 2 27/32 (72.2)
I.Gskt : [1] Included

The anti-drainback is key due to the inverted position.

Plus is comes in a bright red

**disclaimer - I have no affiliation to this product or company**