I've always found it interesting the factory installs NGK on one side and Denso's on the other. I'm not sure if or why the Engineer's would design the engine that way. I find it hard to believe this is not done intentionally. I guess if anyone who has changed their plugs on a Mexican built Tacoma would chime in...this would certainly answer the question if this was the intension of the Toyota Engineer's or just the way the plugs are installed at Nummi. Check out this thread...I find it interesting to see how the NGK vs Denso plugs respond to the same engine. It seems to me the NGK's run rich and the Denso's run leaner. I think when I replace mine at 30K...I may just spend the $12 on the Denso iridium's.