pilotedge

Hi all,


I know there are plenty of threads on both front and back O2 sensors, and people have recommended Amazon for buying the NTK ones.


My question is this. Why are the RX8 ones so much more expensive than other cars? Even when you compare to other Mazda models or similar cars.


The fitting is generally the same (M18x1.5) and wiring seems to be a standard thing. So are there really differences between makes and model of sensor? And what are they?


As an example, looking at Denso sensors, what is to stop me using a sensor for an MX5 in my RX8?
UK prices (eBay, just for comparison)
Denso DOX-1449 (for RX8) - £150
Denso DOX-0317 (for MX5) - £85
Denso DOX-0323 (for MX5) - £110


All of these have the same fitting, and are front O2 sensors. What is the difference between these really?


The cynical side of me tends to think that it is too much of a coincidence that cars that are prone to emissions issues have more expensive sensors....


I would appreciate any info, or if I have missed an existing thread in my search, a link!


Thanks all

RIWWP

iTrader: (2)

The difference is narrow band vs wideband. Narrow band sensors are cheaper, and both sensors on an MX-5 are narrow band. The RX-8 has a wideband front sensor and narrow band rear sensor.

While Mazda might have been able to get away with a narrow band front sensor for the RX-8, it would have likely increased the engine failure rates, and it's a good thing that they decided to go with a wideband front sensor.

The difficulty passing emissions is just because the RX-8's engine has a lot of wasted and unburnt fuel every combustion cycle. The 13b's rotors are too wide, the flame front doesn't reach the 'corners' against the apex seal, leaving plenty unburnt. This was an even bigger problem for the FD RX-7, with the peripheral port engine, were the excess fuel is just swept out into the exhaust immediately. The RX-8's engine is side port, which traps the excess fuel in the engine for longer, trying to get it burned. It's better, but still under piston engine levels of emissions ability. The 16X rotor dimensions that Mazda has played with has a narrower rotor to solve that flame front problem, among other solutions.

pilotedge

Hi,
Thanks for your reply. I think I assumed all cars had a wideband front sensor.

The thing is, even compared to other cars' wideband or AFR sensors, the ones specifically mentioned as compatible with the RX8 are considerably more expensive. About double the cost. I have looked at various websites that explain how these things work but I can't really find anything that explains why a sensor for one car is different than another and much more money. Whether there are impedance values or sensitivity ranges etc etc.

It's just a little frustrating.

paimon.soror

iTrader: (15)

I wouldn't be surprised if the front o2 for the RX8 also has some specifics to handle the hotter temperature output of the exhaust stream. This would also contribute to cost.

RIWWP

iTrader: (2)

Pilotedge,

Paimon's point is one I'd agree with. Our exhaust is much much hotter than other cars with factory sensors.

It's not the only part of the 8 where something is much more expensive than "standard" cars. $20 per spark plug for a piston powered car is moderately ludicrous, as another example. And that is without any dealer markup, so it isn't just Mazda's choice.

Take heart though, some stuff is cheaper. Pistons, head gaskets, valve springs, ...