O2 Sensor Location on Racecar
 

Hi Gang, I have a Spec Miata that I've switched over to a megasquirt pnp and a few other bolt on go fast goodies for a PTE car. I just re-ringed the engine so everything is tore apart and can be reorganized, but I have a lurking question that's been annoying me since I bought the car: The PO has a wideband sensor AFTER the mid pipe. I have been searching for a "why" but I can't figure it out. Is there any reason I shouldn't ditch the factory O2 in the manifold and place my wideband there instead? Since I'm on the megasquirt, it's doing all the math off the wideband, but is there any benefit to it being way downstream like that?

Put the wideband sensor in the stock O2 bung. Plug that rear bung. You don't want it that far back on the exhaust.

There is no real benefit to having it in that location so far downstream. In fact, it's less than ideal because the information won't be as timely. Closer to the engine is better provided you don't melt the thing. Ideally you'd have a 4-channel wide band oxygen sensor setup (like 14point7 MegaSpartan) with one in each exhaust runner so that you can more easily handle individual cylinder tuning. But most people get by with just a single WBO2 sensor immediately after the collector. You can also add an thermocouple in each exhaust runner to measure EGT for less than the cost of doing a wideband oxygen sensor in each cylinder. It's nice to have both if you can afford it.

he probably put it there cause it's convenient
I did that many times.
never had any issues, with accuracy or otherwise. but you can use either location, doesn't matter much

Thanks for confirming my suspicions, I'll move it upstream and plug the hole.

Is the downstream sensor position originally "after the converter" on cars that have converters? That's the only idea I could come up with for why the OP had it so far down stream.

there's only a converter on the ca spec 99-00 with 2 sensors, 1 before 1 after. its really funky
most (all?) others, there's one right after the header merges and one in the back under the drivers seat area

Thanks for the clarity 18psi! Good to know, I though he had added it. I'm moving it around tonight, thank all!!