Most of us know when you buy the RB long primary exhaust system, it lacks an O2 bung. My question is do you only need to install one in one of the pipes?

 

Install the bung towards the flange, about 5" away, where it connects before the cat/connecting pipe.

 

Oops I shold have mentioned it uses the road race header which has dual pipes. Just wondering do I need two O2 sensors, one for the ECU and one for a guage? Or will one sensor be enough (with the guage wired in)?

 

If its your stock o2 sensor either pipe will be fine. The road race header is designed for a carbed race car. What a/f guage are you running?

I would suggest the innovative motorsports lm-2 dual channel (2 oxygen sensors)so you could have the precise a/f of each rotor so you'd have to weld a bung on each pipe.

Stock o2 with the autometer a/f guage is useless, that's what I had before and you can't make any judgement baised on it.

 

when you buy the gsl-se one they put a bung in the center section

 

FWIW I've got the full streetport exhaust setup, and run a Haltech E6K. For tuning purposes I wanted to use one O2 so I welded the bung in the muffler piping where the exhaust merges back into one. With this setup I get the AFRs for both rotors instead of just one. I don't use a narrowband.

 

Sounds like there are lots of options.

 

Exactly. Sam (dj55b) can tell you the potential problems of only measuring the AFR in one tube. He had installed Venom injectors (later found that these can have problems) and tuned his setup with a wideband. Basically, one injector was flowing like 820cc/min, but one of them actually only flowed 620cc/min. I believe that he happened to have his O2 on the richer rotor and tuned to that. The other rotor went lean and blew his engine.

https://www.rx7club.com/showthread.p...t=venom&page=9

Safest bet is to run a dual channel WB O2 or put the WB O2 sensor where the pipes merge near the muffler. This is fine on a WB. For unheated NB O2 sensors (like the stock GSL-SE one), the sensor needs to be hot to read correctly and must be located near the exhaust ports. Heated NB O2 sensors and WB sensors can work in cooler conditions.

If you are tuning a setup (carb or aftermarket EFI), wideband is the only way to go. If you where putting this exhaust on a factory EFI setup (say a GSL-SE), you could just stick a narrowband in one of the tubes.

 

Just a correction, I know this is bringing it back from the dead kinda, but I had my wideband after the collector, but having one side lean and the other one rich, the mixture of both made it at the right AFR after the collector. I didn't have my EGT's in there also which showed a difference between the front and rear rotor of about 200 degrees but assumed it might of been just a connection error with the thermocouplers or even one side had a tad stronger spark. Should of futher looked into things.

 

I was close. I guess I was thinking you had the O2 before the collector. Anyway, the safest bet is to run a dual channel WBO2. This way you can monitor both pipes. This will also let you know if an injector is clogged or if you have a clogged jet in your carb.

If you can't afford this option, perhaps a single channel WB02 where you collect. You could add a pair of narrow band O2 sensors up front and use a switch to periodically switch between the front and rear rotor. Narrow bands aren't great, but they should at least point out if something is really wrong on one of the rotors.

EGT is another great tool to see what is going on as well.

 

I have to correct myself in my first post, but i meant to say that I DID have EGT's in there and NOT "didn't". I should of looked into it but Injectors would of still been my last thing to look at. One lesson that I've learned though is to flow test every set of injector that I get in.

 

Well, if you're using a GSL-SE ECU, it's not very sophisticated. I sense the stock O2 sensor so I can see what state the ECU's in by just adding the Autometer gauge. You can watch warmup, open loop, closed loop (crossing counts between rich and lean) single-rotor cut at light decel, and full injector cutoff on heavy decel. All these things are clear on the cheapo O2 sensor.

They're cheap enough, why not just tap two bungs with two cheapo sensors, and get a double pole switch that will allow a gauge to sample between either. Cheap, and you can learn a lot.