First top mount single turbo 370Z

ChipsWithDips

I think you were right the first time, it's not a huge plenum where you can see straight through to the other side, but I've seen myself, shining a flashlight in one throttle body, and peeking in the other, the light is visible(indirectly) from the other side.

Also, I didn't see in your pics, but where are the bank 1 and 2 wideband O2 sensors? If you have them sharing the same pipe after the two banks merge, the ECU will not like that either. It will try to trim one bank slightly, see no difference between the O2s, trim it more, see no difference, etc. until the banks are off by up to 25% or so.

Are you tuning with UpRev? I know with that you can log the fuel trim levels for each bank to check if something like this is happening.

jran76

There is definitely some shared space in the manifold to equalize the airflow, but there is also a distinct plenum on each side that feeds 3 runners. On the VQ35DE, it was pretty much open space above the runners and a single large plenum (which makes sense with only 1 throttle body).

A/F sensors are in each exhaust manifold/header, and O2 sensors are in the cats. The O2 sensors are not used for engine control, only the A/F sensors. I am pretty sure the O2 sensors are only for emissions purposes and are used to monitor the emissions (cats) performance. You can disable these in the Cobb/UpRev tuning software if you are running test pipes or HFC. I am using the Cobb AccessPort and tuning software. Pretty sure the OP is using UpRev (I will be soon).

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2009 G37S Sedan-6MT: Advan / Volk / Tein / SPC / Invidia / Cobb / K&N