I was sitting back and thinking about the OBD-0 header dilemmas after 20 years of the birth of the B16A engine. If you plan to run OBD-0 all the way, by all means the both 02 sensors should be connected and the ECU should read both sensors. The OBD-0 system reads the o2's in cylinders pairs. One o2 for cylinders 1 and 3, and the other o2 for cylinders 2 and 4.
Running one 02 sensor with the original OBD0 B16 ECU is NOT the way to go. The factory places them 8 to 10 inches from the exhaust ports. There are two OBD0 ECUs that use 2 O2 sensors, PR3 and PWO ECUs.
With the limited number of headers you can find with double o2 bungs, it is obvious you can see people start to become creative with their header mods. Buying a OBD-1 header and adding another bung on top does not solve the problem even with a wire extension. Say you have the one o2 hooked up to read a cylinder pair and one o2 on the down pipe. The first o2 will have the proper readings and adjust the a/f ratio properly. The o2 on the down pipe will have the mixed readings from all 4 cylinders. In turn, it wouldnt be able to make the exact changes for the perfect A/F ratio for the cylinders its supposed to be controlling.If you stay with the OBD-0 ECU, you need to weld two bungs in the custom header up near the head on the original spot and wire the two O2 1 wire sensors. Problem solved. Just like the photo below.
Your Spoon, Mines, Mugen, Feels variant chips/ECUs might not even look for O2 sensors. Those were fuel-drinking racing programs and for the most part they dont care for O2 readings. So if you do not get a CEL, does not mean they are working fine. Just peep at your fuel gauge and start to worry.
If you care about mileage, then forget the variant chips and racing ECUs and install the 2 O2 sensors where they need to go and wire them correctly. Speaking of mileage, o2 sensors are wear and tear parts. When was the last time you change them? Old sensors likely gonna hike your mileage unknowingly.
Looking at the last photo is a common sight at your buy/sell local forums. OBD-0 headers sellings for more than RM1k in my opinion are just not worth the money. If you do not mind the condition, by all means proceed with the purchase. If you are a restorer, it'll need some work done. They dont make anymore aftermarket headers for the OBD-0 engines.
These days you can buy or custom a local header with less or the same price of the old, scraped, cracked and rusty header. By doing that at least you know the quality and prepare for wear and tear issues in the long run. Maybe some people are obsessed with the JASMA tag that is why anything non-JASMA aint worth to buy *chuckles*.
Getting an OBD-1 header with one o2 sensor bung is one story. Not clearing your cross member is another headache for EF/DA models. New OBD-1 race extractors have long and big primaries plus lower bends to the ground.
If you dont mind drilling and adding bungs on the OBD-1 header, then its fine. Getting a traction bar to clear the cross member is another additional cost.
If you plan to go for Hondata S300, be prepared to buy a few things for the conversion. Not cheap in total cost but you have full control of your engine setups in the long run. Driving an EF/DA can only be fun once you get all these bits and pieces completed before you even start to mod your engine seriously.
OBD-0 or OBD-1, your setup, your result. There will always be limitation if you limit yourself to OBD-0 setup. Likewise, the quest for more power will also be limited.
JASMA - The standards primarily to meet the legal regulations regarding vehicle and traffic law and safety standards for road vehicles, motor vehicle voluntarily. http://www.jasma.org/