Unique VX exhaust manifold

[briogio]

I've seen the original VX exhaust manifold and it's unique among Honda manifolds; all the exhausts come straight out (90 degrees) to a central chamber where the O2 sensor is put in the centre, at the top. Then it goes down into a cat. That leads me to think that Honda wanted to put their 5 wire O2 sensor in the highest heat location. As the original VX manifold is hard to find, I'm going to try and modify a regular 4 into 1, locating the sensor in that 4 into 1 hotspot, at the top, then heat wrapping it to keep it hot. Has anybody done that?

[frank316]

Why would you want to put the o2 sensor in the highest heat location? If there is no exhaust leaks the o2 sensor is going to see the same amount of oxygen on down where there is less heat (hence longer o2 sensor life) that right at the motor. Not sure about something economical and naturally aspirated, but put a wideband too close to a turbine housing on a turbocharged car and you can kill a sensor in really short order. I.E. a few full throttle passes. Most wideband companies suggest the sensor be at least 16-18 inches away from the engine for heat releated reasons.

Ben

[usergone]

On my jeep 2.5 (naturally aspirated and vaguely economical), the O2 sensor is put right on the exhaust manifold, which is no more than 14 inches from any cylinder, and it seems to last fine.

Granted, my jeep comes stock with a 3 wire heated sensor (heater power, heater ground, actual oxygen signal) and I have a 1 wire sensor on it now (thank goodness for electrical manuals). AND, granted that my sensor is not wideband, as you mentioned.

To answer briogio's question, I can see where you are going with insulating it to keep it warm, and operational faster in engine starts/stops/starts. I would make sure to not block the vents on the sensor. If it breathes through the wires (as I believe most do nowadays) then you should be fine. Making sure you get a good seal on the sensor with a good new gasket and clean/smooth gasket surfaces should help keep the outside air uncontaminated by exhaust (but this whole paragraph is splitting hairs)

Here's a good article for people who want to know a little more in-depth about O2 sensors

[EdKiefer]

I don't think it mater much for mpg but the manufactures want the cat and O2 to get heated as fast as possible . My 08 Accord the O2 is like 6" from head but thats because there is no header manifold and the cat is like only 12" max from head .
Most turbo cars have O2 in the down pipe within a ft , many are inches from turbo but have not checked with vehicles with WB O2 .

[briogio]

Well you can see that Honda put the sensor in the hottest place possible on the stock VX manifold, so I want to duplicate that, I'll still have the cat under the engine like most of the other 92-95 Civics (just bought a new one). Thanks for the advice about blocking the vents, didn't know that, I'll check out the article too.
Thanks again