New Header Dyno Results

Alain - The Red Scorpion said:
I deleted the catalytic converter and installed this header (made in UK). I has no provision for an O2 sensor. Do I need to provide one? My X is 1980 with Fuel Injection and performance head by MWB. It started fine yesterday and seems to idle smoothly.View attachment 61244
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Wow that's one sexy header!!!!

The problem with headers on FI cars is that most of the time there is no factory-equivalent place for the oxy sensor. Put it down past the collector where the 2 pipes join into 1 and it might be too far away to stay hot (early oxy sensors are not heated like todays are). Put it closer to the source and now you're only reading one hole and not all four.

OTOH on our cars the oxy sensor doesn't have a huge impact like they do on todays cars, so I guess it all comes out in the wash :)
 
I'm with Dan, the O2 on this FI system does very little. You'll be very hard pressed to tell if it's even working. It really only affects the idle for emissions, nothing more. Therefore I don't think the location is as critical as with other systems. Like Dan and Karl said, either close to the head for a single wire sensor, or add a circuit to use a heated sensor so you can put it down at the collector.

I'd love to see someone in the US offer a nice header similar to that. Although it would benefit torque if the secondary tubes (two into one) were longer.
 
NeilMc said:
Doug is local and a fountain of knowledge about the X. I’ve been out to his shop several times to buy parts, get advice, and borrow tools. Attached is a picture of down pipe I fabricated with inspiration from SteveC.
View attachment 53538
The manifold was purchased from MWB as used/refinished. The 2-1 pipe is a new part from Yugoparts. The mandrel bends and flex coupling are from Vibrant, 1.75 in diameter. The exhaust flange is from Mandrelbends. The flange connects to the stock 1975 muffler where the test pipe would connect. I made a mockup from cardboard gift wrap tubes and then cut the sections with a bandsaw. A friend tack welded the parts. The finish welding was done at a Toronto shop named Kreater Custom Motorcycles that does beautiful work. The cost of this all-in is about $250 CAD, of which more than half was the welding. I’ll post more pics as complete my build.
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Here is one I took off a 74 X 1/9 SCCA ITD car. (complete with O2 sensor port. $20 plus shipping
 

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On my loooong tube header, I run the O2 sensor (wideband) on just one of the four cylinders. Works well enough.
Mounting it in the collector didn't work, even with the heated sensor. Sensor life was very short way down there.

Karl wrote above the the O2 sensor is not used at idle, Jeff said it is only used at idle.
I would argue that it does the most at a constant cruise, where it makes sure your mixture is correct not to kill the cat.
 
Ulix said:
On my loooong tube header, I run the O2 sensor (wideband) on just one of the four cylinders. Works well enough.
Mounting it in the collector didn't work, even with the heated sensor. Sensor life was very short way down there.

Karl wrote above the the O2 sensor is not used at idle, Jeff said it is only used at idle.
I would argue that it does the most at a constant cruise, where it makes sure your mixture is correct not to kill the cat.
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Do you have any sense of why the sensor failed early when it was mounted farther from the cylinders?

On all of my modern cars the sensor is quite distant from the cylinder head at the lead in to the catalytic converter. These last extended periods, I have a Yugo manifold which I wanted to put the O2 sensor just before the cat and now your experience has me doubting my intent.

Thanks.
 
Interesting question. As far as I know the heated sensors are intended to speed up the reaction time, therefore lowering emissions right after start up. I don't know if it has anything to do with their placement in the exhaust system. But I'm with you, it would seem a heated sensor could live further away without problems. Typically a failed sensor is either due to a buildup of carbon (e.g. a poorly tuned engine) or age related deterioration of the metals inside it (e.g. the 40,000 mile replacement). So I believe the only real function of placing the sensor close to the manifold/head is to retain enough heat so it reacts.
 
Bear in mind that these are wideband sensors, used on a hopped up dual carb car.
Below is a pic of the mocked up exhaust, note the postion for the sensor in the final collector.
We don't have any hard evidence, nor technical explanation, but two sensors failed in very short order mounted in that location.
Now it is located in one of the vertical primaries (all primaries have been fitted with bungs) and the new sensor has been working fine for a year or two.

I wouldn't be surprised if regular narrow band sensors are much more forgiving.
 

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For heated sensors, extra care must be taken or else their life will be significantly shortened. O2 sensor life in aftermarket applications can often be less than 40,000 miles- while OEM applications can last over 120,000mi before they become appreciably biased.

The two largest factors are the placement (there's a specific range of angles that it should be placed at), and heating strategy.

Generally the sensor should not be placed completely horizontal or completely vertical- though vertical is not as much of a problem as horizontal.

If the sensors heater is turned on while there is still condensation in the exhaust and on the sensor (following a startup), there's a chance that water may come in contact with the sensors element- thermally shocking it and cracking the delicate substrate. (Consider that it flashes from ambient temp to 750f as little as ten seconds!) You want the engine to heat the sensor and exhaust sufficiently to boil off any moisture, before hitting the sensor with the shock of the heater.

Most aftermarket controllers do an absolutely terrible job with the heating strategy- and keep in mind, the amount of delay necessary before the heater is switched on is entirely based on its position in the manifold. The further away from the head the sensor is placed, the longer you must wait before turning on the heater.


You must also be aware of the O2 period- a value the ECU uses for closed loop control that essentially, as a function of engine mass flow, tells the feedback loop how long it takes for the exhaust gas from a combustion event to make it to the sensor for analysis. Tuned wrong, with the sensor too far away for the given delay, you'll get a control loop which requires so much damping to not get into an overcorrection, that you're leaving a lot of fine control on the table. How this is tuned and changed varies by ECU type.
 
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Ulix said:
Why is horizontal placement bad?
Because of condensation?
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That's correct- a completely horizontal position greatly increases the chances that condensation may drip from the sensors own shielding onto the sensor element. The reasoning for not vertical is a little less clear to me, so I won't go down that track in fear of misleading yall...it's generally accepted but seems to be backed up by less evidence.
 
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