HKS Downpipe and placement of Wideband O2 sensor

debrucer

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I am installing an SLC Free B wideband controller which uses a Bosch LSU 4.9 O2 sensor. That sensor has an operating temperature of 740 to 820 with a perfect target being 780. The company (14point7.com) sells a version "C" (although, harder to get, maybe discontinued) which uses a different O2 sensor (LSU 4.2) whose range is lower, and perfect target temperature is 750 degrees. Right off the bat, the over-lap of the ranges makes the decision hard, but, I've got the 4.9, not the 4.2, so that is what I will be using. My downpipe is an HKS original... to my knowledge, the one that all the others are copies of :). The mounting boss in the HKS pipe is about 8 inches behind the turbo (7mgte) and the instructions for the SLC say the sensor should be before the cat and 36 inches behind the turbo. I have two weld-on bosses coming and plan on having them welded in at two feet and 3 feet, and to plug the one I don't use (as well as the original). Frankly, 780 degrees of heat in my downpipe sounds insane, but, surely the designers know something about it. Short of trial and error, how would YOU position this sensor considering the facts and requirements? It also has to be on the pipe between 10 o'clock and 2 o'clock. That might not sound like a problem, but, the engine has been on the stand for so long that I have no idea what the clearances are two and three feet down my front pipe :) Anybody have productive advice for me?
 
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debrucer

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Completed the last step in California registration yesterday with a pass on the SMOG inspection with everything visually stock. Now it's time to switch exhausts, weld the bung on the downpipe, bypass the stock ECU and get her running on my Speeduino. This thread received no responses in the year since I wrote it... and I'm not any closer to answering the question. On the plus side, I am learning to weld, and I've done a little practice on aluminum. Now, if I can confirm that HKS downpipe is aluminum and not some exotic alloy, I will no longer have to "have" someone do the welding.

I would still like to hear how such a requirement can be met. I could be several hundred degrees off and not know or have control over.

How would you go about selecting which sensor to use and why?
 

debrucer

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I can finally figure out the position for my wide-band O2 sensor. Specs say 36" behind the turbo, but they also specify a heat range. My plan is to weld two bung on this front pipe. I think I'll be safe in picking the position at 2:00 next to the transmission. I'll do the second bung at about 24" which I'm guessing will be hotter.
7mgte-r154-09152019.jpg
 

suprarx7nut

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I should have chimed in a while back. Here are my thoughts and experiences.

1. Wideband sensor location isn't as critical as the instructions may let on. Mine was installed about 8 inches after turbo (where many widebands end up). It performed fine for years. I had stock ECU and no piggyback and the wideband read exactly what I'd expect the entire time. Being too close to the turbo may introduce more heat and shorten sensor life, but it's not an immediate death sentence by any means. It also won't introduce a huge offset. If you keep your tune conservative you should be just fine.

2. The downpipe should be steel of some variety, not aluminum. Some exhaust components are aluminized steel, but I've never seen something that's simply aluminum. The exhaust gases are too hot. I'd expect an HKS product to be steel or stainless steel.

3. Exhaust temps - you can measure with an EGT sensor. On extreme setups, you might have an EGT sensor in each exhaust port in the manifold and another in the downpipe (7 total). Realistically, most folks don't bother at all. As a data nerd, myself, I'd love to have a sensor in each cylinder port and another in the downpipe just for fun/learning.

Good luck!
 
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debrucer

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I will check again on the front pipe. I presumed it was steel when I ordered the bungs originally,, and it was only recently that I figured out I had the wrong bungs. Got two aluminum versions last week after determining it wasn't magnesium. That was done with white vinegar, if it bubbles it's not aluminum. It didn't bubble. I hadn't thought of "aluminized steel", and I'm sure I didn't test with a magnet.

Thanks for the input. Good info! Appreciate you very much.

Updated: A magnet stuck like steel :) Thanks again for the tip. I've been sweating learning to TIG aluminum, which isn't a bad skill to have, but I prefer not to burn this sucker up.
 
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suprarx7nut

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Cool, glad it helped. If it sticks to a magnet like steel, but looks more dull and silvery like aluminum I wonder if it's got a ceramic coating. That would make welding a bear. No idea if HKS offered ceramic coating, but it's really common in the custom shop, small batch runs you'll see in the aftermarket and I could see it being mistaken for aluminum depending on the color they used. My old ceramic coated Raptor Racing downpipe looked a lot like aluminum.
 
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