JG Pasterjak
JG Pasterjak Production/Art Director
7/30/19 12:10 p.m.
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So you installed longtube headers and now you don’t know what to do with those rear oxygen sensors. Here’s the fix.

We recently installed a set of Texas Speed and Performance 1 3/4” longtube headers and catless off-road X-pipe on our C5 Z06 project car. We’ll deal with that actual install in a future update, but for now, let’s deal with …

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Jordan Rimpela
Jordan Rimpela GRM+ Memberand Digital Editor
7/30/19 2:57 p.m.

It sounds great!

meldog21
meldog21 New Reader
7/30/19 5:24 p.m.

Nice job switching to the headers and X-pipe with a good explanation.   Now all you have to do is realign the mufflers so it doesn't look all cattywompus.

It might seem crazy, but I've found the only way to make the exhaust tips match requires 3 people.  One guy to eyeball from about 15' behind the car, one guy to hold the mufflers in the right spot accounting for "spring back", and one guy to tighten the clamps.  Or, you can just throw them up there and not worry about how the tips look.

JG Pasterjak
JG Pasterjak Production/Art Director
7/30/19 7:53 p.m.
meldog21 said:

Nice job switching to the headers and X-pipe with a good explanation.   Now all you have to do is realign the mufflers so it doesn't look all cattywompus.

It might seem crazy, but I've found the only way to make the exhaust tips match requires 3 people.  One guy to eyeball from about 15' behind the car, one guy to hold the mufflers in the right spot accounting for "spring back", and one guy to tighten the clamps.  Or, you can just throw them up there and not worry about how the tips look.

Oh yeah they're completely wonked in that video. They're about 60% better after tweak #1. i figure 2-3 more tries and they'll be near perfect :)

 

alfadriver
alfadriver GRM+ Memberand MegaDork
7/31/19 6:33 a.m.
JG Pasterjak said:

Finally, you’ll want to switch off 'COT', or Catalyst Over Temp protection. This is a routine whereby if the rear oxygen sensors detect a high catalyst temperature, the computer dumps more fuel into the cylinders to cool the cats down. Without those sensors in place, the computer can default to this mode out of caution, dumping way more fuel into your engine at full throttle than you need for optimum power.

JG- who told you that?

The sensors don't measure temps.  They generate a voltage based on the ratio of oxidants to reductants in the exhaust stream.  Unless GM is using some trick sensors, they don't measure exhaust temp- that's generally modeled, which is actually a pretty strong model.  The "dumping" of the fuel due to the removal of the sensor is a totally different thing that it thinks is being observed.  Especially if you are talking about the rear sensors- which is actually a pretty darned key part in the emissions control- it's not there just to monitor the catalyst.

I've read some of the HP Tuners threads- there's some good direction there, but there's just as much that is very wrong.  

While taking out the cat over temp protection is the correct thing to do for a motorsports calibration, the logic of why to do it is not right....  Just not related to the O2 sensors at all.  (Well, except that they, too, have temperature protections put onto them, just like the catalyst and the exhaust manifold.)

StuntmanMike
StuntmanMike New Reader
7/31/19 7:42 a.m.

Sounds great! Did yall sneak a cam in there at some point and I missed it?

Jerry From LA
Jerry From LA SuperDork
8/2/19 2:24 p.m.
alfadriver said:
JG Pasterjak said:

Finally, you’ll want to switch off 'COT', or Catalyst Over Temp protection. This is a routine whereby if the rear oxygen sensors detect a high catalyst temperature, the computer dumps more fuel into the cylinders to cool the cats down. Without those sensors in place, the computer can default to this mode out of caution, dumping way more fuel into your engine at full throttle than you need for optimum power.

JG- who told you that?

The sensors don't measure temps.  They generate a voltage based on the ratio of oxidants to reductants in the exhaust stream.  Unless GM is using some trick sensors, they don't measure exhaust temp- that's generally modeled, which is actually a pretty strong model.  The "dumping" of the fuel due to the removal of the sensor is a totally different thing that it thinks is being observed.  Especially if you are talking about the rear sensors- which is actually a pretty darned key part in the emissions control- it's not there just to monitor the catalyst.

I've read some of the HP Tuners threads- there's some good direction there, but there's just as much that is very wrong.  

While taking out the cat over temp protection is the correct thing to do for a motorsports calibration, the logic of why to do it is not right....  Just not related to the O2 sensors at all.  (Well, except that they, too, have temperature protections put onto them, just like the catalyst and the exhaust manifold.)

Also, "dump(ing) more fuel into the cylinders to cool the cats down" will have the opposite effect.

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