Exhaust Questions

[Roadkill]

I have a '95 SL2 with a 5 spd transmission. I am interested in swapping out the exhaust manifold for a header that was used on the early SL2's. I have heard that it is a simple bolt on swap out, but had some questions concerning this. The donor car is a '91 SL2 automatic trans, and the exhaust header looks to be in good shape. On my car the O2 sensor apparently monitors exhaust from all 4 cylinders. On the header, it obviously goes from four pipes, down to 2 pipes and then to one. When it gets to two pipes, that is where the O2 sensor is located on the header. I didn't see one for the other pipe. Apparently, it would only be able to monitor exhaust from 2 cylinders. Would this cause any problems for the computer. My car is a daily driver and with no problems. I don't want to quickly turn my check engine light on after going through the trouble of doing the swap. Also, about what can I expect as far as power gain? Is is worth the effort?

[sierrap615]

if you disconnect the downpipe from the manifold and look up inside, the O2 sensor is between the two pipes and reads from both.

it is not a direct bolt-up. it will bolt to the head just fine, but the downpipe will need to be welded to the cat.

don't forget new gaskets and check the torque after a few heat cycles, plus you may want to clean the carbon out of the inside of the header first.

[carguy83]

i've done this. its quite simple except i had to tap and thread the new O2 sensor in. very simple process. high flow cat is a good idea too!

[sierrap615]

Originally Posted by carguy83

i've done this. its quite simple except i had to tap and thread the new O2 sensor in. very simple process. high flow cat is a good idea too!

i've heard people say that, but my 94's O2 sensor fits right in....

[carguy83]

my 95 didnt... they did change some stuff from year to year

[Roadkill]

I made my own high flow cat. Actually, the cat went out a couple of years ago due to a faulty temp sensor that caused a rich condition. Apparently, there are 2 temp sensors on a 95 SL2. One for the gauge and one for the computer. The one for the computer was reading way cooler than what it was. Therefore this burned out the cat and caused it to rattle. I fixed that by running the car down the interstate and then coming home (I live close the interstate) and shoving a hose up the tailpipe and turned on the water. The cold water will shatter the honeycomb type material inside the cat. Repeat the process a few times and all that stuff gets fractured and blown out the tailpipe. I love not having OBD2!!

[carguy83]

haha. i love that as well... although it was easier for me to spend 34.95 on a high flow cat

[mythconcepts]

blah...get on ebay and purchase OBX 4-2-1 race headers there like under 200 now I think

[sierrap615]

Originally Posted by mythconcepts

blah...get on ebay and purchase OBX 4-2-1 race headers there like under 200 now I think

you may see one or two more HPs from the OBX, but the 91/92 OEM is more relible(OBX is known to crack)