I doubt you'll have problems with shorty headers but I've only installed longtubes and used O2 sims to keep the computer happy. I'm running dual 3" cats on my 2000 SS with the longtubes and did the same thing with my old 96 SS.
I have the stainless emission's longtubes with AIR and EGR still hooked up. I put dual 3" cats on it and had it tuned and I had no problems passing inspection in NJ. I guess it depends on how thorough your inspectors are if they can tell the cats were moved to a different location or not. The ASM 3/4 length headers work well and might allow you to keep the cats closer to the stock location. The MAC's may as well. The true shorty headers really aren't a big hp increase over stock manifolds for the hassle involved. Which brand of shorties were you planning on running?
I've got SLP long tube headers with simulaters for the aft 2 o2 sensors and I pass emissions in IL. The long tube tuned length headers are great and delivered almost exactly what SLP advertised. I gained 4 tenths of a second in the quarter.
The shorties might work ok with normal o2 sensors since your not moving them that far aft. It's all about keeping the heat up. The long tube headers allowed too much exhaust cooling and I got some messages about cat failure, thus the sims. You'll know whether it's ok or not when and if you get an engine light.
The long tubes are tough to fit in but well worth it in my opinion. Be prepared to lose some ground clearance though.
I talked to a guy yesterday who was telling me about O2 extenders to keep the computer happy. I haven't looked online but I would assume Summit would have something like this.
Any advice for droping the k member? Sounds like a pain.
I bought the long tube, tuned length headers from SLP and I went the whole nine yards. Bought the headers, the Y pipe, the high flow cats, and the installation kit. Came with extenders for the aft 2 O2 sensors, gaskets, etc.
After installing everything, I had no trouble for a few months. But about 5-6 months in, I started getting cat failure codes. I then went to Summit and bought the O2 simulators for the post cat O2 sensors. They worked perfectly and the car runs great with no messages.
Overall, the long tube headers were worth the struggle it was to fit them in and the loss of ground clearance. Mind you, I still go out of my way to avoid a speed bump!!!
Not even going to mess with the shorties for the hp gain. Figure I can put the effort towards passing emissions with the long tubes. I can probably make some extenders for the O2's, but wouldn't mind having some simulators to hide just in case I run into problems down the road. Has anyone put some sims together, I'm sure they are just a series of resistors?
Why not just delete the rear O2 sensors all together and tune out the code? I did that on my 2002 Z28 (I have LT's and no cats) and don't have any problems. The rear O2 sensors only tell the computer if the cats are working properly and are not necessary to the functioning of the system.
The front O2's, OTOH, are required for the computer to adjust the F/A ratio.
Extending the wiring harness to reach back far enough is probably just an exercise in cutting and splicing wires. I got a very nice set of extensions with my SLP installation kit, but I think any quality wire and splice would suffice. I agree entirely with PowerWindows, the aft or rear two O2 sensors are just for warning the computer. As soon as I got an engine light I bought the simulators from Summit and plugged them in, all tucked up tight with the leads from the aft O2's tywrapped up so they look great for an inspector. Car runs great and it would take quite an extensive inspection to reveal that they do nothing. I didn't know you could tune them out through the computer though, that sounds like an even better idea. When I go to inspections here in ILL they just check the gas cap and plug into the computer, the computer tells them everything is fine and they pass me. Go with the long tubes if you ask me, and keep an eye out for low clearance.
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