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I'm considering putting a better exhaust system on my 96, I'm thinking about headers, eliminating the two catylitic converters and the big resonator or whatever it is that's between the converters and the mufflers, and install high flow mufflers. It has three oxygen sensors, how do I go about eliminating those and avoid having the computer turn on the check engine light? I heard that there is something available that plugs into the oxygen sensor wiring and tricks the computer into thinking that the oxygen sensors are still there, is that true? Even if I went with headers that have provisions for the oxygen sensors (are they available?) there will still be one oxygen sensor left to either connect or disable. I'd like to just disable all three of them if possible. What kind of power gain and performance gain should I expect to see from it? Who has the best deal on the headers and where can I get the things that plug into the oxygen sensor wiring to trick the computer into thinking that the sensors are still there? By the way, the car is registered in an area that doesn't do emission testing so I don't have to worry about that. Any help is appreciated.
1) Headers are a good idea. You can expect a "seat of the pants" feel after the install. I like anything Stainless Works with long tubes. Yes, they are expensive and worth it; install ease, fit, finish.
2) Keep your O2 sensors and yes, headers will have the bung holes already threaded. You car will run poorly with out them as your ECM won't accurately read the air in and air out of your engine; rich/lean problems.
3) For the rest of the system, you can't go wrong with Corsa. Again, expensive but well, well worth it and will bolt right up to the SW headers and very low drone.
4) you can get a system without cats.
I did this identical system on my 91. Super happy and zero regrets.
Some headers have the bungs in them when you buy them. Others don't, but you can get them installed for pretty cheap. You need to keep the two upstream O2 sensors for sure. As noted, the engine must have these to run properly, regardless of whether you have cats or not. The downstream sensor is just there to assess cat function. Without cats, it is of no use. Even with cats you'll get a check-engine light without a downstream sensor. It won't impact the way the car runs, but it won't pass an emissions test (understood that this won't affect you). The only way I know of to turn off that diagnostic test (to eliminate the code and CEL) is to turn it off in the PCM calibrations. On a 96, the only tuning software available to do this now is Jet DST. It's expensive (~$400), but it works very well.
Some headers have the bungs in them when you buy them. Others don't, but you can get them installed for pretty cheap. You need to keep the two upstream O2 sensors for sure. As noted, the engine must have these to run properly, regardless of whether you have cats or not. The downstream sensor is just there to assess cat function. Without cats, it is of no use. Even with cats you'll get a check-engine light without a downstream sensor. It won't impact the way the car runs, but it won't pass an emissions test (understood that this won't affect you). The only way I know of to turn off that diagnostic test (to eliminate the code and CEL) is to turn it off in the PCM calibrations. On a 96, the only tuning software available to do this now is Jet DST. It's expensive (~$400), but it works very well.
You would think that it would have 4 oxygen sensors instead of 3 because the downstream sensor is behind only one of the cats. I guess I'll have to add a fitting in the exhaust pipe for it.
We all have heard horror stories from guys who remove their main catalytic converter and have the dreaded Drone from then on.
I still have the two small ones on the y pipe and an aftermarket Hi Flow catalytic converter connected to a Chambered exhaust system. The exhaust note "Sounds" like a Corvette should and is not obnoxious inside the car.
I gained almost 14 hp in the swap and I have been able to beak into the 30 mpg range with an automatic 1988 Corvette.
Headers (LT really are needed if you do heads/cam/intake (if not they will some added HP, but not 40HP, more SOTP)
ARH & Stainless work = $$$ ($1200+)
Melrose, EM & TPiS = around $700 - $800 (coated)
Add a X-pipe in place of the resonator and hi-flow cats
Go with the stock system from there(very free flowing, 2.75 "), you can a cat back later (Corsa = $1400+...2.5") and the only thing a catback will do is for sound (no reall HP gains)
You would think that it would have 4 oxygen sensors instead of 3 because the downstream sensor is behind only one of the cats. I guess I'll have to add a fitting in the exhaust pipe for it.
After checking into what headers and exhaust stuff costs for it I might have to change my game plan. I had no idea that headers and an exhaust system would be so expensive for it. Now I'm thinking about just hollowing out the converters, replacing that big resonator or whatever it is that's in between the converters and the mufflers with two pieces of straight pipe, and putting some high flow mufflers on it. That should remove all of the restrictions in the exhaust system and give me a decent performance gain without going broke doing it.
You would think that it would have 4 oxygen sensors instead of 3 because the downstream sensor is behind only one of the cats. I guess I'll have to add a fitting in the exhaust pipe for it.
There's no guarantee that with cats further downstream due to long-tube headers, that they will light off as soon as the PCM wants and function as efficiently as it expects. IOW, you could add the downstream sensors and you might still get a code. Mine are considerably further downstream, because I have an X-pipe in front of the cats (better for power and sound). So I definitely needed to turn off the downstream sensor diagnostic.
Originally Posted by STL94LT1
The stock LT1 exhaust flows pretty well. If you aren't going to do headers, just leave it stock.
I agree. All that stuff you're talking about doing instead of headers won't add any power, but it will make the car ridiculously loud at cruise. It will suck.
Last edited by MatthewMiller; 09-16-2019 at 06:15 PM.
I agree. All that stuff you're talking about doing instead of headers won't add any power, but it will make the car ridiculously loud at cruise. It will suck.
For real? I'm not trying to be argumentative but I find that hard to believe. If the stock exhaust system is so good then why even bother putting an aftermarket exhaust on it? Why would people spend the big money that it costs if there is little or nothing to gain from it? There are five things in the stock exhaust to restrict flow, two converters, that big resonator or whatever it is in the middle of the exhaust system, and the two mufflers. Hollowing out the converters, replacing the resonator with two straight pipes, and putting on two high flow mufflers HAS to increase the flow by a fairly decent margin, I can't see how it wouldn't. Hopefully someone that did the things I'm talking about doing that has some before and after info either from the dragstrip or a chassis dyno will chime in and post the info because I'm really curious now about what to expect from it.
Yes for real. The dual exhaust on the late model LT1 is not considered to be restrictive. That's why you're not going to gain much for all the $$ you're going to spend.
For your consideration: If you're determined to remove the purpose of the cats and the central resonator then keep those stock parts and don't wreck them. Put on whatever high flow components you want but ..... (on a LT1) if you put on anything other than the stock dual exhaust system or a full Corsa you are going to have drone. So you depending on how much the drone impacts your driving or whomever you eventually sell the car to ... will want those stock exhaust parts to get rid of the drone. You don't have to take my word for it. Go back and read 10 years worth of posts here on the forum. Nothing has changed is the exhaust marketplace for our 95s.
Invest the money in headers and a cam or in a different rear-end ratio.
MM is not kidding. The stock cats, big resonator(which is straight through, FYI) and mufflers all flow better than good enough, for a stock or stockish, LT1. Therefore, power gains are minimal to nil in that area.
Why do poeple spend $$$ on exhaust systems? This is very simple and can be summed up in two reasons:
1. People like more sound
2. People are dumb
Most "car guys" want more exhaust sound. I don't think that needs further explanation. As for "dumb"...people but all kinds of cow-dung, fully believing that it will manifest some improvement, when some basic good information reveals that it will not.
Either tune/change/modify your exhaust to achieve the sound character/quality/volume that you want....or leave it stock.
Don't bother removing cats if not going with Long tubes. LT1 cats flow very well. my first exhaust upgrade was shorty headers stock cats, X-pipe in place of resonator and muffler deletes. sounded okay but a little boat ish for me. I since switched to Long Tubes Hooker Super Comp ceramic coated $850(painted are $500ish) they do not have 02 bungs but you can just buy the collector reducers with them already in there. and I eliminated cats and have full Borla system that has a resonator and 2 mufflers. for the record with the shorty headers system with cats my car dynoed at 318 RWHP with long tubes it dynoed at 309 but makes more torque, and HP earlier. I have video of both systems if interested in sound.
for the record with the shorty headers system with cats my car dynoed at 318 RWHP with long tubes it dynoed at 309 but makes more torque, and HP earlier.
First dyno graph is a stock result with the old shorty exhaust with cats X-Pipe and Eliminators, and then again after cam install.(before and after cam overlay)
the second sheet is that same after cam run and then after exhaust swap to LT and Borla, also added SLP Claw CAI. (before LT and Borla and after)
For real? I'm not trying to be argumentative but I find that hard to believe. If the stock exhaust system is so good then why even bother putting an aftermarket exhaust on it? Why would people spend the big money that it costs if there is little or nothing to gain from it? There are five things in the stock exhaust to restrict flow, two converters, that big resonator or whatever it is in the middle of the exhaust system, and the two mufflers. Hollowing out the converters, replacing the resonator with two straight pipes, and putting on two high flow mufflers HAS to increase the flow by a fairly decent margin, I can't see how it wouldn't. Hopefully someone that did the things I'm talking about doing that has some before and after info either from the dragstrip or a chassis dyno will chime in and post the info because I'm really curious now about what to expect from it.
First dyno graph is a stock result with the old shorty exhaust with cats X-Pipe and Eliminators, and then again after cam install.(before and after cam overlay)
the second sheet is that same after cam run and then after exhaust swap to LT and Borla, also added SLP Claw CAI. (before LT and Borla and after)
something else is going on there besides the LT headers. Either something is restricting airflow at high rpm or the ECM isn't adequately adjusting AFR. There is nothing inherent to headers that should make it die at high rpms like that.
09-15-2019, 06:17 PM
96 LT-1 performance exhaust questions
