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The boards seem to say that exhaust mods are not effective. Cat back does not help. Mid pipe does not help much either, even with a cat back. Just changes sound. High flow cat (100 or 200 cell) is considered hit or miss. To start out, I had a factory manifold, Turbo XS midpipe and a Racing Beat Cat Back. The Turbo XS was too loud, and it was destroyed with Brandy (the green one); RIP Brandy). For Jessica, the blue one, I went with Racing Beat instead, and it worked well. I drove her like this for a few years and tuned the car. The Turbo XS Cat finally died, I replaced it with a 3 inch that mechanically failed, then replaced it with a Thrush 200 cell that has not failed yet.
BUT !!!!!
Reading through Team's Header theory about just getting the gas out, and having replaced parts due to failure in the past, and being pissed at the damn spring foolish POS connecter in the middle, and seeing a cheap header (Manzo), I decided to try a few things with my COVID free time. I wanted to play with header wrap, and I had some cracking on the flange of my exhaust manifold that was making it VERY difficult to get a good seal, and I found an option for that stupid POS spring connector. So, I did a couple of things. All parts were from Amazon. And I want to share.
The things I did.
I wrapped and installed the Manzo header. I also used the bracket do attach it to the trans (DO NOT DO THIS, it lead to a crack). I fought the passenger side long freaking sub frame bolt to a draw; and with glee and beer, I used a saws all to cut that stupid POS spring connector out of the middle of the pipe, including the reduced area on the RB Cat Back. I replaced it with a 3" flex connector like the ones you see in modern exhaust systems. The result is a header, a 3 inch mid pipe, a 3 inch - 200 cell Cat, a 3 inch flex pipe and a Racing Beat Cat back missing the first 3 or so inches of pipe.
The 3 inch Flex Pipe
The Results.
Once I put it all back together, found out how much header wrap smokes (car was not on fire), and started driving I noticed a few things. The Butt Dyno liked it (butt dyno always likes mods), the gas mileage went up a bit on the ultra gauge, and the fuel trims went a few percent more positive. This last one is the main piece of data, followed by the mileage. Over half of my commute is a 35 mph stretch of road with no lights. This reduces almost all the variables since I use cruise control. When the fuel trims go positive, it means that the computer has decided that more air is flowing than expected, and evens things out. This could be a fluke, but it was accompanied by an MPG bump and a positive butt dyno. And, towing my trailer to the track the next event, my overall mileage and range was higher than ever before. Car was quicker too.
Conclusions?:
The Good: I would offer that the exhaust is in 3 chunks, manifold, mid-pipe and Cat-back. And, from the factory, they are well tuned to work together. If you upgrade one part, it does not really make much difference. Even replacing 2 leaves the 3rd piece still set up for the lower flow rate. But, changing all three seems to make a difference. I have more air flow (based on trims), better mileage (based on observation) and quicker corner exists at the track. The first 2 are notable because they occur in what is usually the throttle governed range of operation, where it is very difficult to get gains out of the exhaust. The latter, corner exists, is more reflective of top end and those exits were up several mph over the last visit (same car, same tires, same track). It is significant enough that I have to change my corner approach and gear changes because I am running out of revs while still tracking out.
The less Good: the car was louder. I ended up wrapping the rest of the exhaust to get the noise down. It did change the tone a bit. That is it. There is no bad that I can tell, and it has been almost a year.
Overall:
The mileage increase is here to stay. The track performance is here to stay. The car revs to fuel cut without any power drop off. I would recommend this to anyone, and am interested in seeing other results.
But, this is a mildly tuned and likely ported motor. It came with the car, but I bought the car from Cam at Pettit Racing.
Right now I am happy. The car is way faster than I am, but as my back heals, I am getting better. And, I really do not want to go much faster unless I go full crazy. And, I cannot afford full crazy...
I also used the bracket do attach it to the trans (DO NOT DO THIS, it lead to a crack)
Mine lasts few months before it starts to cracks, and making the funny noises lolll later totally dislodge 2 inches of pipe....
I have Polyurethane filled Engine mounts it might accelerate the vibration cycle a bit tho.
Long story short, do not connect headers to trans, here is a reason RB remove this bracket.
The solution is easy to mention, connect headers to cat flag blots as they are stronger.
Based on personal examination during +1 year, rotary engine behave differently or at least with our ECU setup it dose.
My main concern when I bolt a headers was to keep heat out engine, never ever fool my self to get hp+ even I know
by doing so I would push my engine to leaner on lower RPMs. Decat alone makes car burn leaner even after ECU adj.
Another major concern is about thermal stress, with OEM manifold heat-shield designed to
isolated bay but still push air under shield to cool down manifold it self. Heat Wrapping headers is another mistake I made and again I was left
with other options.
I am interested in the leaning process with a header. This is definitely the case with an open loop system, but with a wideband, the ECU should immediately trim around it. That leaning, or getting more air through than expected, is what sent LTFT up a few percentage points. If it had not, yes, it would have been leaner. I will share that, at least with the 04 / 05 factory tune, you can get a lean spot around 6K with mods. That is because the flow limit in max calc load is too low. The ECU uses that number to decide if the MAF is lying. I declares it wrong if it goes beyond that number and just uses a lower number. This takes things lean, fast, especially at high RPM. Some cars will get better by 6,500 or 7,000. I fixed a buddies massive misfire problem with that one setting.
Regarding wrap, this was an experiment. If / when I do it again, there will be ceramic coatings and a heat shield.
with a wideband, the ECU should immediately trim around it.
On paper yes. Still, I don't understand why Mazda uses wideband !?
Important point is to reset ECU after this type of change so it would reset long term fuel trim.
Basically, ECU tries to guesstimate in the first place via other inputs, but shortly after it would back to perverse dials as it would find them useless! feedback on feedback....
Unfortunately, not everyone has the luxury of good ECU tune or adequate knowledge of use, they want to blot something shinny and see magic.
Regarding wrap, this was an experiment. If / when I do it again, there will be ceramic coatings and a heat shield.
The ceramic coating keeps rust away, however, don't hold your breath on heat isolation.
Factory headers utilize two pipes as doubled layers to use air as heat isolation.
I don't care about what other people saying about the lack of overlap in the primary ports, we could have overlap on the secondary or create overlap, but
the grave issue is on the middle exhaust port where two rotors are open together also they are interconnected all via air injection ports.
Surprisingly everybody thinks if there would be an overlap it should help cleaning in the intake area as it is opposite and it would push exhaust back to intake port as
it has way more pressure. My conclusion, even with overlap + good headers = loss of power in low/ certain RPMs.
I am interested in the leaning process with a header. This is definitely the case with an open loop system, but with a wideband, the ECU should immediately trim around it. That leaning, or getting more air through than expected, is what sent LTFT up a few percentage points. If it had not, yes, it would have been leaner. I will share that, at least with the 04 / 05 factory tune, you can get a lean spot around 6K with mods. That is because the flow limit in max calc load is too low. The ECU uses that number to decide if the MAF is lying. I declares it wrong if it goes beyond that number and just uses a lower number. This takes things lean, fast, especially at high RPM. Some cars will get better by 6,500 or 7,000. I fixed a buddies massive misfire problem with that one setting.
Regarding wrap, this was an experiment. If / when I do it again, there will be ceramic coatings and a heat shield.
I have a question regarding running lean at certain rpms after exhaust mods. Can I expect to see this on my S2 as well with stock header, mazsport catless midpipe and stock muffler soon to be modified to run as a straight through? Car is used mainly at the track so most of the time it us under WOT condition. Does this leaning out happens only under part throttle when ECU adjusts fuel based on wideband O2 sensor and not under WOT when it just uses programed fuel maps?
02-07-2021 | 01:28 PM
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