Decat
 

Simple question really. I'm going to decat my car, and just put it back on when I do an MOT. But should I insert the Lambda sensor into the hole in the decat pipe or will this damage the sensor? The last thing I want to do is put the cat back on come MOT time and the lambda sensor being broken. I don't want to cause some funky over/under fueling situation or something. They aren't cheap, its like £50 quid for a used one on ebay.
I plan to take a trip to essex rotary to get a remap to remove the check engine light.

i always put the o2 sensor back in the mid pipe

And its never caused it any harm?

The lambda sensor is the front O2 sensor in the exhaust manifold.

The rear O2 sensor in the cat/midpipe is mostly just watching for catalyst health.

Just keep both O2 sensors in their usual places and you'll be fine.

Okay, i'll do that then. I'm really not putting much money into the exhaust system. The stock RX8 exhaust is super heavy though so its got to go. Cheap £275 ebay exhaust will do the trick. I'll just swap the cat back in when I do an MOT then. My biggest motivation right now is the clanging little bits of metal in the exhaust from the catalytic converter. Its really annoying and makes people look at the car like there is something wrong.

I would be surprised if ebay exhausts were any lighter, it's not like they're titanium. It's the same length of pipe made of roughly the same blend of steel. You might save 10lbs by removing the cat. If the heat shield is rattling, just remove it for free.

Well if you look at how massive the resonator is on the stock RX8 exhaust compare to an ebay one. There is quite a clear difference. I don't expect it to be a whole lot lighter. I'll just store away the original exhaust, heat-shields and stuff in my shed. Before I put the exhaust on i'm wrapping it in that green-ish 'titanium' fiber glass exhaust wrap which I highly doubt actually contains titanium. That should keep the exhaust hotter and allow for more detonations which sound awesome. The ebay exhaust is 2.5" bore throughout coming to a 3.5" bore at the tips. Will probably sound terrible, but I can't afford a racing beat exhaust and right now the stock exhaust is too quiet for my liking.

https://www.ebay.co.uk/itm/3-EXHAUST...8AAOSwUn9aJ85n

What's inside matters. The smaller one could be packed while the larger one is baffles. Which do you think weighs more?

You won't know until it arrives and eBay "bargains" are usually cheap for a reason.

Well aware its cheap for a reason. Its probably not going to sound very good as I said. But its going to be louder than stock which is really quiet. And for only £260 its not that bad at all. That listing has 100% buyer satisfaction, they also sell each part separately which has many more sales. Same story. I've seen people review the same exhaust system on youtube, the welds are actually pretty good. Racing beat would obviously be much better quality, my old MX5 had racing beat and it sounded phenomenal. But for now, it will do.

sonic had an ebay cat back years ago and it sounded like shit

Another thing to consider is the resonator. Supposedly, the RX-8 exhaust gas is hot enough to melt most packing-based resonator and then you will not have any resonation. There is a good reason why more expensive and high-quality mid-pipes like BHR mid-pipe doesn't use any packing. They don't last.

Maybe look around for used ones or save up for a better one?

I've been looking at a used Racing Beat midpipe on ebay for £120. By the time I have the money for it I fully expect it to be gone. But its my hope to find another like it. I don't mind buying used expensive parts over cheap new parts. But I just can't afford to buy expensive new parts.

So before you invest funds in a midpipe, have you done the basic survival items like coils, spark plugs and fluid changes?

No but the previous owner got it fully serviced at the mazda dealership and looking at the document they changed the spark-plugs less than a year ago. The car only has 38k miles so the transmission/diff fluid probably don't need doing although i'm going to. Oil is perfectly fine.
I'm planning on getting some d585 coils soon, they are pretty cheap ordered from the Greece and the adapter harnesses cheap as hell. I'll make my own bracket to hold them, shouldn't be too hard with a drill, nuts and bolts and a welder.

If funds are tight, survival items should be prioritized first.

Do MOT inspections include a sniffer test (probe inserted in the tailpipe)?

If not, you can probably get away with gutting the catalyst bed behind the rear O2 sensor (the sensor is inserted about 1/3 of the way down the bed so the computer won't know if you eliminate the portion downstream of the sensor).

Yeah MOT tests are very strict with emissions. Definitely need a fully working CAT to pass.
I was looking at the history documents for the car and everything seems to be been done properly. All the recalls have been taken care of. Full service etc. I think i'll probably do as you say and change fluids and do the coils first. It seems a safer bet.

For the coils, get yourself an HEI coil tester. No sense in replacing what isn't broken.
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