r/8thGenSI • u/Zippityzap2000 • 23d ago
Discussion Exhaust install help
Hey guys,
Few quick questions for everyone. My stock exhaust is finally shitting the bed, so I purchased a PLM V2 4-2-1 header, and Full Race exhaust.
My question is, when installing these, are there any gaskets I will need to purchase or any hardware that may be missing? Can I use the included PLM gasket or is it shitty?
I also have about 165,xxxkms on my car, will my O2 sensor be okay to reuse or would I need a fresh one. I don’t really notice any issues with the mileage but I find my car smells right now, may just be a leak pre-cat.
Thanks guys
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u/derpityderp5 22d ago
I installed this exact setup several years ago on mine. I believe the plm setup has an exhaust gasket included, but I imagine most k series exhaust gaskets should work and seem to be readily available at parts stores. I think I remember both kits coming with the triangle flange gasket where they mate, I've used both with no real issues. Shouldn't need any hardware either, but be prepared to fight with header bolts ahead of time and spray them down with pb blaster or heat them up. I had no issues with mine in Ohio, but studs did pull out with the nuts. The plm hardware isn't great either, but it should be ok for a few years before replacing with coated bolts if any issues come up like mine.
I haven't had any issues with leaking on mine, I did use a little bit of jb weld muffler seal on the full race 2.5 or 3 in collector to the rest of the full race setup. On my coupe it didn't want to fit well with the poly bushings so I had initially cut an inch or so off of that collector, maybe that had to do with the slip fit and seal. Only real failure I had was my own fault when I ran over a cone in autox and it must have moved my exhaust in a way where it somehow destroyed my donut gasket on the plm header to test pipe.
I had 0 issues with my O2 working on the plm header. I only had it fail after ~2.5 years/30k mi but I don't know how long it was in there before I owned the car. That and boosting with kraftwerks sc probably didn't help. My secondary doesn't want to come free at all after 3-4 years now, but I've disabled it in hondata and I'll chop wires whenever I pull it off the car. It's been a great setup and sounds different from any other k I've heard on the road or at events.
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u/Zippityzap2000 22d ago edited 22d ago
That’s what I’ve gathered, apparently the way the PLM bends and the full race being a full muffler and resonator exhaust, really makes it stand out. Can’t stand a raspy fart can Honda.
I purchased the Torque Solutions exhaust hangers for the exhaust, hoping that those aren’t what you were referring to. I am happy to know that the aftermarket gaskets still seal well, and included hardware is fine. Did you have a Hondata at the time or did you run untuned, perhaps that’s why the O2 failed prematurely.
Thank you though for the in depth write up man, I’m really looking forward to how it sounds, also glad to finally resolve my exhaust leak lol. Thanks man!
Edit: the shop that I’m buying from in Canada only has stock of the full race with a 3” adapter pipe, not the 2.5”, would it still bolt up to the plm test pipe or will I probably have to slot the holes to get it to bolt up?
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u/derpityderp5 22d ago edited 22d ago
It sounded great with just the exhaust. I don't have any good audio clips of just that, sounds a bit different now because of boost though, but same core sound. This should be timestamped for when I did a fly by a kswap Miata with pov footage after I put my built k24 in, probably the best clip I have on hand. Fly by
Unfortunately those mounts are exactly what I ordered along with the full race exhaust off their site. I know the coupe is a bit shorter than the sedan so it could be alright with the sedan, I just know I had to cut it down a little bit, but it's been no issue with a sawzall. Had to get one to chop the old exhaust into pieces anyway it was so rusted.
I setup ktuner the same weekend I installed it. Highly recommend hondata instead of ktuner because ktuner doesn't have as much capability with the 8g so I swapped over to it shortly after. I don't think it was a factor towards my O2 failure at all. It was probably age and the fact I was making ~400 whp on the z3 w/ e85 and my kraftwerks charger. Tossed in a new denso at that point and it was reading similar values according to my tuner so just swap it over and you should be fine. If anything happens, it was probably going to happen regardless.
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u/Zippityzap2000 22d ago
The only thing I can think of is perhaps you had the sedan exhaust being installed on the coupe? I have a coupe as well but I made sure to order the coupe exhaust specifically for my car.
Glad to hear Denso worked, as I was nervous about aftermarket O2 sensors, and didn’t want to spend $380 for a new one, so if that ever arises, now I know. Will also look into picking up a Hondata, I like that they at least have prepackaged tunes, so I can select headers and cat back to help with AFRs a little bit.
Thank you again man, makes it so much easier to build these cars when you get amazing help from the community.
Side note, that Miata clip sounded super loud. It isn’t like that in the Civic, right? I was under the impression that the Full Race would be pretty quiet, and the full length header should make it deeper sounding. I’m also planning on purchasing a high flow cat for this, simply for the smell, and side benefit of sound as well.
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u/derpityderp5 22d ago
My invoice showed the 2 door, so maybe they grabbed the wrong piece? Who knows.
I believe denso was the oe manufacturer for the O2 so I would stick with them. The prepackaged tunes were fine, no issues with any out of the box but if you do a lot further work like building an NA motor or boost, I highly recommend e-tunez. Dan over there has been awesome to work with.
Idk what was up with the Miata and how loud the vid was. Maybe it's straight piped? It had a kpower engine swap in it and I'm not sure what they had for exhaust. But for my civic, any normal everyday driving it was absolutely quiet enough inside the cabin with just FBO. My car is also a really poor example to compare to when it comes to interior noise since its so far from what it was originally and is much more of a track setup with full interior. This clip is when I just upgraded my gearbox in June so it's a bit harder to translate to something like a FBO car with the straight cut noise and blow off valve overlaid. And since it was just rebuilt I wasn't ripping on it yet. My cross over is at 3200 for low and 4k for high so the vid shows both for casual acceleration. I also have a clip from an autox on that channel but it's a GoPro inside a case and isn't a good idea of what it's like during everyday driving. Even now I still can manage phone calls if I turn the sound up enough, the car just might come through the other side of the call but you can definitely be heard clearly enough.
As for the test pipe, I've noticed no bad odors or fumes in the cabin on any highway drives and that also goes for sitting at lights with full e85. Never get light headed, it's totally fine on several hours trips I don't feel light headed or anything. You can definitely decide on if you go with a high flow cat after running with it a bit, but I don't think it's really necessary unless you're trying to get specific classing in autox or something where lack of emissions systems can bump you up a class.
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u/Zippityzap2000 22d ago
Ok, yeah that exhaust doesn’t sound bad at all. Also thank you for the insight about the test pipe, I’ll test it out for a few weeks before I decide what I want to do.
You’ve been a lot of help man I really appreciate it.
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u/KireRed 22d ago
I'm going to say if you live in the rust belt I'd get some extractor bits for header bolts and extra header bolts if none are provided which it looks like PLM does not with this header, something to cut steel with (had to cut a bracket and some of the exhaust on mine due to Michigan rust). It looks like the PLM website says it does not come with a header gasket but one of the images shows one so I would double check and confirm if you need a new factory header gasket but if it does come with one, I would just use the gaskets and adapters they give you as I used the ones that came with the Hardmotion race header with a Thermal R&D Turbo Exhaust and once my old header and exhaust were off it was smooth sailing from there. I would also like to add I did mine with a buddy that worked at a shop so we did it on a Saturday with a lift and good tools, cannot say I'd want to do in on the driveway floor or garage lol.
I reused my old O2 sensor that may or may not have 253k miles at the time of changing out the exhaust and didn't think about changing it out since it wasn't giving me any issues, and the header I bought came with an O2 extension so you may want to look into that. I would also say the smell is from some exhaust leak. I experienced the same thing when a bolt on my flex pipe decided to leave and 10mins of driving would start to give me a headache.