ILX header/downpipe options and reviews, piping dimensions by aomechmarine

By diyauto
( 2 )

25 minute read

ILX header/downpipe options and reviews, piping dimensions 

Compliments of aomechmarine @


So there is a wealth of Info on this subject on the different 9th gen Civic forums. BUT I wanted to have a spot for OUR cars. This is both a review/experience posting.

I had a Skunk2 header/downpipe on my K24 6 Spd Premium ILX. My car is lowered at about 1.5 inches with Swift Springs Japan for a nice lower profile and some better handling. I also have this FKX "X" frame suspension brace

Have the same front lower tie bar pictured too. So the reason I mention all this is because all of these pieces are in VERY close proximity to each other. Kinda like this pic. (This is a civic R18, anyone driving the ILX with the R20 with a header, their setup will look like this. Same frame and it shows what I'm talking about a little more clearly).

So my Skunk2 header literally split in half. I don't 100% blame Skunk2 at this point tho. It is possible that the car was low enough that (1.5 lower) that it was making contact with speed bumps, and slowly overtime taking hits caused it to bust. The Piping is larger then stock, AND i have these bars. my front lower tie bar is definitely scraped up. If you add in the thickness of the bar (around half an inch to an inch) to the area where the bar is, and where the header cross paths... Then at that specific point, its like the car is 2 to 2-1/2 inches lower. The stock piping for the header is 60mm so about 2-1/3 inches. This is a picture of the RV6 2.5 inch header next to the stock header pipe with its 2 giant catalytic converters.

The  Skunk2 header is 3 inches in diameter. so lets say its sitting about a half inch lower. That means that at that cross point (where the header and the lower tie bar meet/cross paths)... The header was sitting (as it was sitting in my specific car setup) at least about 2-1/2+ inches closer to the ground then stock. At that specific point, it's like the car is rolling slammed. BUT, I'm also driving the car normal, NOT driving it excruciatingly super slow over speed bumps like a car that IS lowered 2-1/2 + inches.

As far as the actual header, I actually had it installed, didn't drive it much, and then immediately like a week later had the exhaust bolted on. Right now my OEM catted downpipe is back on. So now I can compare. I can tell you that with this Skunk2 cat-less header, you can literally smell it wasting gas when it is brand new and it is breaking in. It is WAY louder, and you can feel a big difference with it on. Of the 3 basic bolt-ons, it will make the biggest gains and difference.

My car is currently much quieter and you can still hear the nice deep very sporty exhaust tone of the DC Sports  exhaust. But I do miss the header note. I go to car meets and guys running 3 inch headers and 3 inch exhaust on their Civic Si's have loud ass cars. Mine was loud, there's are louder. The header was definitely making the biggest sound difference. BUT, I was also still running faster then them. Not a ton, but still faster. I know that's not scientific, but still....

I will see if Skunk2 stands by their product build quality and gives me another one. At that time, I'll probably just sell it off. Although a loud car is fun, it draws negative attention from law enforcement. And you get used to the noise, so you don't always realize how loud you are. I also think I'm correct when it comes to my assessment of the header being about 3 inches lower (specifically in my car's setup) where it and the lower tie bar or X brace cross paths. Add in the fact that the shocks have room to travel...

See where I'm going with this? It's entirely plausible the header was low enough that it took some hits that eventually took it out. Another reason why I am not a big fan of daily driving a slammed car. Breaking parts on cars isn't fun or productive.

So in summary, when getting headers for your ILX - (and also exhausts)

1) think of the pipe sizing. Bigger diameter probably means more power gains.

2) Think of how loud you want or can stand the car being. Think of the positives of wider piping (nicer louder sound) and negatives of that (getting pulled over).

3) Think about how much you are going to lower your car. Think of how much height/ground clearance you will lose. That scraping noise you hear? Maybe its important parts like your header or exhaust scraping.

4) Emissions/exhaust smells. I would genuinely recommend you get a header WITH a built in high flow cat. The  Skunk2 header definitely was a polluter, and at times the smell crept into the cabin. Mostly I noticed this when it was brand new, if you ever buy a brand new car you will also have similar smells when you are first breaking in the exhaust. If you want max power, you probably don't care. I doubt the difference in power is much. If you want to minimize gas/ exhaust smells, get the catted version. And others mentioned this as well on the 9th gen forums. These smells were really annoying to me. There are 3inch piping headers with high flow cats. Depending on your state, you may actually pass the smog test just because you have a cat.

5) Think of what size aftermarket wheel you choose. If you get a 19 it will be easier to close that wheel gap, and you will be sitting a bit higher, a bit more clearance.

6) Think of and research available specs/info about the build quality. Especially since the Skunk2 did not appear to hold up. I had it for about a year and 3 months, maybe 15k miles.

7) cat-less down-pipe occasionally threw a code on my MID. Check exhaustsystem or something. Maybe the pipe was busted and leaking tho?

8)Catted version will keep some smells and emissions in check, but may also keep the noise down a bit (pro/con depending how loud you want)

9) some people have also mentioned a "HISS" or a "hissing" or a "raspy" noise... I don't believe I experienced this...or maybe It didn't bother me? It appeared to happen across various brands. Especially catless

10) 3 inch piping from header back seemed to throw codes sometimes on the 9th gen forums.

11) Some Headers come with defoulers. This is a plus that will help you NOT throw a code.

12) To minimize "rasp", CEL codes, and maximize the gains, add the intake and exhaust, and get Flashpro.
SO... to prevent these issues from happening AGAIN... I will most likely try one of these OTHER headers, AND upgrade wheel size...For other reasons as well, but gonna go for plus 2 sizing, especially for looks and for that added height /ground clearance. I like building the car with everything working well together.

13) If you have a 3 inch pipe, you may get some noise/rattling. to fix this, you'll have to get a rear mount. They run about $150. If you get a 2.75 this is maybe, if you get a 2.5, you should be fine. I experienced  rattles. It's annoying, and you may get used to it. Passengers will bitch about it. "OMG, WHAT is that noise?" That's WAY more annoying.

14)Drone - 3-inch piping tends to have more drone when you are on the freeway/highway WOT

15) 3 inch piping also with tends to burn/melt/warp the underpanels under the car. I've been to few race shops and they all told me this. The 3inch headers and exhausts do this. They end up sitting closer to everything, and it smells like burning plastic. I noticed it a few times. I think the 3 inch exhausts are probably the worst culprits.

16) If going Supercharged, you should be perfectly fine with 2.5 piping, wider is probably preferable. The "Street Build" supercharged ILX had no aftermarket intake or downpipe/header, both of which can fit with the C-T supercharger used. It only had an exhaust (Greddy Civic SI exhaust modded to fit, it's 70mm/2.75 piping), and it was making 250WHP. So if you have I/H/E, you can easily add a few (maybe 15-20whp) ponies to that and be fine. CT Engineering makes 2.5 inch exhausts for Civic Si's, and I've also seen people running superchargers with 2.5 piping headers on the 9th gen forums.

17) smaller piping tends to actually be stronger, since its "denser" per the area/ space it's taking up.

18) Pricing. It's relative. Skunk2 tends to be cheaper then others. But if your header fails/breaks at the welds, like mine did... How exactly are you saving money? Main reason i bought mine from Skunk2 was that it was within driving distance to go straight to the actual company and check it out in person. I got a small 10% or 15% discount for being the first ILX to try it on my car. I've actually found other threads now with others complaining about busted welds on their headers on comparable Civics.

19) Suspension bracing. Think of how bigger piping will touch or almost touch bracing, rub or almost rub against it. Think of how that can create annoying noises (clanging, squeaking). Think of how that can possibly damage the header or exhaust piping. Think of how that can limit your choices in bracing due to clearance issues.

20) On Skunk2's own head to head Dyno test, their 3 inch header only gained 4whp more then the RV6 header, not amazing, but more. I take that with a grain of salt, a lot of ways to manipulate info. When Skunk2 post their regular dyno numbers, they claim more or less 14whp gain. The RV6 actually had more than the Skunk2 at the lower band. RV6 dyno's and claims there gains at 13whp. BUT RV6 baselined the SI's they used at 150whp. The RV6 numbers were with their catless header version with no heat protection coating. With the coating a cat, maybe the about the same outcome. With the coating and no cat maybe the closes the gap 1whp or so...HAHA... BUT This independent dyno test (WITH KTUNER and DYNO TUNING), says Skunk2's 3 inch header gains 10whp (with tuning program, can't emphasize enough), with an SI that was baselined at 180whp (see link).

Revved Dyno Tech: Dropping Basic Mods On A 9th-Gen Honda Civic Si

Long (AS HELL) story short.... My opinion and recommendations are that 3 inch header and exhaust are most likely overkill for most anyone. Even for forced induction. They produce too much noise, take up too much room, reduce height clearance... Too many negatives over positives. 2.5 piping is probably a little under max power output. BUT - If you feel like going bigger with the piping, and going for max gain, go with 70mm/2.75/2.76 piping. There are several Civic SI 70mm exhaust options, and as far as I know (or could find) the one header option (so far) for this size is the Buddy Club Race Header. It's catless only. I've seen it online for as cheap as $300. Buddy Clubis a great quality, race proven brand. You may still need or want to get a rear motor mount with this.

If not, I'd recommend playing it safe and just getting an RV6 Header, 2.5 inch piping, in a ceramic coating finish. With or without a high flow cat, depending what you want. May want that rear motor mount still. Price point as pictured is $580.

I can provide Links to most everything I've discussed in this enormous post, feel free to ask where i got "X" info from. I did not post a ton of links mostly because they are from different 9th Gen Civic SI forums. No hate intended from this post. If you like what you're running, cool.

I live driving distance from Buddy Club USA and I think I'm gonna try to pick that race header up. IF that header fails or gives me any issues then, I will go for the RV6 as pictured (catted and coated). For me, it's a very close match up, but the fact that I'm pretty close to Buddy Club USA, means I can deal with possible issues in person. The fact that it's almost half the cost of the RV6 (in the style I'd get) doesn't hurt either.

Ok sorry about this but im also going to add a couple more posts. I have to break them up because for whatever reason, I've tried posting 3 times and Acurazine keeps logging me out... SMH

References - (to help you guys NOT make the same mistake that I did in purchasing a 3 inch downpipe)

First off, straight to the point Here is the Full Race 3 inch Down Pipe VitViper Dyno results. This is/was the downpipe that Vit was most recommending for people who want the most power gains. Keep in mind that the Buddy ClubDownpipe is a fairly new product.

"We netted as much as +10whp and +10wtq from simply installing the downpipe. That’s a sizable gain for a simple modification."

Now let’s throw a good tune on the car… and the results are as follows. Solid line is fully tuned, dashed line is our baseline with the downpipe installed. The tune netted as much as +12wtq in spots and as much as  +18whp on the top end."

Tested: Full Race Catless Downpipe for 2012+ Civic Si | VitTuned Blog

NOW - Here is the Buddy Club 2.75 inch header Vitviper dyno results.

" member slee0730, tuned & edyno'd with vit, here is his result with the dp

a bone stock civic si with buddy club 2.75 dp + vit tune = 191.29whp

BOTH Civic Si's baselined at 162WHP. And the tuned Buddy Club 2.75 Header made MORE power. Not much. Comparable/ same shit. BUT

Buddy Club Race Header can be had for as cheap as $300. I got mine for $311 out the door. The cheapest version of the Full Race Downpipe is $350. The Skunk2 is $360-$400+

Buddy Club killing the game.

OMFG I keep trying to post and Acurazine keeps EFFING up AGHHHHHH

Sorry... So These posts are going to be broken up because of some kind of technical issues... WTF

Straight to the point - 3inch downpipe gains vs the Buddy Club 2.75inch gains

This the dyno results for the Full Race 3inch Exhaust Tuned by Vit Viper. Both of the folowing dyno's used Civic Si's baselined at 162whp

First up, the Full Race 3 inch downpipe

We netted as much as +10whp and +10wtq from simply installing the downpipe. That’s a sizable gain for a simple modification.

Now let’s throw a good tune on the car… and the results are as follows. Solid line is fully tuned, dashed line is our baseline with the downpipe installed. The tune netted as much as +12wtq in spots and as much as +18whp on the top end.

What’s this look like over the original baseline before the downpipe was installed? Here you go. Netting almost +30whp in spots with a downpipe and tune on the top end. Sizable gains, the part worked well and the tune brought it all together."

Now Here's the Buddy Club 2.75 Race Header Results from Vitviper

" member slee0730, tuned & edyno'd with vit, here is his result with the dp

a bone stock civic si with buddy club 2.75 dp + vit tune = 191.29whp"

that means the buddy club was +29.29. Essentially the exact same shit guys. EXCEPT FOR

I got the Buddy Club Header for $311 out the door. The Full Race cheapest version is $350. The Skunk2 3inch header is $350-400+ And the Skunk2welds took a shit on me.

Buddy Club killing the Game. And 2.75inch for the win. Avoid the 3 inch pipes. The next post will show you WHY to avoid them

Here is the link to a 9th gen Civic SI WHO HAD THE EXACT SAME ISSUE. Busted at EXACTLY the same spot. Literally EXACTLY the same problem, on the same header. Flat out - it's a design flaw.

Interesting drive to work this morning.......Skunk2 Downpipe.

Here's another guy complaining about broken welds on Skunk2 headers, AFTER 1000 MILES!!! on a different application, and then others in the thread ALSO complaining.

Here is the Full Race 3inch Catback causing obnoxious noises by hitting the rack and pinion in the car. 9th Gen owner Metzger also had to remove Bracing bars because they made the problem (noise) worse.
One POSSIBLE fix to this is upgradiing the rear motor mount that costs roughly $150+S&H. Theres a link to the rear motor mount somewhere in that thread, in case you bought a 3 inch downpipe already.

ISSUE: Full-Race Catless DP hitting Rack and Pinion...

Here is a VitViper-Tuned and dyno'd, CT-E Supercharged 2014 Civic SI using a 2.5 inch RV6 downpipe, with no apparent issues at all, working perfectly fine. 3inch header, not used or needed, for Forced Induction. If you were to go Turbo, you wouldn't use any of these pipes anyway.

12 ? 15 Honda Civic Si | VitTuned Blog

*** If you scroll down on the link he also reviews the same Injen Cold air Intake I have. He says it heats up too much. this may be true. I have noticed in the summer, My MPG goes down. I now think it may be related to the CAI. I've noticed when it's cold, the CAI hits that VTEC AWESOME.
I'm going to look into getting the CAI piping Anti-heat Ceramic coated and wrapped with that "header wrap" heat wrap stuff. On Vit's Dyno blog, he says CAI help to gain about 5WHP while short rams appear to do squat.


Alright so... The Buddy Club Race Header I purchased is now installed.

Pro's and con's


Car runs/sounds smoother then with the Skunk2 header. The exhaust note is a bit quieter at idle and low RPM, but it is slightly deeper as well. The shift points are a bit smoother BUT, if you want to rev out and smash on it, it gets nice and loud, and its not "fart canon" at all.


Does not come with a defouler, you will have to purchase one or you will throw a "Check emission system" code. It will run without it on, it's just that you will have the annoying code showing. Costs maybe $50. HOWEVER, if you use Hondata or Ktuner, then you will be able to bypass the code without the defouler.

Does not clear the FKX Racing X brace. AND if you have any kind of bracing that cross's paths where the exhaust or downpipe runs the length of the car, they will most likely not clear. This is because of the position of where the exhaust hanger is welded onto the Race Header and also how the pipe ends up hanging. It ends up a little lower then the Skunk2 pipe, and also has less angles in the piping, it uses longer curves to create straighter piping, to create better flow.

This race bracing bummer I know is not really gonna affect most people because most ILX drivers are not serious tuners.

This a bummer for me tho, (I'd consider myself a casual tuner). I like stiffening up the chassis/frame/suspension overall, in a way so that it is spread out, and not putting too much stress on any one specific piece or area. I believe that's a simple way to avoid issues like subframe tear out and broken end links on sway bars (especially the rear) from aggressive driving. Eventually, as my ILX gets older, and as I eventually get another car as well, I could definitely see myself taking it to the track for fun. To people who think these bars do nothing, I can actually hear the front lower tie bar squeaking a little bit now, because there is more stress on it now without the X bar. I didn't notice a drastic change without the X bar, but I did notice a little change. The bigger improvement effect comes from the overall addition of different upgrades. I plan on getting the Eibach front sway bar to help the front end out a bit more, and then a trunk brace for the rear. There is a couple other bars I may get to finish off the handling upgrade effect. At least one other bar I was looking at getting, I know will not clear the exhaustpiping either. The middle lower bar.

If you get any suspension bars (other then maybe the sway bars) it's kind of normal to hear a little squeaking as they work there little "ass groove" in, and kind of settle in. Then you just have to make sure the bars are really tightly bolted in, and it should stop.

So yesterday I was talking with a group of 9th gen Civic SI enthusiasts, and most of them were telling me they actually prefer the 2.5 inch and 2.75 inch piping exhausts and downpipes much more as well.

My mechanic also told me about another issue from the 3 inch piping. There are a few bolts that stick out a little where the exhaust path runs. Exhausts tend to have a bit of freedom of movement and also take a couple hits on speed bumps. The 3inch piping was hitting the bolts and getting damaged and making annoying noises, he had to manipulate/bang around on the pipe to make it clear the bolts. This won't be an issue with the Buddy Club Header as it pushes the piping a little further away from the undercarrriage. Avoid the 3 inch piping guys.

I also was considering getting header wrap on the Buddy Club downpipe, but decided against it due to it possibly coming off or catching on something because it sits a bit lower then the Skunk2. Also the piping itself is VERY close in sizing to the 3 inch, which explains why it sounds similar, but better, and has the same exact gains. I thought it would hug closer to the car, but it doesn't.

So in summary - go Buddy Club if you want max gain at cheapest price point with least issues, and if you don't care about bar clearance.


I think if you go RV6 2.5 inch downpipe with ceramic coating, AND header wrap it, you should be able to add/clear the braces, clear other stuff, AND have a NICE Downpipe setup that will be a little quieter, yet tiny bit deeper, AND I bet would get the same gain (maybe even tiny bit better) as a 3 or 2.75 pipe. This I feel would REALLY be the best setup, albeit the most expensive. If the Buddy Club breaks on me, I WILL get this setup.


K24ILX, pretty sure thats because the Fullrace Downpipe seems to have a better overall design (IMO) compared to the Skunk2.

Here's why:

The Full Race Downpipe Bellmouth piece attaches immediately to the Flex pipe section. This is where the most severe angle is in the piping, so IMO, where the pipe is most likely to break/bust due to engine torque flexing. They went with a smaller flex portion as well, probably better for back pressure. The people hearing MORE rattling noises and such, PROBABLY went with the catted version, which as you can see in the pics, makes the pipe pretty fat in that section. Everyone's mileage will vary. The only downsides I was able to find online about the Full race header was unwanted noise. Which appeared to be able to be remedied with an upgraded stiffer rear engine mount. Which is something I will be looking at doing myself.

Again, just shows that the Skunk2 downpipe is not the best one
available for this application, for several reasons.

Right now, since it's winter and the Buddy Club Header is breaking in, I can hear it's getting louder. Noticeably so. The air is denser and sound carries more, but I can tell it's not just that. My sister even commented on it when I gave her a ride. I just got new tires and that also increased road noise, as they are ultra high performance. But it also increased performance a lot, which means I've been pushing it more, so the header has been putting it down to the wheels more. They fed off of each other.

No one way to skin a cat, just making people aware of possible ups and downsides.

The Buddy Club header hits harder IMO then the skunk2, especially with my new wheels. As in, more performance and better sound. It sounds cleaner, deeper and louder

However, I did notice MPG went down a little. This may be partly due to it's breaking in and the ECU is still catching up. Without the X-frame brace stiffening up the front mid-frame, the front lower strut bar is taking on more of the job.

Since I got better tires and I'm having fun and pushing it a bit, the front strut bar is squeaking a little. A bit annoying. I know what it is, but passengers don't, so that's always very annoying trying to explain.

I need new rear brakes. I bought new from Buddy Club race spec, regular $85, got them for $35. Gonna get those replaced tomorrow and have them tighten that down and see if anything else is going on. They are probably a bit louder then stock, as long as it's nothing crazy loud, I'll be good. I personally don't mind the car being a bit louder overall, but I dislike drawing the unwanted attention of law enforcement.

Cabin noise can be an issue on a long drive as well. It's not crazy bad, but it's a lot louder then stock. I'm definitely going to look into getting some sound dampening material for better stock radio sound, heat/cold, and noise control.

Again, realize the overall effects from mods guys.