Honda Civic Forum - The ultimate DX/LX vs EX header/exhaust DIY and FAQ

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The ultimate DX/LX vs EX header/exhaust DIY and FAQ

Ask me your questions DX/LX header/exhaust questions!!!
This will be updated as information is needed.

First many people with DX/LX’s want to know what header will work.
First, the EX header wont bolt up to your existing stock exhaust. Second, you WILL loose your cat. Here are your header options if your cool with your peashooter exhaust and no cat:
Kamakazi – part number: ??
OBX – part number: 10-1602-3D

Will an EX header bolt up to the head of an DX/LX engine?
Yes, the bolt pattern on both the D17a1 (DX/LX) and D17a2 (EX) are the same.

So I should be all good right?
No. Just because the header connects to the head, doesn’t mean the other end of the exhaust has matched up- and let me tell you, it doesn’t. The LX header connects at a point several inches lower then the EX header does to the rest of the exhaust.

So what can I do?
You need to find some way to connect it. You have three options:

If you want an EX header and stock DX/LX exhaust w/o cat, then take it to a muffler shop and have them custom weld the two together. You will loose your cat of course, and you'll have to stare at the check engine light every time you drive your car because the sensors wont be taking readings they understand. To avoid this- see O2 extenders / defoulers.
If you want an EX header and stock DX/LX exhaust with a cat, buy a cat and take it to a muffler shop and they will connect the header to the rest of the exhaust and weld the cat in line. This is kind of stupid- see backpressure. You'll also run a check engine light. To avoid this- see O2 extenders / defoulers.
If you want an EX header, and an aftermarket exhaust you have two options.

Buy a stock EX downpipe to connect to the EX header, along with some O2 sensor extension cables or defoulers. Specs: It starts off with an internal diameter (ID) of 2.00" and tapers down to 1.70" ID, finishing with an exit ID of 1.85". This is what I consider the best option if you want to avoid buying the RT downpipe (see below).
Buy the Random-Tech downpipe from Dezod to connect to the EX header, along with some 02 sensor extension cables or defoulers. This is the best option if you cant find a EX downpipe.

What is a cat back?
Essentially this is a full exhaust from the cat converter in the downpipe on back, including the muffler, and usually includes an inline resonator as well.

What is a downpipe?
The pipe that connects the end of the header to the rest of the exhaust. This will have a cat in it. If there is no cat, it is called a test pipe- these are usually reserved for turbo applications.

Where can I get 02 extension cables?
This is where I got mine: Casper Electronics. (some reason I cant directly link you- go to the site, click on honda on the left, and your get three dif size options for O2 extention cables) I purchased a 24-inch, and a 12-inch because there are two sensors. While I wasn’t able to, I have been told that some have been able to connect one of the first O2 sensors without the 12-inch extender cable. If you want to splice in wire to lengthen the cables thats up to you, but its creates the potential for more things to go wrong, plus the O2 sensor has a specific voltage so a change in resistance can trigger a CEL. I've also found O2 extension cables here: PasswordJDM or Club RSX

Defoulers
First off lets explain the two O2 sensors. The primary is prior to the cat and exists for air/fuel into. The secondary is after the cat and reads for a working catalyst. A defouler pulls your sensor (usually only need this for the secondary) out of the exhaust stream. This is used by people running race headers with out cats, or cats that are non-functioning. With a defouler, your ecu will not throw a CEL (check engine light). Two options are available- straight or angled. With an angled defouler the sensor will pick up less of a signal and may save you from needed an O2 extension cable under certain circumstances. For more info on how-to, check this out: https://www.civicforums.com/forums/7...simulator.html

Will an EX’s exhaust hangers need to me modified in order for them to hang from my DX/LX points?
No. Thankfully no hanger bending is required at all when putting an EX exhaust on your DX/LX. Even the original rubber donut’s are reused.

Hold on, this is going to get technical for a second

Backpressure
Backpressure is basically some sort of restriction on the air volume/exhaust coming out. A good exhaust system has the right amount of backpressure. Imagine if nobody ran an exhaust system- everyone’s car would be super loud and also yield more performance right? Wrong- they would actually loose power due to no back pressure- that’s why exhausts are important tricky little bastards.

With more backpressure, you’ll have better bottom end (this means you’ll be able to accelerate better at low RPM’s). More bottom end is best if your staying away from the track and the strip and not driving like an idiot, or if you just want good fuel efficiency why driving in the city driving.
With less backpressure you sacrifice bottom end for top end power. This is best if your on the track most of the time. This is best if your on the track most of the time and need power at high RPM’s.

Exploring the stock downpipe
The stock downpipe seems like its 2.25 inches thick, but its really not because its double walled which gives it the appearance that its bigger then it really is. I believe I measured it at 1.75” when I did my swap.

Whats the best exhaust diamater?
A lot of people say the max they would go with out having extensive motor work done is 2.25”, which others will say that 2” is best. The theory behind saying that 2” is best is that its .25” larger then the downpipe, which should be more then efficient.
The whole thing with exhausts is to not bother increasing one section of pipe unless the others after it are increased as well. You don’t want to have a large downpipe that goes to a small mid pipe, then to a huge muffler with a 5-inch tip. The fact is your exhaust will only be as efficient as the smallest. It’s a thin line, and without dyno sheets for both size exhausts from the same car that are tested in the same conditions, there really isn’t any factual proof that I can give you that can back this up.

Sectional exhaust piping
The sectional piping are pretty similar no matter what exhaust system your looking at, size is the only difference. Exhaust systems tend to be much louder without a cat then system with a cat. To counter act this you can purchase a silencer that sits inside the muffler outlet to restrict the sounds but can/will also restrict the air coming out. Regardless if you choose to run a silencer or not, you’re going to be polluting the earth like crazy.

“Whoa cool, a packaged deal!!”
There are a few setups offered as “packaged deals” or “all in ones.” Be weary. Many of them leave you with out a cat converter. You might be tricked to thinking there is one in the system your looking at because the manufacturers like to place a resonator in the place where the cat would traditionally go to trick you. These are called test pipe.

Conclusion
So… in conclusion don’t worry about a 2.5” exhaust unless your boosting or you figure out how to do some seriously amazing NA work. You will be ok with 2.25” piping, that’s what I have- but that’s the max I’d go with. With 2” you’ll be good and will have a little more bottom end, although you’ll get a increase in top end from the stock exhaust but also a hardly noticeable decrease in top end from what your would experience with a 2.25”. Being I am running a 1.75” to a 2.25” I can say that you’ll be fine, although I think you might get better performance if you had a 2” pipe the rest of the way back.

Additional notes:
The DX/LX exhaust has spring loaded bolts that connect the end of the header to the rest of the exhaust system; these are kind of a pain in the butt to reach but they come off eventually.

If your having trouble getting the exhaust hangers out of the rubber donuts, use a little lube that’s not corrosive to rubber, like white lithium grease that you can pick up at Napa like shops.

Jack your car up and get it on 4 jack stands so you can slide under the entire car with out any problems. Double check that the car is jacked correctly so that you don’t crush yourself.

Use extreme caution when loosening the header from the head of the engine. Use a crisscross loosening patter to prevent warping. Do not loosen one nut all the way, and move to the next, this is horrible for your head. If your having trouble loosening the nuts (which was my case), tap/hit the end of the wrench with a hammer. This is a lot better then using all your might to loosen the nuts- I cracked several sockets when trying to muscle it.

Removing your cat is illegal in most states. Also in some others modifying your exhaust is as well. Check your states requirements, before proceeding.

Questions answered:
I keep hearing that you do need an EX sway bar if you're doing an LX to EX exhaust swap, and i hear that you dont. Im doing the cat back, header, and hi-flow cat--will i need one?
You will if you are going to be using the stock cat.. but I couldnt tell you about the high flow cat- I know they are thinner so it might work, but I dont know if they are thin enough. Only way to find out is if you go and do it... if it doesnt fit, then you just need to get an ex sway or an rsx sway.

For you 8th Gen guys
This is all I got for ya. Thank FGcoupe:

On models 06-07' there is no header to mount onto the cylinder head,
instead they have changed this design using an integrated exhaust manifold.
So, this is a single 2.5" pipe with the 2-bed CAT (Closed couple catalytic converter) as part of it. You cannot remove the CAT material but other alternatives would be to purchase the WeaponR downpipe which in this case removes the CAT all together and uses a defouler to trick the CEL.

Midpipe-This is the section of piping that connects the exhaust to the CAT,
Megan Racing has a mandrel bent section to improve flow. This is bolted
to exhaust manifold with x2 springs/bolts.