Make your own intake for the VTX 1800

Information courtesy of Duc from the VTXOA

Preface
This is a basic walk-through for building your own intake for the VTX 1800. Duc from the VTXOA is the original person who came up with this idea, this write-up is based on his idea and just expanded a bit with info from my previous write-ups. In Duc's own words - "If you are mechanically competent this is an easy build".
I would also like to add - please do not send me a ton of emails asking how to cut and drill these pieces. Look at the pics, evaluate the tools you have at your disposal to do the cutting. If you can't figure how to do it on your own or don't have the tools necessary then perhaps this isn't the project for you.
Now for my boilerplate disclaimer - undertake this project at your own risk!

If you haven't done the desmog let me recommend doing it - feel free to read that write-up and decide on your own, but if you have the smog setup still on the bike you'll have to find some way to deal with the PAIR inlet since this project is written for a bike without smog equipment.

Preparation/supplies

Stock intake - buy one in the VTXOA classifieds or cut up your own

K&N filter assembly #56-1080

Pre-filter for K&N E-3341 filter (optional)

K&N crankcase filter #62-1010 or 4 feet of 1/2" rubber hose (vacuum hose from any auto parts store works fine)

Philips screwdriver

2 small nuts/bolts/washers for reinstalling the IAT sensor

Drill and drill bits (various sizes)

Various metalworking tools, depending on what you have you can use anything from tin snips to a dremel - evaluate what you need to do and make your own decisions

If you're removing the stock airbox you'll need:

5mm allen

possibly an impact driver

Look around online for the parts you need, try googling the filters and just buy them from the cheapest seller. The pre-filter is an optional thing if you're concerned about riding in the rain, however I've never seen fit to use one when I ride in the rain and I've never had a problem. K&N filters are oiled, so they naturally repel some water to begin with and a little water in the motor is not going to hurt anything.

Removing the stock airbox
If you're not removing the stock airbox you can skip down to the next section, if you are removing the stock intake then follow the steps listed here:

Remove the stock airbox cover and filter using the 5mm allen.

Remove the 4 screws that hold on the plastic velocity stacks and air box "back". If they stick use an impact driver rather than strip the screws - just be careful when you hit the driver, you just need a little tap with a hammer the driver does all the work. Remove the velocity stacks.

Now let's remove the seat by pulling these 3 bolts:

Now remove the 3 5mm bolts closest to the seat on the dash and take off the gas cap. Be careful to not lose the plastic washers behind these screws as well.

NOTE: Leave the gas cap on until you get all the screws out and away from
the dash - it is very common for people to drop the screws IN the gas tank during this step!
To remove the dash panel slide it forward a little and put the gas cap back on the tank. Be careful not to lose the little rubber piece that the dash slides onto on the tab on the front of the tank. Wrap the dash in a towel to protect it and lay it somewhere out of the way. Brace the front wheel/forks/handlebars so the bars won't flop around and ding the tank, and as a failsafe lay a heavy towel on top of the tank to help protect it in case something does hit it. With that done you'll see the 10mm nut/bolt that holds the tank to the frame down where the seat was. Remove that bolt and you can either prop the tank using Biglry's tank prop:

or lift and slide the tank back about 4" and lean it over at about a 45 degree angle to left side of frame (it will sit there just fine).
Now if you start to pull the airbox away from the bike you will see 2 hoses and an electrical plug going to the back of the box and one small vacuum line plugged into the flapper valve at the top of the airbox (unless you've desmogged then you're missing the PAIR inlet and flapper valve). Reach behind the airbox and pull off all the hoses and the electrical plug. The plug has a little tab you need to press to get it off. With this removed you should be able to get the airbox off the bike altogether.

Crankcase breather
This is a personal decision you'll need to make before installing the new intake you're making. The new intake will not have a port to plug the crankcase breather hose into, so you'll either need a filter like the one I mentioned above (#62-1010) or you can use the 4 feet of vacuum hose to reroute the crank breather under the bike (unfiltered). If you choose to use the K&N crankcase filter you can install it by slipping the filter nipple through the old lower airbox mounting tab and then attaching the crankcase breather hose. You can see it mounted like this under the new intake in this picture:

If you choose to run without the crankcase filter then take the 4 feet of 1/2" vacuum hose and replace the existing breather hose. Trace the old hose to the top of the front cylinder (left side), remove the original hose and run the new one from the top of the cylinder down the backbone of the bike and under the seat so it exits under the bike in front of the rear tire. This will be behind the coolant reservoir or your fuel pump depending on what year/model VTX you have. You should be able to see the other (much smaller) overflow vent for the fuel tank in this same area.
Some people will tell you not to do it this way because the crankcase needs filtered air and/or something could possibly clog the line, but to quote Duc:

"I have had mine this way for 50,000+ miles and have done 3 other bikes the same way without a problem. Now I'm not saying you won't have a problem, but I am saying this is how it was done on bikes for YEARS. If you're concerned about it then blow air through it when you do a valve adjustment (every 8k miles) for peace of mind."

At this point you should be able to reinstall the tank, dash, seat, etc just by reversing the steps above in the first section. Installing the new intake can be done without the tank raised.

Making the intake
This is where things get a little more "do-it-yourself". Duc's original write-up and pics are a little more basic than what most visitors to my site are used to, so look at the pics below and walk yourself through the process.

Take the K&N filter assembly (#56-1080) and your stock intake "back" and cut/drill them up so you have this:

You'll have to drill holes in the K&N backing plate for the 4 velocity stack screws to pass through as well as 3 holes for the IAT sensor (sensor and 2 mounting screws). My best advice is to cut a little and test fit, cut a little more and test fit until you have what you need. You can always cut more off but you can't add if you cut too much.
The black looking "stuff" on the K&N backing plate is black paint used to prevent rust. The silver looking tape is metal duct tape (like is used for sealing A/C ductwork) used to cover a hole drilled by mistake and two holes that were already in the backing plate. If you don't have this type of tape you can use any number of possible solutions for these holes such as JB Weld or silicone sealant, the important thing is to find something that will seal the holes and never come off. This is an area inside the filter element, so if you use something that eventually comes off it will get sucked into your motor - this would be bad!

With everything cut, drilled, sealed, etc install the IAT sensor into the modified K&N backing plate and plug it back into the bike. You'll need to get 2 small nuts/bolts and possibly washers to mount the IAT sensor to the backing plate.
We'll be installing everything back onto the throttle body:

Place the K&N backing plate against the throttle body, on top of that place the cut down section of the stock intake, and then secure all that in place using the stock velocity stacks with it's 4 philips screws. Do not reinstall these with the impact driver, just use a #2 philips screwdriver.
With all this in place you just need to install the K&N filter element and the top plate so you end up with this:

Now get out and ride it!

Afterthoughts
This is a GREAT mod designed for those riders who are "do-it-yourselfers". The overall cost for this project should be between $50 and $100 if you shop around for decent prices on the parts. There is really no difference between this intake and many of the oval aftermarket units that are out there and cost a LOT more. Lots of riders have done this mod thanks to Duc's original write-up, and since Duc lost his hosting for it I offered to put it up here. This mod shows that a little thought mixed with planning and elbow-grease can save you a bunch of money on a pretty neat intake!
I don't have dyno sheets on this intake, but I can tell you that similar oval intakes like the Xtreme Revolutions version and the older CDS model have generally been regarded as some of the better units available out there for the VTX.
Duc is the original creator of this project and has said he is more than happy to answer emails concerning the process. There are also several pages discussing this project on the VTXOA under "1800 tech".