Evo IV CN9A to Evo V CP9A Arches (Wide Body)

Submitted by Slowboi - Aaron W. on Mon, 02/26/2018 - 11:20

How to cut your rear arches back for bigger tires.

Everyone wants wider tires! If you are the owner of an Evo 4 unfortunately you have a narrow arch car.
I've owned several Evo 4’s and throughout the different stages of modding them I eventually end up cutting the rear arches.
With these modifications you can fit up to a 265 tire using the Evo 5/6 stock over-fenders with an intelligent wheel choice.

First be sure that you have, or can borrow the following tools, otherwise this will be painfully slow or you will damage something using the wrong tool for the job:

- Air powered rotary cut off tool
- Mig welder or a welded suitable to weld body metal
- Body hammer
- Various metal files
- Some pics and sandpaper
- Drill bits and a drill
- Etch primer
- Seam sealer
- Green masking tape
- Vice grips
- Grinding tool to dress welds

Before I start, let me preface this by saying there are many ways to do this, this is my way and obviously there are other ways.
So if you are uncomfortable with my methods, then ask around, and maybe do something another way.
Totally up to you, because it's your car! I will take no responsibility if you burn your car to the ground welding or mangle your arches.
Know your skill level! Read this front to back and if this is beyond what you can do, call a shop.

Keep in mind if you use the Evo 5 flairs you will have to use the Evo 5 skirts, and the Evo 5 rear bumper.
Follow the link to our Facebook video discussing body work options on an Evo 4 to 5 conversion:

"Talking about the Evo IV wide body."

Step 1

You need to decide how much of the rear arch you want to cut away. I usually cut the arch back to approximately 1cm remaining before the bend that goes into the door frame. It is important to leave some metal as you will be welding the two sheets of metal that make up the wheel house, back to the external body panel. This is important to maintain body rigidity. So cut an arc out of the arch leaving 1cm until the door gap. Do not cut off the mounting point for the rear bumper.

Step 2

When you cut, use several shallow passes with the cut off tool. You only need to cut the outer sheet metal. You want to have extra available on the inner metal to be able to fold it over later.

Step 3

Use sand paper to sand back the edge of the cut to allow bare metal to show. You need clean metal to weld to. I usually sand the paint back about 4-5 mm to allow a good clean arc to be produced by the welder.

Step 4

Using a pic with a hooked end, insert it between the two pieces of sheet metal the full length of the arch. You should be pulling out some grey foam. Get rid of this foam as it will likely burn during welding.

Step 5

With the same pic, insert it between the sheet metal to give you some room and insert some 150grit sand paper between the sheets of metal to give a nice clean inner lip. This will be important when we spot weld.

Step 6

From where the door seam ends to the front of the car, use a 1/8 drill bit to drill holes every 3cm. From the door seam forward we will be spot welding, from the door seam back we will be folding and trimming the arch and welding the edge.

Step 7

Start welding by using vice grips to hold the inner and outer metal together, then tack weld through the hole you drilled. Dress the welds as you go with a grinding tool.

Step 8

When you have completed from the door seam forward, using your body hammer, lightly tap and fold the inner wheel house to the edge of the outer arch. Weld every 3cm and trim to fit. This part takes some patience so take your time and go an inch at a time.

Step 9

Tape off the car and after suitably cleaning the metal and dressing the welds, etch prime the metal. Let the primer cure. Then seam seal the entire area.