How TO: Build a merge pipe
 

A little tutorial on how to make a simple merge pipe with basic tools. All the tools used are are:

Bucket of water that your length of pipe can fit in long ways
Food coloring
Sharpie
Hand File(half round)
4.5" Milwaulkee angle grinder with a cutoff disc and a 60 grit flap disc
Paper towels
Welder of your choice
Posterboard/cardboard and scissors

http://img434.imageshack.us/img434/8943/dp0013ck.jpg

For materials, buy some flowmaster header reducer cones, part # R3530. Heres a link to summit:
http://store.summitracing.com/partde...5&autoview=sku
The goal here is to make a single 3.5" downpipe split into two 3" exhaust pipes. This method will work for any pipe sizes/transitions, even just using two pieces of straight pipe to make a merge, such as single 2.5" into dual 2.5" for a header crossover. As long as what you're merging is symmetrical, this will work.

One note before we get started, I don't know how well this will work on different materials. It seems like it doesn't work so well on rough surfaces, the food coloring seems to seep in and not wash off nicely. I used aluminized exhaust tubing, which is very smooth and clean, and it worked extremely well. If it isn't working on the piece of metal you're using, perhaps try waxing the piece to get a smooth finish.

Lets get started!
Start by marking the centerline of one of the pipes on the end which is going to be the single part of the merge - the 3.5" side in my case. Mark on the inside and the outside! Makes it much easier to see.

http://img314.imageshack.us/img314/9538/dp0020pi.jpg

Now, put a drop of food coloring on the pipe near one of your c/l marks. I used the darkest color in my food coloring set, which is blue. It still didn't come out very dark, so I somewhat doubt yellow or red would work very well. Just pick the darkest that you have.

http://img314.imageshack.us/img314/9760/dp0033se.jpg

Now, use a folded up paper towel to smear the food coloring around on the pipe. Keep working it until any bubbles of liquid are gone, just colored pipe left. The paper towel will soak up a lot of the first drop or two, consecutive drops will go a lot further. You can also use the towel like a felt marker after a few. It only took me 3 drops to color nearly half of the pipe, which is more than enough.

http://img314.imageshack.us/img314/7109/dp0040va.jpg

Make a 'U' shape going from one centerline to the other, and touching the opposite edge at the bottom of the U. Here you can see half of the U. It doesn't seem very dark, but it still shows up well.

http://img314.imageshack.us/img314/9508/dp0059wo.jpg

Now the tricky part. Hold your pipe sideways by the edges, so your centerline marks are parallel to the ground. If your finger holding the pipe is 12 o'clock, your centerline marks should be 3 and 9 o'clock. Very carefully lower your pipe into your bucket of water to the centerline marks of your pipe, and approximately 3/4's of the way down the pipe. You have to be very steady and pay attention to all sides of your pipe at once. I find its easiest to first lower your centerline marked side into the water at a steep angle(like a 60* angle, so very little of the pipe is submerged), then hold that side steady and slowly lower the angle of the pipe with your other hand until you get 3/4s of the length of the pipe submerged. Hard to explain, but you should understand with some pictures...

Fresh out of the water.. this one I messed up as you can tell...

http://img252.imageshack.us/img252/5154/dp0060gu.jpg

Once you get it out of the water, carefully blot the drips off, do not wipe! Keep the pipe in the same position it was in the water otherwise the drops will run across the pipe and ruin the line. Once it is dry, it should look like this:

http://img252.imageshack.us/img252/1144/dp0077od.jpg
http://img252.imageshack.us/img252/1492/dp0081we.jpg

Although it isn't the easiest thing in the world to get the perfect line, it is extremely easy to re-do it! If you mess up, just wipe the water off, add a drop of food coloring and recolor it. It takes 30 seconds to color it. I did it 3 times before I got a line I was happy with. Still only took me 3 minutes to do.

Now, our line is there and fairly visible, but it isn't near dark enough for me to see while grinding on it. So I took a sharpie and traced the line very carefully. Sorry, don't have a picture of that...

I then took my grinder with a cutoff wheel and started cutting. I cut each side down from my centerline marks to about 1" from the bottom of the U, where it gets real tight. Too tight to make the curve with the cutoff wheel straight up. For the bottom of the U, I lay the grinder down almost parallel with the pipe and make the cut. When making a cut like this your cut line gets VERY wide, so don't just leave room for a kerf that is the thickness of the blade! I cut so the tip of my wheel was about 1/4" in from the line(that I could see) and when I was done, the cut was just about right on the line.
Here is how pipe #1 looked after being cut, laid on the ground to check for flatness:

http://img252.imageshack.us/img252/8601/dp0094xf.jpg

Not bad, I messed up the top a little bit. I think what I did is when I rocked the piece in the water to get the line for the bottom of the U, I accidentally lifted the top about 1/8", giving a slightly curved line. Nothing a little grinding can't fix.

http://img304.imageshack.us/img304/3006/dp0107cb.jpg

The other side is a bit better. Just a little work to do here.

Use your file to fine tune and deburr the edges. Over the past few months I've grown to love my hand files, they're now an everyday tool for me.

Unfortunately, I got lazy with taking pictures so there aren't any for this section. Its pretty simple, though. I'll get some pics of my templates in a few.
Now that side #1 is completed, we can move on to the other side. In order to get a perfect mirror image, use a piece of cardboard to get the imprint of the cut line. I used posterboard, which is somewhat flimsy. I'd use corrugated cardboard in the future. Put the cut pipe in a clamp with the cut side up. Place your posterboard/cardboard on top of it, and press down with your fingers to trace the cut edge. Remove the cardboard, and mark with a sharpie the top two corners. Use your scissors to cut along the imprinted line, flaring outwards once you get to your edge marks.

Now, lay this template over your second, uncut piece. Line up the edge sharpie marks you made with the top of the pipe. Position it so it has no gaps anywhere around the cardboard. Try to keep it perfectly flat. If you cut well it should lay on there perfectly. Hold it in place and trace around it with your sharpie(a fine point sharpie works best for this). Cut it to the outside of the sharpie line using the same method as #1. Fine tune with a flap disk and files. In the end they should look like this:

http://img304.imageshack.us/img304/8320/dp0116el.jpg

And there ya go, one perfect merge for $25 and about an hour of work!


Credit go's to TomServo, not me.

That's a fantastic idea. I've eyed it up and used a belt sander to perfect it but this is great for a guy with just a cutoff wheel.

Another way is to use a laser level, line it up, mark it with a sharpie, then cut away!

Good thread, thanks Viking.

in any after or on the car pics]
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Well done man. how is the fit on the inlet side? since once the cuts are made to about a half round shape im just curious as to how well it mates up to the inlet side for welding? I ordered my pipes today. think im gonna do a dual on my FB coming out right before the rear tires.

It's a perfect round fitment on the inlet side. I'd post pictures but my welding sucks, I ended up sending mine to A-Spec so that they could build me a good manifold.