Anyone who wishes to fabricate manifolds of any kind will need to purchase (sometimes upwards of $400 each) or build collectors. They are very expensive for quality pieces, with the right tools and time anyone can make their own quality merge collectors.
Tools you will need:
Welder
Cutting device
Protractor
Scribe and or pens
Measuring instruments
files
Safety gear consisting of at least eye protection (I wear a mask and ear protection when cutting)
Supporting tools for your equipment
First you must select your material, for every turbo manifold I build; I use 304 stainless steel sch 10 which is readily available from many places. I get mine from Ace Stainless, I highly recommend them. For basically all Audi/VW applications I use 1.5" primaries. As this material is a nice match to exhaust port sizes at hand. You will need approx. 6 inches of material for each individual runner, so for two 3-1 collectors you will need at least 3 feet. Get yourself double that, you will screw up and you will need a bunch for other stuff anyway. tip, go get some sch 10 1.5” pvc as it shares dimensions, good for practicing at a fraction of the cost.
Choose your cutting method, I have used chop saws, band saws, mills and even seen them cut out with a cnc plasma. I use a chop saw because it is cheap, easy and discs are always available. The concept of all of this is the same on any machine. Now you need a jig/clamp of some sort, no saw of this type will have a clamp that can reach the extreme angles needed here. This is mine, it technically isn’t a jig because you still have to measure length and set angle for each cut, but I like it, I am use to it and it works.
Materials are simple, 2” sch 10 pipe (I used ss because I had it at the time, I suggest cheaper mild steel for this) with a piece of angle iron welded on and bolted to the saw bed. You can also see I utilized an existing hole on the saws bracket for further strength, welded a bolt from the inside and ground down. To clamp I just welded a nut to the top after drilling the proper size hole and run a bolt in. It is set at 11.5 degrees for my intersection angle. I make all my collectors at that, the less angle, the more flow, but also more length. You can make a more compact collector by going to higher angles, but that takes away smoothness. It’s all a trade off. Adjust for your application and needs. I make things geared towards max power, not always ease of install or practicality.
In these pictures you can see I threw some tacks into the lower sections of the tube, this allows the piece being cut to always center to the same position horizontally as the bolt tightens. Do not make them so big as they keep the tube from going flat on the bottom of the clamp, you can fine tune this with a file.
Set the depth, I use 6 inches as that’s what works perfect on this setup. Since I have not said this yet in this article, Measure twice, cut once. Save yourself the hassle in life, always measure twice, cut once. edit: I noticed I forgot to mention a key thing here, your two cuts have to be at the exact same depth, not exactly my depth of 6 inches, just the same depth for each set of two cuts. Otherwise they will be off and wont mate up to other collectors. This is one of the most important measurements in the process.
Then you need to mark a reference point, I like to blacken an area with a sharpie, then scribe over that, makes it highly visible with glasses and all that.
Now you must get your base angle off your blade, all cuts are based off the actual thing doing the cutting. Do not make the easy mistake of just marking out X amount of degrees on the tube and removing everything else thinking it will make a circle. Due to the fact the angled cuts are what eventually need to come back to 360 degrees you will be way off. I am lucky and my garage is flat, bench is square and my saw is true. My blade sits at dead nuts 90. If yours is off that is okay, just adjust everything to match or shim your saw base accordingly.
Then you need to dial your tube in to the same spot which is now 0. On this simple magnetic protractor I modified it a little, I made a slug of hot glue on the back to make it stick into tubes easily and stay. I can run a long stick through and cut out 6 collectors without it ever budging. They probably make one like that, I have had this one forever and it was like 10 bucks so I just made it better.
Now you are ready to cut, you have some options here. You can go +/- 30 degrees from 0, or you can cut there and then roll a full 60 degrees to the right. I do it both ways, I don’t know why. It’s not easier or harder either way. I will detail going +/-30 as it is more accurate for most beginners I think. On my saw I actually go to +/-31 degrees, every setup will vary ever so slightly from many factors such as blade deflection so I will always make reference to it as a flat 30. The 30 is for doing 3-1 collectors. Other styles such as 4-1, 5-1, 6-1 and so on will each need different amounts removed. The 30 stays the same regardless of that intersection angle from earlier.
Make that first cut, I pulse the blade slowly until I make my first little groove to lock into as chop saw blade likes to flop around a bit. I have found this works with a very high level of precision compared to just squeezing the trigger and hammering down. When finished it should look something like that. You can run the saw up and down a bunch after finishing the cut to face the piece and reduce finish work you will need to perform.
Now roll back past 0 and go 30 the other way for your second cut. I should mention you can reverse the order to suit your preference; you don’t have to do either cut first. I like making the ghost cut as it is a flat surface. Face this cut just like the last to reduce hand finishing.
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