Sometime last year, I started to hear voices in my head. "The 16G turbo is ancient technology" they said. Then it was "you are leaving power on the table with your old log manifold". It continued, "internal wastegates are for pussies", "grow some ball bearings", and so on. I couldn't take it anymore, so I decided to build a tuned, tubular, equal length, 4 into 2 runner manifold with a twin-entry Garrett GT3071 turbo and divided, external wastegate.

The only problems are I have never designed a manifold, I don't have any 3D CAD software, and I don't know how to weld. I scoured the net and text books for month and came up with enough formulas to determine runner sizes and lengths (1.682" ID primaries, 2.210" ID secondaries, and 28.9" from head to turbo). Then, I borrowed SolidWorks '05 software and learned how to use it. I created each component and positioned them to match the available space and my earlier calculations. Lastly, I watched a sanitary welder at my work for about 20 minutes and started practicing what I saw on the company TIG machine.

Now for the disclaimer:
I still don't know much about designing manifolds
I am still a C average CAD designer
I am still a C- TIG welder
Follow my example and your car will burst into flames, killing you in the process!

Let the journey begin:



I lived and breathed SolidWorks from December to February.




I designed the head flange using a spare 2GNT head I just happened to have lying around. I designed the turbo and wastegate flanges from the Christmas presents I bought myself. The flow length of the runners is equal to within 2 mm “in theory”.




I obtained a plate of 304L SS and had a shop CNC the flanges out. By the way, I had a few extra cut, so watch the For Sale forum.




After about a month of dick dancing, burning flesh, and an angry wife, I have everything tacked together for test fitting. Everything is 304L SS, 0.109” wall pipe. Note the numbers to indicate location and lines to indicate orientation.




I didn’t take pictures of it, mostly to block the horror from my mind, but I made steel dies to form every transition. With a torch and die, I was able to form the “head to primary” transition, “secondary to turbo” transition, and the collectors. Without a doubt, the eccentric taper and “D” shaped turbo inlet of the “secondary to turbo” transition was the worst. Scratch that. Making the second one mirror the first was the worst part.




These were some of my first welds. My skills were comparable to Ray Charles on Ephedra. I did back-purge with argon and inspect the interior for full penetration. I overheated the weld, didn’t clean the joint well enough, sucked at welding, etc.




The #2 & 3 collector weld shows some improvement.




That #1 & 4 collector can kiss my ass. Most of those welds are ugly. You can see the divided external wastegate mocked up though. That one came to me in a dream one night.




Now I start to realize that my welding head won’t fit in half of those crevices.




Things are starting to come together.




Yay! It’s done and I wrap the ugly welds with header wrap. Good thing, because every pipe is about a quarter inch from something important (radiator, starter, hood, coolant pipes, A/C lines, to name a few).




That little tube is the wastegate dump into the downpipe.




Ball joint braces to support along two axis and allow movement along the third.




I also made a 3” OD, 0.065” wall 304 SS downpipe with V-band inlet. The outlet tapers to a 2.5” flange for my cat (temporary).




Oh, there’s a radiator there! Better weld a flat panel into that elbow in a very critical place for flow. You’ll hardly know that 25 hp is gone.




This guy gets wrapped too. Just in time too, as I had almost healed from wrapping the manifold.




Oh, none of your intake pipes fit now. Better weld up a complete set from scratch. This time it is 2.5” OD, 0.065” wall 304 SS tubing. Did I mention the angry wife?




Downpipe scratched a hole in two perfectly good stock radiators? No matter, just buy a VW Scirocco “racing” radiator to fit where the A/C condenser was.




3 weeks later, we have this. Everything has a heat shield, because everything hot is a quarter inch away from everything that is not supposed to be hot.




So, if you move the radiator to where the condenser was, where does the condenser go? The logical answer is “right where the hood latch and center support used to be”. But the stock condenser won’t fit there. So, you get a custom A/C condenser and lines. And the aftermarket fans go between the F’ing headlights, touching the power steering cooler, which is touching the intercooler, which makes me cut my bumper even more. Good times.


Corbin

'95 ESI-T
Now with more power and fewer leaks



Gimme fuel...Gimme fire...Gimme that which I desire