Here's my 12V Vr6 short runner build done with limited supplies and tools. I used a 220V mig welder with flux wire. The total cost for the project was about $30.00. Took me about a week working about 3 hrs a night. It's definitely not beautiful but by following some simple build rules outlined by other builders it should flow and perform well. It also has the added benefit of custom throttle placement.
The first thing I did was go to a local scrap yard called "Research Alloys" (in Columbus, Ohio) and picked up my metal. This is the only place in town that allows you to walk around and pick things out to buy as well as selling scrap. I found a 24" piece of 4" Stainless Steel tube, a 24" piece of 3" SS and a 6"x4" 1/4thick piece of mild steel. Cost $15.
Obviously, you'll need an old Vr6 lower intake manifold.
The internal volume of the SRI plenum should be larger then the engine capacity (2.8L). A 20" piece of 4" tube is roughly 4L which is sufficient even after a small section is removed for the lower intake manifold (LIM) flange.
Here's all the supplies needed.(picture taken after project was complete, the metal shown is cut-offs)) The cooking spray is a quick solution to anti-spatter spray. I forgot to mention you'll need a sheet of 1/8" steel for the bottom flange.
Next, I made my templates for the TB and LIM port holes and bolt holes. An easy and accurate way to do this is to tape a piece of brown paper to the object part and gently tap around the hole openings to cut the template holes.
Then, I cut my flange pieces to size. TB: 4"x4" LIM: 2.75"x20". Next, I transferred my template outlines onto those flanges and cut my holes. The six LIM holes were cut using a 1.5" BiMetal hole saw and the TB hole cut using a 2.5" hole saw(had to be widened to 2.75 later). The trick is to use a cordless drill with anti-snap settings. Set the drill so it will click if the hole saw catches hard, that way you don't snap a tooth. Drill the holes at medium speed with medium pressure and frequently add WD40 or drilling oil to the cut. Each hole will take about 5-10 minutes.
Afterward I drilled and tapped the four M6x1.0 holes for the TB and the seven holes for the LIM were drill&stapled at M8x1.25. This allowed the LIM flange to be mounted to the LIM and the port holes made flush and smoothed for better air flow. The threaded holes in the LIM that mount it to the old Upper Manifold were drilled out to about 3/8" to accompany the seven M8 bolts going THROUGH the LIM and threading into the LIM flange. Seven M8 nuts were welded into the flange to receive these bolts. I threaded the flange as well to help prevent leaks.
Next, I smoothed and flushed the seven LIM flange holes using a "carbide burr" (hard to find but you can get a cheaper counterpart at Harbor Freight)I decided not to use "runner compensating velocity stacks" because I didn't have the means to do so and I'd heard the mk4 cams have compensation built in. I guess I'll find out. If you have mk3 cams you may want to consider this extra step.
I used the burr in a drill and went ahead and did a light P&P of the LIM while I was at it just to remove the casting marks and smooth it out.
After the burr, go through with some sanding rolls (grit 80,100,120-also at HF). Then finish with a polishing buff down through the runners.
Here's what the LIM flange looked like finished:
I widened up my TB flange to 2.75" (Mk4 TB) and it was time to cut my plenum tube. I cut it to 20" long and cut a 2.5" section out to weld it the LIM flange. It's difficult to draw straight¶llel lines on pipe. I used the manufacturing lines to make my lines. I mounted the LIM flange to the LIM (to keep it flat during welding) and welded it to my plenum tube.
I grounded off the weld so it wouldn't interfere with the LIM.
After that, I cut my two end caps. One end cap needed a 3" hole cut for my TB flange elbow.
I welded the end caps on and mounted the whole thing to my block to figure out my elbow size. I figured I'd need a turn cut out of my 3" pipe with an outside measurement of 3" and inside of 2". I welded the elbow to the plenum cap and after, the TB flange to the elbow. And that was it!
I used the twisted-braid wire wheel grinder attachment to give the metal a "swirl" finish. I still need to add a small 1/4 plate to the top to mount my vacuum nipples, but I can do that later.
Maybe I will attempt to polish it to a mirror-finish later but I'm lazy so I doubt it.
I reused my stencils to make two gaskets. One to go between the plenum and LIM. The other for the TB.
And that's a wrap. That's all there is to it. I'm sure I missed some things, I will add them as I find them.
Thanks for reading.