VW Bus Cold Air Intake

Back when Hapy was getting regular long summer drives, I noticed that the engine bay would get pretty warm. Recall back to the Newberry trip report for example. So, I put together a cold air intake concept to drop the temp going into the turbo inlet. I really do not expect to notice much of a performance difference. While I understand a cold air intake can reduce intake temps, and improve engine performance by a handful of HP, I just don't think what I did will have that kind of impact. Still, it was fun to do.

For someone running the original engine, with the engine tins and surrounding foam in place, this modification makes absolutely no sense. The tins already effectively separate the hot side of the engine from the air intake. If you have lost your tins (or foam), and for some reason cannot replace them -or- you are running a modified engine where tins cannot be fitted, something like this might work for you too to keep the hot side from meaningfully impacting your intake air temperature. This whole bit is triggering memories of that old Burger King advertisement about keeping the hot side hot and the cool side cool.

 

Before I begin, today marks the Ides of March. I am not really sure how to recommend ways to celebrate that. Pay off your debts? Enjoy a celebration picnic with revelry and drinking? Wander out of town in an animal skin? Perhaps we can all just hope Putin will suffer Caesar's fate this day for the inhumanity he is visiting upon our Ukrainian friends. Whatever transpires, in a couple days, it will be St. Patrick's Day. So, I will just get some rest to prepare for that. Hopefully, we can tip a drink within 2 meters of dear friends to celebrate a post-pandemic Spring.

Orientation Thoughts

On topic, consider the VW bay window bus engine bay from the rear hatch (picture on the right is of a '68). Most to the rear on the left is an otherwise unused battery tray. Some folks (like late-bay Westy-drivers) have a luxury battery there to power the fridge when shore-power is not available. On Hapy, there are just a lot of wires, so it's actually not much to look at. The spare tire well hangs down towards the front, meeting the rear tire well. Above to the rear there is a tall open area that eventually reaches the finned ear behind the rear window. Running along the bottom edge, front-to-rear, there is a small lip or perhaps a pinch weld that's about half an inch tall. My thought: wall this in, and create a pass-through for my engine intake, isolating it from the heat generator (engine exhaust and the turbo). Keep the cool side cool.

Parts

My go-to for all things metal fabrication these days (at least for air movement) is HVAC flashing, and this is no exception: I started with some basic 20ga HVAC flashing that I had lying around ($0). Onto the air intake, I need to add a 90* turn ($14US from siliconeintakes.com) so the air filter which used to sit next to the rear end of the spare tire well can instead go into the new cavity. The last piece is pipe flashing (like this) which cost me about $18US to provide safe passage for the aluminum pipe through the HVAC. The air cleaner needs to fit through the hole left in the basic wall when the pipe flashing is removed, so getting one large enough for this purpose was important. I had some HVAC flashing lying around, but at the time I did this, a 4 foot by 3 foot sheet (common size) would have run about $20US. A smaller sheet would cost a little less, but not much. So, all-in this would cost around $50US plus your time.

Cleanup

paper model

I learned along the way that this wall idea is not as straight-forward as it looked. As I started trying to model with a large sheet of brown paper, I realized there were some wiring clean-up items left undone. I tidied up the wiring a little bit, and strung as much as I could into the upper rear corner where the fuel vent line passes into the new cavity, securing them together (and to the vent line) with a cable/zip-tie. Below this bundle of wires, at the rear-most bottom, a couple of wires need to pass as well, so that makes 2 gaps to manage. The front-to-back T-12 cable (See the Chasing the Hapy Electrical Gremlins posts for context) routes into the engine bay where the flat rear meets the upward angle of the rear tire well, so that's a third gap to seal. Last, the stock TDI engine management cable routes into the engine bay from under the center-point of the spare tire well, so that's 4 gaps. Had I planned for this when I did the wiring, I could have potentially cut this list in half, or even reduced it to one. I preferred to not revisit the electrical again this winter, after last winter's adventure. So, I made 4 distinct gaps for wires to pass through. I numbered them in the image of the paper model on the right, here.

Model with Paper

With the wiring bundled, I could start working on the wall... with a model. I started with brown packing paper. These days, so many things ship with large sheets of brown paper as the padding, and that stuff is nice and thick, and sometimes wide enough for things like this. It is also 100% recyclable (unlike the bubble wrap), so I'm doubly a fan. Anyway, I started with a basic measurement: 22 inches deep by 16 inches tall. Of course, I discovered that the hole is not square, and the 22 inch measurement is correct from the bottom of the rear wall to the point where the engine bay curves towards the fuel tank. The top is more than 24 inches from rear to top of fuel-tank compartment. Also, the section is not flat: the bottom curves slightly inwards while the top remains straight.

 

cardboard model 1

Then Cardboard

After a few rounds of test-fit, measure/cut and some added painter tape for strength, or for adding material for sizing, I arrived at an approximate paper model. I transferred the paper model to cardboard with a pencil using some tracing and some angle-square. Consider: the rear wall makes a 90* angle with both the top and the bottom, and (I thought) the rear wall is straight. The top run is straight, though I chose to cut some of the area away which would have been pressed against the spare tire well. I made this choice for 2 reasons: first, the vacuum control valves are mounted there, and I did not want to move them. Second, having a sheet of metal against metal like that would have created rattle noise I would have to solve. With my outline and wire bundle cut-outs defined, I cut the line with a razor blade and cleaned up the edges with scissors.

test-fitting a model

With this stiffer model, I performed another few rounds of test-fit, measure/cut until the cardboard wall completely covered the gap, the wire bundles easily fit through their respective gaps and the edges of the wall were clearly in a place where I could envision mounting. The final cardboard model, in-place in the picture on the right, also eliminated a large triangular shape from the lower front corner which would otherwise have set against the driver-side wheel well. Similar to the cut out from the spare tire well, having a large metal-to-metal contact area would create a vibration-noise opportunity. Looking back, this cardboard wall looked at least as good, if not better than, the final metal wall.

Then Model with Cardboard Again

The front and bottom have a lip I can easily attach to. The top and rear will need some kind thought and some creative drilling. One additional consideration: on the rear pillar, there are grounding points which cannot be disturbed. I decided to add a small tab on either side (above and below) to hold the new wall to the rear. The top will mount directly to the spare tire well for the front 2/3rds. The rearmost section of the top, will not get any treatment at all. I thought about it, and decided that there were already enough planned fastener points to hold the wall stable without adding another hole in the cabin floor. I transferred the cardboard model to another sheet of cardboard after a few repeated fit-attempts. I want to make sure the HVAC, when cut, will fit correctly. Last, I modeled mounting tabs with scrap cardboard and more blue painters tape so I would have them in the right place and the right size when I cut the HVAC. The picture above was taken before I added the mounting tabs to the model.

Plan the Intake Pass-Thru

note imperfect rear line

With the cardboard wall in place, that side of the engine bay looked considerably better... well, it hid what looked bad, anyway. Motivated, I planned the intake route based on the placement of the new 90* aluminum intake pipe. I made a rough cut in that general area of the cardboard wall and put it back in. The 90* pipe is too long on both ends. I needed to remove about 4 inches from the end that juts into the cavity, so there would be room for the air filter (7" tall from rubber grommet to chrome top) without it touching the side of the bus. The filter housing allows for up to 2 inches of pipe before it bottoms out, so there is some wiggle room for my cut on that end. Similarly, the engine-intake end of the 90* pipe needs to be shortened. Again, the silicone collar that attaches the new pipe to the air flow meter on the end of the intake allows for a couple of inches of play. I did not make the actual cuts to the pipe at this point, though.

 

The intake looked about right, so I added in the pipe flashing. I drew the edge of the flashing on the cardboard and then drew another set of lines 3/4-inch to the interior of the tracings. I cut the smaller square out of the cardboard, making a square that was about 6-1/2 inches per side. I tested that I could pass the air filter through that hole. Otherwise, maintenance of the air filter would require removing the entire wall. It fit, but barely, leaving about a quarter of an inch on each side (the widest part of the filter is 6-inch diameter).

Adjustments

HVAC test fit

I transferred the last model above to a sheet of HVAC, but I did not fit properly and had to do another round of cardboard before I was able to get a good HVAC design. The big barrier for me was the location of the vacuum valves (so probably not an issue for anyone else). Ultimately, I removed the valves that were no longer being used (anti-shudder and EGR), and moved the turbo controller to the rear mount. This freed up the front edge of the spare tire well. The second issue will appear for everyone who tries this: I thought that the rear inner wall was perpendicular to the floor and ceiling. It is not. Consider, the contour of the rear of the bus has a slight curve; the inner skin does as well. The picture just above on the right shows the deviation from pure vertical / 90* angle. That picture also shows on the bottom rear corner that the body panels do not have clean 90* transitions either. I cut off that little tab in future efforts. With these considerations, the models were working: showing me how to get to a viable wall.

 

Assemble

prepping the wall

For the second time, I transferred my cardboard model to HVAC flashing, complete with marks for mounting tabs. I cut the HVAC with my tin-snips, and formed the wire pass-thru's with pliers. For clarity, I marked the outline of the hole and then cut crossing lines through the center of that marked area. I folded the triangular bits of HVAC back upon itself to create the opening while also avoiding a sharp edge where the wire bundles would pass. With a hammer and dolly, I smashed the fold-back flat. By doubling the material at the openings, the wall was effectively stiffened; I had not anticipated, but will definitely appreciate that. For the upper rear wire pass-thru, I left a tang or tab nearest the rear wall that I could bend back into place, so the rear edge of gap #1 (visible in the pictures of the installed cardboard model) could get covered up once the wall was in place. Once I drilled the mounting holes in the tabs I set the wall in-place, marked the holes on the bus and drilled them out.

Pipe Flashing

wall installed

At this point, I considered how I would attach the pipe flashing to the HVAC. First, I transferred the square-ish hole from the cardboard model to the HVAC, and cut it. I need to be able to remove this section so I can clean the air filter. I drilled out 4 holes in the pipe flashing, one each per side, where the rubber had dimples for that purpose. I set the pipe flashing in place and marked the HVAC. These spots were within the folded-back HVAC, making the area thick enough to tap. Sweet! So, with a M4 (.75 thread-pitch) tap, I tapped the 4 holes in the HVAC. Into these threaded holes, I sent bolts from the cold-air side with thread-lock so these bolts will act like studs for the pipe flashing. The picture above on the right shows the studs through the HVAC.

Finishing

cold air intake

I moved the wall into place and secured it to the side of the bus with sheet metal screws. I had thought about tapping the holes and using bolts instead. The holes were too hard to access with a tap and I don't think this wall will be coming out with much frequency anyway. Even so, removing some sheet metal screws is not hard. With the wall in, I re-checked my measurements for cutting the aluminum pipe. Once verified with the permanent position of the pass-thru, I cut the pipe down. I pushed the shortened 90* aluminum pipe through the rubber collar and attached the air filter. I sent the air filter into the cavity, and maneuvered the not-filter-end of the 90* pipe through a connecting silicone collar to the rest of the intake. I set the pipe flashing against the HVAC and threaded on the 4 9mm nuts.

 

When I maintain the air filter, the process will be the same as this initial install: remove 4 nuts, loosen the hose clamp and remove the cold air intake assembly. After I clean the air filter, I would re-install by fitting the flashing atop the studs, finger on the nuts, get the pipes connected and then cinch down the nuts.

final install

Now, Hapy has a cold air intake, and the left side of the engine bay is no longer a complete visual downer. Instead, we have a nice clean wall and the engine will get colder air than it used to. This wall does have some small gaps, of course, so the air will not be as cool as it could have been. Perhaps I will circle back later with something on top of the wall to better seal the edges and pass-thru's. Longer term, I may apply a thermal layer onto the engine-bay side to help reduce temperatures even more. The picture on the right, here, shows it in its current (final) state, though a keen eye will see that I had not yet plugged in the AFM (air flow meter) when I took the picture.

 

This took quite a while to actually complete, having started before the 2021 winter holidays. I had other things going on, and this was a lower priority for sure. Also, there were multiple modeling cycles as I figured out the unique puzzles added to the driver side of the engine compartment from adding a TDI (and related vacuum control valves) to the mix.

That's it for today. Thanks, as always, for following along-