TDI install retrospective: Air, Intercooler and Exhaust

Continuing the process of back-documenting what I did to put a TDI engine into an old (1972) air-cooled VW bus. Today I cover the air intake, the inter-cooler and the exhaust. Arguably, these could be addressed independently, but in my mind, it is all one system, with the turbo linking it all together.

Exhaust

I'm starting with the easiest part: the exhaust. When the TDI is installed longitudinally (versus transverse), the exhaust output of the turbo faces towards the front. This doesn't make it harder, it just means that the exhaust that was originally on the car won't work. I brought it with me to the muffler shop, though, so the shop could re-use parts of it. They used the mounting flange, but did their own thing from there. From the flange, it curves down and then rearward, leveling off at the oil pan lip at the bottom of the engine block. Here, the pipe runs straight back and curves 90* towards the driver side where it enters a not-terribly-interesting muffler. The muffler exits into a 90* bend out the rear. Not fancy, nor expensive. I had asked for something bigger, but this has served the need. Perhaps, if I do that Malone tune I've thought about, I'll upgrade the exhaust to a wider pipe.

Air Intake

air filter example

The fresh air intake is very simple as well. I re-used much of the TDI-donor plastic pipes, which route along the driver side of the engine. I attached a small silicone sleeve to the end, where the mass air flow (MAF) sensor housing attached to the plastic, and to that, I connected an extra MAF housing which I retrofitted with a vacuum nipple. This is the source of filtered air for the vacuum system. For the nipple, I simply cut up a small square of metal flashing and bore a hole through it large enough to press a vacuum nipple. I sealed around the nipple with RTV, cut some gasket material to go between the flashing and the housing and threaded it into the spot where the MAF sensor bolts in. Attached to that MAF housing is a large washable B-and-M air filter. I have cleaned the filter at least annually, after each trip into the Central Oregon desert. I have thought of adding more pipe and routing the filter up into one of the high louvered vents. I considered it, but felt that I would need to block off the vent from the engine compartment to really get "cold" air. I'm not sure there is considerable ROI for that effort, but I encourage you to think about it. I still might.

Inter-cooler

The inter-cooler is probably the most complicated part of this effort. Still, it isn't that complicated. First, the inter-cooler on the TDI is an air-to-air, so it needs to be in the air flow to really reduce the temperature of the compressed air. The air flow around a bus is not well designed for passive cooling like this, so I added a motorcycle radiator fan to the rear side of the inter-cooler. This fan is controlled by the same switch as the radiator, pulling air through the inter-cooler. At this point, this fan is the only truly non-VW part I used for this project. Sure, there are aftermarket things, but they are all designed for a VW. This fan isn't, but it was the only thing like it for this conversion... until 2 paragraphs down.

With the reuse of as much of the plastic plumbing as I could, the inter-cooler ended up in a not-so-great location as well. In my case, it hangs from the engine support bar, so the heat radiating from the turbo is kind of heating the air that enters it. I have thought about how to resolve this, but nothing elegant has come to mind yet. Regardless, the length of the run of pipe from the turbo to the inter-cooler inlet is less than 5 inches so there is little opportunity for boost loss. From the inter-cooler outlet, the charged air uses a short run of silicone hose before returning to the original donor plastic pipe up to the intake. I omitted the EGR, so between the intake and the inter-cooler there is the shiny race pipe. This post has some deeper detail.

In order for this layout to work, I needed to replace the inter-cooler from the stock NewBeetle inter-cooler. The stock has the inlet and outlet on opposite sides (one on the top, one on the bottom). This would have forced the inter-cooler to either sit much higher in the engine bay, or have one of the charged pipes hanging way down low. Or, the pipe routing would have required more plumbing. I didn't like any of these options, so I purchased a Saab Blackstone inter-cooler where the inlet and outlet were both on top. This is a fairly common choice for Vanagon conversions which I learned about on the TDIClub forums. Once in-hand, I had to retrofit the inter-cooler with a boost pressure sensor. That meant cutting into it. Not my favorite thing to do to an otherwise functioning thing, but the ECU needs a boost reading. This was simply a case of tracing the lines and carefully cutting them with the Dremel. Once set, I drilled 2 holes for the mounting screws and it's set.

One thing I learned along the way was to make doubly sure that the inter-cooler is being held up entirely by something other than the charged-air hoses. Otherwise, the hoses will eventually work themselves free of the inter-cooler.

appendix:
Prior related posts:
Preparation
Fuel System
Physical Mounting
Vacuum System

Next related posts:
Primary Electrical
Cooling
Secondary Electrical
ECU, dashpod and Sensors