Aftermarket Exhaust and Fresh Air Hose Fix

[Jadewombat]

Always hated how the fresh air hoses rub against the headers on an aftermarket exhaust. Just plug the fan shroud you say? I drive the bus more in winter than I do summer here. Last winter I bought a TIG welder to be able to do aluminum which opened up a whole world of other fab. stuff I can do now.

Anyhoo, cut two small sections of 2" ID alum. tubing left over from the gas tank project, cut my own plugs to cap the top of the tube, then drilled the plugs for 1 1/2"? aluminum sections of tubing. Yeah, it chokes it down from 2" ID to 1 3/8", but so what. I'll still have airflow and some heat and I couldn't keep it 2" with that small space to work in. Welded it up and simply folded over the fresh air tube on itself (like you would do wrapping a gift). Used a tiny set screw on each adapter to hold it to the mouth of the heater box.

It's tight, but it's not rubbing anymore.

[SCOTTRODS]

Interestingly you talk about choking the flow down from 2" to 1 3/8". I remember many many years ago I bought a Beetle that had restrictor plates on the heater hose that choked them down to probably just about an inch... they were installed in the fitting where it stuck up to the rear sheetmetal. That particular beetle was probably the most complete and original beetle I ever had. I also remember another bug I had having the restrictor plates... the very same ones, in the cooling hose connections where they come out of the shroud on each side. Just a conversational thought. I have nothing to substantiate why or whether these were normal or mods to help in cold climates or cool in warm climates or what... I've seen a lot in my 40 years of VW playing... this just came to the mind when you mentioned your mod, which , by the way, looks perfect for the situation.

[Jadewombat]

Thanks. Yeah, Bernoulli's law of fluid dynamics says the tighter the space the faster the flow, up to a point. I'll report back as soon as it's cold enough to test out the heat.

[SCOTTRODS]

Thanks. Yeah, Bernoulli's law of fluid dynamics says the tighter the space the faster the flow, up to a point. I'll report back as soon as it's cold enough to test out the heat.

That point is the speed of sound (mach), however, there's a bit more to it... LOL The shape of the duct has a pretty big affect too. The abrupt change in cross sectional area will be a restriction, not a convergent duct (which would increase flow velocity). I'm unsure of the dynamics equation for restrictors... I'm sure there's some pressure changes and some velocity changes, but not sure I'd call it a gain. If the pressure increases at that particular point, it will also rise at other exits and flow will depend on the size of EACH exit. So you may see some better flow through your heads, which may present you with a little lower engine temps as well... this may or may not be desirable depending on your weather and requirements for heating and cooling. Consider if you let the air out of an air mattress... through about eight 1/4" inch holes, instead of the intended single 1/4" hole provided...LOL just an example of how the "leakage" could present itself.