72' Type 4 Oil Bath Air Cleaner, Warm air Air Intake Hoses Options

[Ishley]

After 2 years of work....I've completed my '72 restoration...but one thing has me stymied.

I have an oil bath air filter... (pictured) and it has 2 air input points... one is a plastic goose neck and the other is a hose connection controlled by a vacuum system. The mysterious hose I think is supposed to run over to a connection point added to the engine tin...into a "hot air riser". I have no such connection point. I thought my motor was the original 1.7.... which I've now rebuilt into a 2056. I do not have a hot air riser tube.

The only place I've ever spotted a 72 with this type of a air cleaner is on a YouTube video of an original 72. https://youtu.be/w-c6Deg3fBU?si=FPjt3Fhg0lqMsaad Spotted at around 11:20 of this video. The video doesn't show where this hose terminates... but I assume into the mysterious "Hot Air Riser".

I also see in the PET diagrams they show this tube which would bolt to the engine tin behind the cylinder one location. I see a few ebay listings for this tube... but I've never seen it on any of the engines I've looked at.

Does anyone have insight into a hot air riser system.... that bolts to the engine tin behind cylinder one? I don't really think I need it... as this is really a summer only car... but I hate having this unknown empty input point on my air cleaner staring me in the face every time I pop the engine lid.

[Ishley]

I just assumed you were getting the same cars that the Brits got.

[wonkipop]

I just assumed you were getting the same cars that the Brits got.

not quite
we got into emission controls earlier than brits and europeans.
pretty much as per the japanese were the aussies.
we followed you guys with your standards but trailed behind a few years.
our govt (and aus generally) was losing its love of the mother country and going USA after WW2.
in fact emssions standards were one of the things that killed off european car imports into australia in the second half of the 70s. the japanese were on top of all that - we matched their domestic market standards which were kind of in lock step behind america but with a time delay. america led the way. europe really dragged its feet.
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but i think i might have figured out what was going on with the stove pipe for one year.
VW were using it as a stop gap emission control.
quick scan of the parts lists shows they updated the ECU with the EA engines by the looks of it. probably the ECU got a more sophisticated bit of circuitry in there to react to the inputs of intake air sensor. for interim year in 72 looks like the kept older ECU and helped its circuitry out by controlling intake air temp between certain temp limits.

probably if it fell outside those temp limits it suddenly got real dirty on emissions.
each year from 70 the emission limits on certain gases got stricter and stricter on a step by step basis.

they were not using the stove pipe on aussie VWs for emissions i don't think, more for making them idle smooth at the lights and then get a more dense charge at full throttle with cold air. emissions standards lagged too much here (4-5 years) for it to have been a factor on the carby air cooleds in 70-73 in aus.

i reckon VW invented it as an improvement in power and smoothness for the carby cars and then flipped it into action on USA type 4 (or maybe even type 3) EFI as a stop gap interim measure before they updated ECUs to be more sophisticated. that would be my guess.

mr b ( @JeffBowlsby ) who knows his D Jets backwards no doubt has the answer to the reason for the stovepipe to critique my guess.