73 super air cleaner assembly

[Brock36]

How important is the exhaust air into the cleaner and carburetor?

[Ol'fogasaurus]

Maybe I am misunderstanding the question, but exhaust should not be going back into the carb/air cleaner or engine. It would cause problems you don't want.

Lee

[R2.0]

Was 73 the first year for an EGR system?

[Bruce2]

I know US 49 state required an EGR in 74, but don't know about other years for Calif. Maybe it started in 73 there.

[Bruce2]

Maybe I am misunderstanding the question, but exhaust should not be going back into the carb/air cleaner or engine. It would cause problems you don't want.

Lee

You should know about EGRs, you were around in the 70s!
Exhaust Gas Recirculation.
At part throttle conditions, a small amount of exhaust gas was put back into the intake manifold. Since all the chemical components of exhaust are already burnt, what's put back is inert. This inert gas is significantly cooled by the time it gets back into the chamber, so when the spark happens, the inert gas absorbs some of the heat created. This lowers the combustion temps significantly, which reduces the NOx emissions.

Now you might be thinking that would reduce hp. You would be correct, but you can just give it a bit more throttle to make the hp you want. It won't make you consume more fuel since it displaces some of the A/F mixture. It also won't affect the maximum hp your engine makes because they all have a bypass at WOT.

[Ol'fogasaurus]

Maybe I am misunderstanding the question, but exhaust should not be going back into the carb/air cleaner or engine. It would cause problems you don't want.

Lee

You should know about EGRs, you were around in the 70s!
Exhaust Gas Recirculation.
At part throttle conditions, a small amount of exhaust gas was put back into the intake manifold. Since all the chemical components of exhaust are already burnt, what's put back is inert. This inert gas is significantly cooled by the time it gets back into the chamber, so when the spark happens, the inert gas absorbs some of the heat created. This lowers the combustion temps significantly, which reduces the NOx emissions.

Now you might be thinking that would reduce hp. You would be correct, but you can just give it a bit more throttle to make the hp you want. It won't make you consume more fuel since it displaces some of the A/F mixture. It also won't affect the maximum hp your engine makes because they all have a bypass at WOT.

I did look "EGR" up and I kind of remember now hearing EGRs being talked about but that was a long time ago too.

https://en.wikipedia.org/wiki/Exhaust_gas_recirculation

At that time, we were busier taking stuff off and adding aftermarket manifolds, carbs, ignition and headers not so much concerned about that "tech stuff". "That tech stuff" came into play later.

Lee

[Brock36]

Some think that the warmed exhaust helps with warm-up in winter here in Canada. I don’t know if EGR is required here.

[P_Vilefort]

Type 1 cars didn't get EGR in California until the 1977 model year on fuel injected engines. This was a California only thing. It was not used on any other Type 1 cars with or without fuel injection. What you are referring to is the air preheat hose from near #1 cylinder to the intake nozzle on the air cleaner. It has nothing to do with exhaust gases. Air preheat reduced the tendency for icing to form in carb throat before the intake manifold got hot.
Get out the Bentley Manuel for the 1970-1979 Super Beetle, Beetle and Karmann Ghia models and look in it. This is a perfect example of how things can get off track when you don't communicate properly or when the original post was not very descriptive
.In 1972 when other American production cars were already using Positive Crankcase Ventilation VW was still using a road draft tube; venting engine fumes to the atmosphere. For the VW engine EGR was only a California requirement in 1977. After 1979 it doesn't make any difference. The Mexican models had EGR along with fuel injection. The only time EGR was operational was at idle and continuous low speeds; high manifold vacuum needed.

[P_Vilefort]

It is not exhaust. It is air preheat. The hose that you have on the right side is in the wrong location. It should be in the hole behind the hose. That is the location of the heater box. Where it is now is the location for the air preheat hose to the air cleaner inlet snout.
Get a Bentley manual for cars 1970 to 1979. Look up online "VW 1970-1979 Bentley Manual Super Beetle, Beetle and Karmann Ghia. It is an orange cover and you may find it as an online PDF. There is also the owner's manual you can find at TheSamba. . https://www.thesamba.com/vw/archives/manuals/72bug.php

[P_Vilefort]

EGR was a California only thing and didn't occur in VWs until 1977 and only on fuel injected engines. No other states require EGR on the air cooled VWs.

[P_Vilefort]

Brock36
Intake air warming prevented carburetor icing and it was used on ALL American built automobiles. This only disappeared with the introduction of fuel injection. It was also found on all European and Japanese vehicles with carburetors. It doesn't need to be freezing for carburetor icing to occur.

[sideshow]

I agree in that the air cleaner expects "warm air" source and not exhaust gas.