Fuel Tank Ventilation

[Ferrino]

I have a 1976 fuel tank ventilation system plumbed as follows:

What I would like to do is eliminate hose #5 which runs from a port on the engine shroud to an inlet on the charcoal canister. Assuming all else is equal, this would effectively yield the same setup as found on the SC (and later?), shown here:

My question is: what do the SC/Carrera charcoal canisters have as their "inlet", in lieu of hose #5 in my 74-77 system? Is there a small air filter of some kind?
Thankyou!

[kris159357]

My understanding is that the hose from the fan shroud pushes the air through the cannister.

I recently removed my charcoal cannister completely as one of the previous owners disconnected the system. The fuel expansion tank (2) discharges to atmosphere under the front spoiler. In the PET diagrams there is an option for this. My friend has an 80sc where this was like this from factory.

[Ferrino]

Thanks, I understand the role of the hose - what I'm wondering is how the SC/Carrera system goes without it. From the diagram it looks like the charcoal canister is the same, it just doesn't use the air from the engine fan.

[allaircooled]

Where did you get the second diagram? I don't have an SC to verify, but in my factory shop manual it only shows the top picture and states "All vehicles..." followed by a short description on how the system works with "...fresh air supplied by the engine cooling fan". Maybe the second is a mis print? Just taking a guess here since even the numbering of the second diagram skips #5.

[javadog]

The diagram is correct. It was published in the service training book for the 1978 SC.

I can't answer the original question, since I don't have an example of either charcoal canister to play with and the PET software I have has been updated and no longer contains the part number for the charcoal canisters for the earlier cars. My guess is that they are diffferent, since they are drawn differently on the PET diagrams and there is no third hose shown in the later diagrams in PET.

JR

[allaircooled]

Swing and a miss I guess. Here is a picture I found on the Samba of the part number for an SC (left) and correct for a mid year (center). I got the part numbers from the pdf on the Porsche website.



Now that I am looking at it, that doesn't seem right either so I will go ahead and stop haha.

[ossiblue]

I'll join this discussion only for speculation on the change. I know that earlier 911s had the canister in the trunk by the battery and, possibly, the hose from the shroud was necessary to ensure the fumes cleared all the way to the intake. Later cars (not sure of when the change happened) had the canister in the engine compartment or by the rear wheel and (maybe) it was not necessary for the push of air as vacuum from the intake was adequate.

[joefrantz]

L.J

That makes sense - it looks like the intake vacuum would pull engine compartment air through the inlet side of the canister.

Regarding the last photo: the canister on the left is from a long hood. It is interesting that the 69-73 diagram shows the flow through the canister in the opposite direction from the later ones.

[allaircooled]

Originally Posted by ossiblue

I'll join this discussion only for speculation on the change. I know that earlier 911s had the canister in the trunk by the battery and, possibly, the hose from the shroud was necessary to ensure the fumes cleared all the way to the intake. Later cars (not sure of when the change happened) had the canister in the engine compartment or by the rear wheel and (maybe) it was not necessary for the push of air as vacuum from the intake was adequate.

Looking at the Porsche parts katalog.pdf for 74-77, it shows a hose going from the shroud to the carbon canister. The canister is located passenger side engine compartment. My system is missing so I can't say for sure.

[Ferrino]

My car (76) also has the canister in the rear and the hose from the shroud, so I don't think it's to do with front mounted canisters. I'm guessing they deemed the intake vacuum was sufficient in later cars and dispensed with the shroud pressured supply.

Does anyone have a photo of the canister in an SC? I'd like to see if the inlet to the canister has a filter of some sort.

[antares]

… no just apparently another port for another hose connection … as to where it goes or comes from not certain … you can see the large and small hose connecting the canister in the back and the front single port is disconnected with no hose …. Photos from a 1979 SC 3.0 Targa: