Carrera airbox vacuum line to carbon canister - needed? block off?

r-mm · 01-02-2015, 09:30 AM

Happy new year all

Getting to some deferred maintenance including replacing my cracked airbox. I did not previously have the vacuum port on the back of the airbox hooked up to anything - PO had some strange stepped down connection plastiwelded on there. Now that I have a clean uncracked airbox - I'm wondering if I can't just stop this connection up with a vacuum cap? Presuming its function is to draw vacuum thru the carbon canister and clean up fuel tank fumes, and that it has no effect on performance, idle, etc?

Wondering if PET from my model year ('87) doesn't even indicate it as stopped up from the factory?

The vacuum diagram is from another post, I think for an '86.

Thanks

gliding_serpent · gliding_serpent's Garage

you can block it off no issue. The benefit to my understanding is to draw air from the fuel canister on start and burn any fuel vapor it might contain that has made it's way from the gas tank and through the charcoal canister. The PO blocked it off on my car, so I just did a canister delete. My car may smell a bit more like fuel in the heat, but then so will my 2002Tii, and they are stored together... so who cares.

Arne2 · Arne2's Garage

I just hooked mine back up after having the airbox off for oil leak repairs yesterday. While I can't see any performance or running issues to plugging the airbox port, I don't see any advantage to doing so either. The only possible downside I can think of would be if you get gas fumes from the canister.

steely · 01-02-2015, 02:23 PM

That's interesting that the PET shows a stopper.
My only input to your question is that I don't know that it'd make a big difference performance wise either. And just as an observation, I have an '87 as well, and the line between the canister and the air box is indeed connected.

r-mm · 01-02-2015, 02:42 PM

Steely can you tell me what that line looks like? I'm not seeking performance, just want not to rock the boat, but since the line was disconnected when I got the car (from a guy who kept it well) I don't know if there was something downstream that was problematic etc. If I can't find the line easily I'll cap it so no dirty air gets sucked in.

ganun · ganun's Garage

Let us know where to source that particular cloth braided hose, I've tried many web sites and nothing, .....IIRC 10mm I'd, I don't recall.
I have a plug on the air filter box and the end of the hose, which is too short just lays there.
Haven't smelled any gas smells at all.

steely · 03:11 PM

Mine is original - I guess I should replace it.
Sorry I don't know where to get it from, I never looked here on PP frankly because I never thought of it until now.
I think it is bigger than 10mm.

gliding_serpent · gliding_serpent's Garage

I came to learn about this system when I found this plugged line while removing my AC. At first I was worried I pulled something out, until I saw that a PO plugged it.

Here is my thread on the issue when I came across it. Post #5 gives some helpful links too. What is this hose/wire for?

steely · 03:25 PM

pic # 1

pic #2

pic 3

pic 4

pic 5

r-mm · 01-02-2015, 03:14 PM

Thanks. Just to be clear, the part in the near side of the photo is the side that "should" be connected to the nipple on the back of the airbox?

Drymartiniwi · Drymartiniwi's Garage

I also have a 87 coupe and I replaced my air box with a K&N cone shaped filter for better breathing and I just plugged it up. Really doesn't make a difference in performance. But plug it to avoid any fumes.

gliding_serpent · gliding_serpent's Garage

yes, if we are talking about my photo.

Edit: no. My line featured would connect to the gas tank. see post below. My mind is faulty.

steely · 01-02-2015, 03:20 PM

Quote:

Originally Posted by r-mm

Thanks. Just to be clear, the part in the near side of the photo is the side that "should" be connected to the nipple on the back of the airbox?

If you are referring to my first picture (i should have numbered them) - the filter element is exposed on the left - face on. The hose is connected to the 'rear' of the air box. The camera is pointing across the engine toward the drivers side. It was a blind shot.

Does that answer your question?

r-mm · 01-02-2015, 03:21 PM

Yup - I didn't think this would be such an active topic! Thanks all, I'll take another look at mine tomorrow.

By the way, do we know what causes our airboxes to crack?? Is it that they are fastened in part to the intake and in part to the AFM and also have those oil hoses piggybacking on them? Or is it the high torque clamps used to close the airbox? Eager not to crack my replacement as they aren't cheap and seem to be getting harder to find.

Incidentally, I got a kick out of the fact that the airbox in the Bentley manual was drilled full of speed holes ha!

steely · 01-02-2015, 03:21 PM

The line is gliding serpents' pic is the 10 mm line that is supposed to go to the fuel tank - IMO.

steely · 03:28 PM

Quote:

Originally Posted by r-mm

Incidentally, I got a kick out of the fact that the airbox in the Bentley manual was drilled full of speed holes ha!

I don't know why they break.
The PO of my car cut out the cover leaving the retaining edge with clips - one big speed hole!
I found another here used with the snorkel and bought it just in case.

Incidentally, in my first pic I see where I am missing a screw!?

on edit
In (recently numbered) pic # 2, the vacuum line bracket is supposed to be screwed to the rear of my air box.

gliding_serpent · gliding_serpent's Garage

Quote:

Originally Posted by steely

The line is gliding serpents' pic is the 10 mm line that is supposed to go to the fuel tank - IMO.

You beat me to my own edit! I was just reading my old post on the issue. thanks.

steely · 01-02-2015, 03:28 PM

Quote:

Originally Posted by gliding_serpent

You beat me to my own edit! I was just reading my old post on the issue. thanks.

sorry - am usually a half-fast typer.

gliding_serpent · gliding_serpent's Garage

Quote:

Originally Posted by steely

I don't know why they break.
The PO of my car cut out the cover leaving the retaining edge with clips - one big speed hole!
I found another here used with the snorkel and bought it just in case.

Incidentally, in my first pic I see where I am missing a screw!?

on edit
In (recently numbered) pic # 2, the vacuum line bracket is supposed to be screwed to the rear of my air box.

My po drilled my airbox. Given the snorkel opening is also dented, I will just be cutting my airbo cover open as you describe. Some call this "cup style" as it resembles the airbox style found in the cup cars. Good for 5-6hp on a stock 3.2 according to Steve Wong data. More if your engine is higher output. Needs a chip tuned for is presence however, otherwise it just throws off you afr ratios, and thus power.

here is the data: 3.2 Dyno Tests: Airboxes and Mufflers

r-mm · 01-02-2015, 03:34 PM

Since the business of this thread is complete I'll jack it myself. Should I Wong Chip my car? Stock, rebuilt top end, cat bypass and bursch quiet street. Really don't need or want more power (like being able to redline it in a few gears without license danger) but the promise of drivability, responsiveness and maybe even economy sound like nice things.