zenith/weber/K&N oil breather solution (long, sorry)

Raymond · 03-10-2002, 03:55 PM

i have a '70T with zenith carbs and wanted to get rid of the stock air cleaner box and replace it with K&N filters and housings sitting atop each carb respectively. the installation of the metal baseplate and filter assembly was simple and looks 10x better then the big stock air cleaner. it sounds great and gives a little more horsepower and torque, so it was a VERY worthwhile upgrade. one problem i encountered was what to do with the oil breather hose that originally routes a light oily smoke from the oil tank to a fitting on the back of the original air cleaner assembly that routed the stream of blowby back into the carbs to be burned through combustion. when you put on K&Ns there's an open-ended hose that emits a noxious blowby that definitely needs to be addressed. at first, i put a little steel wool into the end of the hose so as to keep debris from getting into the hose, and routed it into a factory hole in the firewall and pointed it under the car. well, driving the car almost KO'd me. it smelled like the exhaust pipe was routed directly into the car!!! i didn't see the logic in putting a small K&N-type filter at the end of that hose, it may keep the oily blowby from getting the engine compartment dirty (with frequent cleaning and reinstallation) but does NOT address the noxious fumes! what my dad and i came up with has worked brilliantly and looks cool too! what we did was keep the original, stock oil breather hose and run it into a Earl's Plumbing Y-fitting. the split of the Y runs two smaller diameter hoses into individual Earl's 90-degree aluminum fittings that use crush-sleeves and plug into holes drilled into the tops of the K&N filter housings. it routes the fumes equally into each carb just as the original idea was from the factory. absolutely no fumes, no oily residue in the engine compartment and completely maintenance free. please let me know if there are any questions as to this simple and clean fix. i don't have a digital camera yet or a scanner or i'd post pix.

David McLaughlin · David McLaughlin's Garage

Raymond,
Most photo developers can produce a CD for your pics when you have the film developed. I for one would LOVE to see what you've done as I don't like the set up I have on my car. Sound like a neat idea though.

Raymond · 03-10-2002, 04:25 PM

dave, i will work get some photos of the setup this week. keep an eye on this thread. my dad used to drag race in the early 60's (1955 chevy nomad) so we sat back and thought about how we could fix this. i inquired everywhere i could and nobody had a solution that seemed sufficient, so we "McGuyvered" this and it works. i'll be happy to get the pix on here soon. thanks!

cegerer · cegerer's Garage

Ray, It sounds like a nice setup and I'd like to see it as well. Right now, my breather hose is simply routed out the side of the engine compartment to the rear wheelwell area. It is strapped to the rear of the wheelwell and simply discharges toward the ground. This was installed by Stoddard Porsche when the motor was converted to a 2.5L. I have never noticed any smoking, fumes or anything else from it (maybe I just haven't noticed!)??? There is, of course, an oily residue around the end of the discharge hose, but it doesn't drip. My question now is: should this be routed back to the carbs for performance reasons?? -- Curt

Raymond · 03-10-2002, 04:55 PM

curt, it's routed into the carbs from the factory, all i did was recreate the exact same result through a different method. the vacuum from the carbs pull the fumes and oil through and burn it and goes out where it was designed to... out the tailpipe. definitely pre-emissions! fyi though, before i conceived this idea, i ran the hose out the firewall and pointed it to the ground as well, but it still filled the car with exhaust smell. my car doesn't have excessive blow-by, but it was definitely dangerous and certainly noticable. let's say i wouldn't have taken out a date in the car with it like that. also, i'd recommend putting some coarse steel wool in the end of the hose until you decide what you're gonna do. don't pack it so tightly that it can't expel the fumes, just enough to keep out dirt and such. i'll really try to get pics soon. you know, i was thinking this execution would work equally well with MFI and K&Ns. let me know if you have any further questions!

david w. · 03-10-2002, 05:34 PM

Raymond, sounds like a good set up. I did the same thing this weekend. I bought an adapter from PMO for this conversion. They sell the set up for around 30.00.

The question I have is - what did you do with the one small vac line that plugged into the bottom of the air cleaner? This is the only line I could not figure out where to plug in.
Thanks
david

Raymond · 03-10-2002, 05:41 PM

david, that one i haven't figured out yet. i think it comes from the charcoal canister near the battery and spare tire in the trunk. i put some coarse steel wool in the end and routed it throught the firewall. i didn't detect a vacuum from this line, i think it's just a vent for the gas tank... not sure...

911pcars · 03-11-2002, 01:35 AM

This is the hose reserved for a positive crankcase ventilation valve (PCV) found on most "normal" engines (not Porsche though). This hose contains normal (and abnormal) blowby gases (unburned fuel) from the crankcase and whatever oil fumes the blowby takes with it.

Your hose route back to the individual air cleaners sounds like a good plan. However, I'd suggest installing some sort of catch can between the factory oil filler pipe and the air filter connection. At high engine speed, there can be quite a spray of engine oil from this hose, more so if the rings are a little on the weak side (more blowby). The catch can helps separate the oil from the fumes so only fumes go to the carbs and intake. I used a plastic windshield wiper bottle with some PCV fittings from the local auto parts store to attach the hoses to it. If you track your car, you'll probably need some type of container at the end of this breather hose. I've seen a race car with an 8 oz. Minute Maid orange juice container installed for this sole purpose.

BTW, recirculating the blowby does contribute fewer unburned hydrocarbons into the atmosphere.

Sherwood Lee
http://members.rennlist.org/911pcars
www.seinesystems.com