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Just trying to get a little sanity check on catch can installation.
My understanding is that 95 (and maybe 94?) cars do away with the filler neck -> plenum PCV path and only keep the filler neck -> primary turbo inlet path. The latter uses a relatively large rubber hose (~8.5mm I.D.) off the downward-facing nipple on the filler neck which connects to a hardline behind the alternator, then opening up to another (smaller?) rubber hose over the the primary turbo inlet elbow.
My questions are:
Can the filler neck -> plenum path be safely removed and blocked-off on a 93 vehicle?
Is the single 8.5mm hose sufficient for most healthy cars with "normal" power levels (300-400 rwhp)? IRP sells a baffled filler neck with a 1/8 npt port and a -10AN port that they say is intended for use with a catch can. -10AN is pretty big...
That's how i plumbed mine, but i was still getting significant back pressure. Best is probably the 10AN from the fill neck to OCC then vent the pressure to the atmosphere. This may not be legal where emissions is controlled.
I had an aftermarket oil cap that for some reason had a plug glued in the middle. At the track, the back pressure blew out that plug and spewed oil all over my engine bay. It was plumbed just like your drawing
Yes on all your questions. 95 did away with the line from the oil neck to the UIM that has the PCV valve in it.
Street and track cars are TOTALLY different with PCV needs. What will work fine for a street car will fail terribly on a track car.
I've been running a small Jaz vented catch can for ages. I have both the primary turbo nipple and the UIM nipple capped and have the 2 oil fill neck nipples running to the can. IMHO that's a good way to do it. If you have emissions (I would imagine so) putting a sealed in-line catch can is your only option. You can't vent the PCV system for emissions reasons.
The way I did my catch can on both my FC and FD race cars was to bring two 8mm lines to the catch can from the 1) filler neck and 2) vent on the intermediate housing at the base of the filler neck and then simply leave the catch can open vented.
But this will only work on a race car if you have a properly baffled oil pan, otherwise oil will slosh all the way up the filler neck on cornering/transitions on race tires and into the catch can.
Now, if you dont have a baffled oil pan do you want to push all that oil into the primary turbo/intake track?
Nope, so then the answer would be a catch can to engine drain back system like the old Crispy set-up.
Also, you need to mount the catch can as high as possible with the lines running slopped up from the engine so the little bit of slosh into the filler neck can run back down into the engine.
On My FC I had the RB pan baffle and later used it as a template for a weld in baffle into the Mazda Motorsports 7qt oil pan- catch can was on firewall behind the throttle body.
On my FD I have the Winchester/Bacon 7qt oil pan with trap doors and the catch can is where cruise control goes in the non performance models.
On the FD, because the catch can is in a relatively cool spot in the engine bay when I am highway cruising I trap a lot of condensed water and fuel in the catch can. I will get a 1/2 cup or so flamable liquid out from a 200 mile trip.
When racing the whole engine bay gets hot and I just get a ~3tbsp oil per hr on track.
The only time I have had the open vented catch cans fill with OIL quickly is when I blew sideseals in engines and the combustion leak at the rotor flank overly pressurized the sump. But then, I always had baffled oil pans.
But this will only work on a race car if you have a properly baffled oil pan, otherwise oil will slosh all the way up the filler neck on cornering/transitions on race tires and into the catch can.
A baffled oil fill neck is the next best thing to a baffled oil pan
So I went with the same pathing with a catch can that I did on a 400hp EFR 8374 car and where I screwed up was only going with a -6AN sized set up. In this scenario, bigger is absolutely better because blowing out your oil pan seal due to too much sump pressure is not a pretty sight and sucking in engine oil due to your can filling up too fast is not fun at all.
Merry Christmas!
