In troubleshooting my wife's oil consumption issue, I finally stared learning the PCV system (already knew what it does... but not how). That got me thinking about my car & whether or not there's a better way to set it up. 'Twas fun learning that C5s used three different PCV configurations over the years... yet so many interweb wizards claim their explanations are for 97-04 models. That's when I started taking everything I found with a grain of salt.

Identifying the baseline, here's how I understand my 2000 (no valley plate oil separator) originally routed... with the caveat that folks using a 90mm LS7 throttle body have to pull fresh air from the intake tube between the TB & MAF:


With that in mind, here's how you'd add a catch can to that setup:


Now here's where I could use some expert analysis:

1. I've got a PD blower on my car. The PCV vacuum & fresh air ports are both pre-compressor, so it won't pressurize those lines like a turbo or centrifugal does - meaning you can route a catch can the same as a N/A engine. Its PCV vacuum barb is on the opposite side, though, and my LS7 throttle body moved the fresh air barb to the air bridge.
2. Mine is using a speed-density tune, so running breathers won't throw lean codes because it cares less about unmetered air (MAF is unplugged).
3. My current configuration is illustrated below. Rather than the intake's constant vacuum barb pulling PCV air out the two firewall-end valve cover ports (back-filled by fresh air coming from the air bridge into the passenger valve cover's front port), what I see is that both valve cover dirty ports (firewall end) and the fresh air inlet port (passenger front) all go into the catch can - drawn by weaker vacuum into the air bridge. The filtered oil cap with no check valve allows fresh air in to replace it but also allows crankcase pressure to vent to atmosphere (bypassing the catch can / intake tube).

While I appreciate that none of the oily vapor seems to be going back into my engine (dry air bridge), I think there's likely a better way to circulate air through the crankcase. Also, the can ain't caught much of nothing in the 10k miles it's been routed this way - even after a lot of hard driving... my guess is that it's all going out the filtered oil cap (which is visible at idle when the hood's up) because that's the path of least resistance. It also appears to mostly vent itself out the oil cap via blow-by pressure because the air bridge doesn't see significant vacuum unless you're on the gas (blade open), equating to a lack of strong & consistent draw on the PCV lines... and even then - considering path of least resistance - would having the catch can connected to the barb right beside the oil cap draw mostly outside air instead of PCV?

Change ideas so far:

• I shouldn't simply swap back to a normal oil cap because that'll keep the crankcase under vacuum without a fresh air source. I could, however, force vapor through the can by installing a check valve that only allows air in through the oil cap.
• I should draw PCV vacuum from the driver's side barb behind the throttle body instead of the air bridge because that'll maintain a constant & stronger draw through the PCV system instead of only when the throttle's open.
• I should either cap the passenger-front barb so that fresh air doesn't immediately exit through it... or apply Change B + return to a standard oil cap, pulling fresh air from the air bridge (back to a closed system).
• Say "F--- it all" and go with a couple road draft tubes.

Thoughts & suggestions from the crowd?


And here's a blank picture if you'd rather draw out your own examples.

 

any thoughts?

 

I would essentially follow what Mighty Mouse suggests for an LSA style setup, just with a small change due to not having vacuum drawn from the valley. Instead, continue to pull vacuum from the passenger's side valve cover through the catch can to the constant vacuum port behind the throttle body. Then plumb the driver's side valve cover to pull fresh air from the air bridge. A check valve their would be beneficial. That should keep a fairly clean setup, but also allow fresh air to "sweep" across the motor and force any flow under boost to go through the catch can as the blower pulls it. That may not actually be the case of how things work at all, but it aligns with Mighty Mouse's diagrams and makes sense in my head.

 

I didn't have time to read the entire thing but you also know that you're welcome to call me anytime. Setting it up in the air bridge doesn't prevent oil from entering your intake tract, it only lowers the amount of vacuum that you get for your PCV system in your case. Use the capped port and abandon the one in the air bridge. This way you'll get the best vacuum source at all times. If this doesn't completely address all concerns/questons, then give me a call and we can discuss it more completely. Not sure that it matters but for those that aren't aware of my relationship with the OP and his car, I tuned the car and performed some other work on it.

Bret

 

thanks for the chat this morning, Bret. i understand pulling vacuum from behind the throttle body instead of from in front if it will increase the PCV draw (along with the amount of potential vapor into my blower)... i just wasn't sure if having the traditional fresh air inlet port connected to the dirty side (right beside the new fresh inlet) was actually pulling much from the two firewall-side dirty outlets.

the more i think on it, it seems like maybe i should simply remove the T going into the can and cap the stock fresh inlet port (only pulling dirty PCV from the rear of each valve cover). since that line Ys mid-way between the two, it should theoretically draw fresh air more evenly between the two sides from the oil cap... understanding the driver's side would technically have farther to travel / more volume to fill & therefore flow slightly less. but that should at least force fresh air to the backs of the heads instead of allowing it immediately back out the vacuum line into the can.

that should result in increased circulation. and by leaving the filtered oil cap, it's still the easiest exit under crankcase pressure & should keep much of the dirty vapor out of the intake tract (whatever vapor does head that direction goes through the can).

the MM can design is quite effective in both filtering and alleviating reverse pressurization. i've also studied that diagram, but where i have a tough time equating it to my setup is that it looks to be based on the latest GenIII PCV setup (two versions beyond mine) and pseudo-reverses the flow direction based on a simple driver's side orifice (instead of a one-way exit valve), and it's missing the passenger's side dirty port in favor of a valley oil-air separator that my engine ain't got the clearance to utilize (the blower kit actually changes LS6 covers to the LS1 cover). thanks, though.

 

and i wasn't trying to call Bret out for thinking his setup was bad - just looking to see if there's a more-efficient way.

i'm taking the blower off in a few weeks to install a plenum spacer (improving intercooler efficiency & reducing airflow restriction into the heads), so i simply want to ensure i'm putting it back together in a good way.

 

would you be able to swap to an ls6 style valley cover with the plenum spacer?

 

no sir.
you might be thinking of the LSA spacer plates that raise the blower up off the heads.



this spacer sandwiches between the two halves of the TVS's manifold (leaving the blower-to-head/valley spatial relationship the same).

 

and after i finished installing a closed system catch can on my wife's truck this weekend, i used some leftover 3/8" fuel line to simply eliminate the T going into my car's catch can.

it's now just the two rear dirty valve cover ports going in. the original fresh air port is capped (well... temporarily plugged because i apparently need bigger than a 3/8" cap to fit over the ridge on the nipple), and fresh air is still drawn in via the oil cap. positive case pressure with low PCV vacuum still vents out the oil cap.

i think this should meet in the middle between "ingesting vapors that make it past the can" and "barely circulating air through one corner of one valve cover"