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PCV system delete pros and cons

41K views 40 replies 10 participants last post by  Mgino96tbird46 
#1 ·
I've already deleted my egr, so the next step would be getting rid of the pcv setup.

The car- my 95 Bird with a PI motor with a bullitt intake and hotter cams.

The plan- weld AN bungs to the top of both valve covers and run hose to a vented breather can mounted on the fire wall or where the battery was.

The reason- because why would I want to allow my engine to ingest oil vapor?

Is there any reason to keep the stock type pcv system?
 
#2 ·
The downside: OCV systems typically emit a fair amount of odor.

The other option would be to keep the system CCV and install a quality oil separator on the PCV to manifold side of the system.
 
#3 ·
When you say odor, is that just a smell?
 
#6 ·
It may smoke at idle also. Many cars do after performing this "mod".

Al
 
#7 ·
What would cause it to smoke at idle and not at higher rpms? I was expecting the opposite.

I currently am running trick flow valve covers with a little breather on each of them. I haven't noticed any issues yet when driving normally. The problem that I have with them is when making high rpm passes, the breathers get too much oil thrown up into them and oil ends up leaking down onto the headers. I figured that plumbing them to a remote canister would allow the oil to get collected and still allow everything to breath well.
 
#8 ·
Yeah, I'm sure it would also smoke at high RPM, but you don't see it and smell it like you do at idle.

Al
 
#9 ·
We also have thin rings; thin rings like to be 'biased' by the vacuum, so they always move to a flat surface; the lack of vacuum can cause rings to flutter at higher RPM's, making them shatter like glass, worst case.

:)


EGR is useful for interstate driving; if you don't do that, you don't need it. You take a big hit in MPG removing it.

PCV is part of the design; I'd want 1.5mm rings at least before thinking of removing it. And I still can't think of a good reason to. :zdunno:
 
#13 ·
We also have thin rings; thin rings like to be 'biased' by the vacuum, so they always move to a flat surface; the lack of vacuum can cause rings to flutter at higher RPM's :zdunno:
While that sounded really good- there isn't vacuum in the crankcase. The pcv valve vents to the atmosphere side of the throttle body... right?
 
#10 ·
You ever ride behind a early-50's flat head motor, smoking under the hood, dripping oil down the road, and stinking?

Yah.

PCV cured all that.

Add the catch can to keep the vapor out of the intake, you get the best of both worlds.

RwP
 
#11 ·
If you're willing to use a canister why not do as Rod suggested and restore PCV with an oil separator inline? There really are no cons to a functioning PCV system besides picking up a minor amount of oil vapor along with the abundance of crankcase pressure and contaminated vapors the system is used for. A separator eliminates that con if it's a big deal. Really deleting it has zero pros, it's a ricer mod like having an open "cai" under the hood, and you're doing more damage to the engine without.
 
#12 ·
And motor cyclists will just LOVE you! <sarcasm> for dripping oil all over the road.

Add the catch can / oil separator, keep the PCV system, and keep everyone happy.

Or delete it. OOOH! Why not put a flat head V8 back in too? Or even better, a Model T 4-banger!!!

*mutters*

RwP
 
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#15 ·
Thanks for the info. I think I will plan on putting the pcv system back in and getting an inline oil separator.
 
#19 ·
Speaking of oil separators. What do you guys suggest on a boosted setup (vortech)? I am not deleting PCV and putting breathers, I'd rather have no excessive pressure in the crankcase cause boost will increase my blow-by. But since I'll be rerouting the PCV to the front of the supercharger where I guess I'd have a lot more 'suction' and I don't wanna end up sucking oil from the valve cover into my intake lol, just the vapors. So I'll need some sort of separator.
 
#17 ·
The little air compressor separators do not work as well as a quality unit from UPR, JLT, etc. Been there, tried it, tried it again, then ponied up the bucks for a better part.
 
#18 ·
Here is a link to a sealed catch can. The price appears to have crept up since I got mine years ago, but they work.
Saikou Michi Co. Home

This is on my Toyota - I have a can with 3/8" fittings inline with the PCV hose, and one with 1/2" fittings for the breather side, returning to the intake pipe. In both cases, I have the catch can mounted low in the engine compartment.

Once a year, I drain an ounce or two of oil from the PCV side. I don't have any oil on the breather side, but I am sure on my high mileage engine I would have had a significant amount.

Al
 
#21 ·
When I had had the turbo on my 95 I left the PCV alone as is. The PCV is already a check valve. I had a remotely mounted breather filter ran from the driver side valve cover incase it threw up oil under boost but I never had an issue. Under normal driving idling (no intake pressure) the PCV would operate normally. Under boost pressure the PCV would prevent pressure from bleeding into the crank case and allow the case to vent out the breather. Considering on a street car your only in boost for a few seconds it's not usually a big deal. I think a lot of boosted cars have used this basic design. Diesels for example use a CCV as that the crank case is closed and you have a vent from one valve cover typically routed pre turbo. My powerstroke stock had a 90° feed from the CCV to intake tube and pointed towards the filter as to reduce any kind of high velocity venturi effect. I now run a blower on my powerstroke and feed the CCV to a low venturi area at the blower inlet along with one of those T strainers I posted above. Has greatly reduced oil being sucked into the induction system which is great because if the engine is running its seeing pressure in the plenums.
 
#24 ·
On a Supercharged car that is fine and likely best to do as you will be pulling thru the MAF but I was blowing thru the MAF and did not have the option. I never got into the tuning of that setup for it to be correct but no reason it can't be compensated in the calibration it's a small vacuum line. Whether correct or not is an opinion and I'm more concerned with will it work.
 
#27 ·
With a blow-through centri or turbo setup, the apparently opinionated correct method is to run a OCV system.

It can only be compensated for so much in the tune, you may be able to fudge a few tables to account for some of the unmetered air but you may as well run a carburator if you're just shooting for "good enough, it works". If you're going to delete any part of PCV, delete ALL of it.
Bingo.

After deleting my egr on several cars i didnt knowtice any drop in mpg...
My current car i gained, buut i did add an npi manifold,75mm tbody plenum and intake..
It went from 150ish to 160s. Same drive ,same grade gas and filled up until the gas pump clocked off each time to try and make it as accurate as i could.. And at 160 the needle was still abit above half a tank.
That method isn't accurate, as you're relying on the accuracy of an inaccurate gauge. Divide gallons by miles driven.
 
#29 ·
It would only be an unmetered leak out of boost. Also the Pcm I believe does not use MAF input under WOT conditions anyways? Either way I never had an issue running a PCV that way even untuned. I ran a breather when the engine was mostly stock as well and never had any problem. When I was running the PI motor with the small turbo I did however modify the MAF and installed larger injectors to incorrectly richen AF as I never got into tuning in those days. I still don't understamd why it could not be compensated for unless the software you are using has limits on adjustments to the file. Some tuning software has no interlocks and you have full control.
 
#26 ·
After deleting my egr on several cars i didnt knowtice any drop in mpg...
My current car i gained, buut i did add an npi manifold,75mm tbody plenum and intake..
It went from 150ish to 160s. Same drive ,same grade gas and filled up until the gas pump clocked off each time to try and make it as accurate as i could.. And at 160 the needle was still abit above half a tank.
 
#30 ·
You can run the car without a MAF at all if you wanted to, running purely off of the tables, with no feedback, it'll work just like a carburetor. Yes it can be compensated for in tuning software to an extent, but asking any repudiate tuner to dial in your car with a vacuum leak and you'll get the same look of bewilderment from them as you would asking a shop to align your car without fixing the tire leak. You don't fix a problem by trying to make the problem work.
 
#32 · (Edited)
Even if the PCV valve did not seal it would be a very small boost leak. You can also add another check valve in the PCV to intake line. I had a question mark after the MAF question as I was unsure. I have yet to tune anything that uses a MAF. I had only read on some older information back in the day that the MAF was ignored as things were happening faster than a MAF could feedback input to the pcm. Again it may not be right but will work and did for me even untuned. I'm also not talking about asking a reputable tuner to dial in your engine with a unmettered leak. Many tune thier own combinations. Also I as a customer if getting custom tuning done and paying good money were to ask a tuner to compensate for this or that and they were to look at me strange I would pack up and find another tuner. I have personally known reputable nationally known tuners who will do what it takes to make a combination work even of they would not do it that way.

Again just my opinion and experience. I have used software to compensate for all sorts of changes on PCMs PLCs, CNC, and other automation controls.
 
#33 ·
Anyone with the capability and knowledge to tune their own combinations should be aware of the flaw and futility of this endeavor, an unmetered vacuum leak is a completely unnecessary and defeating variable to tune around when your primary objective is to simply make the car run right using the measured scientific data given, not assumptions and anecdotes. I know tuners who will tell you straight up that your car will be a pain in the ass to tune unless you change this, this, or that, wise ones indeed will turn you away just to avoid the potential hassle of an unsatisfied belligerent customer whose combination was, as suspected, an unnecessary pain to tune.
 
#35 ·
It's really hard to model a vacuum leak: With a fixed leak area, the leak volume is proportional to the pressure across it, the humidity, and the barometric pressure; and it's nonlinear.

You don't know what the vacuum level is, so you have to guess, and the barometric pressure/humidity relationship is based on that guess, and you have to model a fueling response based on those guesses; so that makes your mix at any given time a third-order guess relationship, and that will never ******* work. :)

Enough time and effort could model the response for a given leak for a drag run, changing absolutely nothing on the car, but it would take months to tweak. And fail if the weather wasn't close to the same.

And if the leak area changes any, every assumption you made is now wrong.

:)
 
#36 · (Edited)
Not to say it's the correct way. However it could work as many have done it including me. If my setup ran fine untuned it would likely be even better had it been tuned. In a draw thru application it is not an issue as you can have the line plumbed after the MAF. However on a blow thru you cannot. Unless you run a bunch of check valves and a check valved external vent along side the standard system to alow the crankcase to vent pressure when boost pressure has forced the PCV and breather line check valves closed. As the way I had it under boost when fueling is most critical there is no unmetered air as the crankcase is vented to atmosphere.

Most are not running a blow thru MAF here anyways unless they are running a Centrifugal.
 
#37 ·
I'm just saying that by not having it predictable, you're obviously running rich enough that all your parts are remaining in the engine, over variations in weather.

That leaves an enormous amount of power on the table; you could pick up 25% in the really bad spots.

That's the only reason I mention it; I bet any of our racers might trade a relative for 25%... :)
 
#39 ·
Keeping the CCV is the way to go. I'll do the separators. I don't wanna do it the cheap way, cause there are benefits of CCV that I feel are necessary to the life of the seals and what not.

Also people saying the MAF is ignored at WOT, that's so untrue, it's probably the most critical at mid-high throttle stage. MAF is a super critical EFI component, really can't do a self-tuning EFI without some sensor that detects air intake.
 
#40 ·
Sure you can. Speed density, utilizing a MAP sensor, is a pretty common self-tuning EFI platform. That said, for the setups we're talking about here, there is no cause to jump over to that school of thought/tuning.
 
#41 ·
There's a reason why Ford ditched speed density, it isn't as precise as MAF fuel injection. Because there's a MAF sensor, the computer can adjust itself around wear and tear and modifications, to an extent. CCV is the way to go...and stay.

FWIW, JLT makes awesome PCV air/oil separators. My high mileage 11.2:1 setup was filling a 1 oz catch can every fuel tank.

Strangely, or not, my 250,000+ mile 5.0 mustang doesn't fill it nearly as fast.
 
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