PCV questions

[ralph]

@KillerB (and anyone else with opinions), I put a PCV on and my idle is way higher now.  Theories?...

 

No ill effects to power or rev-ability so far (if anything, it requires less clutch finesse off the line now).  Will throw the stupidly-overpriced ECU cable on it and see what the numbers are, maybe back the idle screw down a bit since I raised it above the target TPS voltage before. 

 

Related:  is it possible that US cars get an ECU with mapping appropriate to having a PCV present?

[MV8]

Can you post a pic of your pcv installation?

[ralph]

The PCV itself is one of these (cheapest I could find):  https://www.summitracing.com/parts/URO-016453

 

 

...and working left to right in the admittedly subpar photo here, you've got the stock catch-tank cap and hose, with the hose pulled through so an inch or two is still in the bottle (definitely keep the end away from the bottom so the vacuum doesn't draw spillover oil into the plenum), the other end hose-clamped onto the inlet of the PCV (which has directional markings) just under the plenum on the left, and since the outlet barb is small, there's a section of smaller hose to allow the stock caterham hose (spare bit unused in build) to be cinched down over both, while the other end fits snugly to the hole in the plenum that comes with a blanking hose cap of sorts clamped onto it.

 

As with most of my build, this is solid B- quality work.  Modesty prevents me from showing pics of the other side where I wrapped the headers in fiberglass jackets with all the finesse and aesthetic sensibility of a 2yr old putting their toys to bed in a blankie.  In my defense, both these mods are function-before-form, so, style points are inapplicable, IMO...

 

The fiberglass header wrap lets off a bit of smoke at first (I assume they use some kind of light oil during manufacture to get it through whatever sort of loom weaves the stuff), so I had some words with the CHP this morning about why I was driving a car with no license plate that had smoke drifting out from the bonnet gills.  After inspecting the paperwork, the officer asked to see the VIN on the chassis, and I will admit to being more than a little apprehensive about pulling the bonnet off, but all was good.  He agreed that the car was better off at Laguna, and thanked me for following the process by the numbers.

 

BAR ref (virtual) appt on 8/23...

 

 

 

[MV8]

At idle, the pcv should be "closed" (minimum flow orifice which varies depending on the pcv) by manifold vacuum being greater than crankcase pressure and the pcv internal spring combined. The spring is balanced against manifold vacuum, to fully open part-throttle through WOT when crankcase pressures are greatest.

Minimum flow should raise the idle speed by 50-100 rpm in a system that has a breather port as far from the pcv crankcase port as practical. This port allows air into the crankcase and is usually plumbed into the air cleaner base but a small motorcycle open breather does the same thing. There is essentially no emission from an open crankcase breather when running when there is a pcv valve in the system. A "closed" system just pulls through the engine air filter and no different from an emission standpoint. However, a breather right next to the pcv port on the tank or a valve cover would essentially disable or reduce the pcv function, but the idle speed increase is normal if not excessive and should be readjusted at the throttle idle stop.

If you experience oil gasket leaks/seepage or oil in the intake, the crankcase pressure may be excessive or too low under some conditions since it is sealed with no breather. I would connect the pcv to a port on the valve cover or where it normally is on the engine donor vehicle and leave the catch tank clear hose open to allow air in or add a small push-in motorcycle breather for that size hose so no trash is pulled into the system or zip tie a piece of residential window screen over the end of the hose.

The overall flow of the pcv system can be reduced for less effect with an inline orifice but a bad idea without a breather for the crankcase.

 

EDIT: so I see this is a duratec, which should have a plastic breather box under the intake with a pcv valve in the top of it. It could have an aftermarket plate installed with no openings. I see a cluster of hoses below the intake in your pic. Maybe you already have a pcv?

Edited August 19, 2023 by MV8

[KillerB]

This (MBZ PCV) is what I installed between intake manifold and catch can. Zero impacts to engine idle or anything else. Removed post ref appt, since it’s not really needed, let alone useful in our (dry sump) application. 

[MV8]

It looks like Ralph has it inverted compared to Killerb. No idea how it is oriented on a merc. With it idling, rotate the pcv so the arrow points up and see if it has any effect on idle rpm.

 

Take a pic of the side of the block below the intake manifold.

[ralph]

Mine's pointed the same direction (arrows point to plenum, which is the desired flow direction).  Pinching the hose on the catch tank side of the PCV restored normal idle pointing to a vacuum leak upstream (catch tank cap has a hole in it -- plugged the hole, so now the system is more "closed" than previously, but I haven't tested it yet). 

 

@MV8 re:pressure/vacuum I thought positive crankcase pressure and negative intake pressure (vacuum) would both push/pull against the PCV spring to open the valve...so, I'm confused there as to why intake vacuum would need to exceed crankcase pressure -- they're both opening the valve, no?  Also, if there is a breather/inlet on my crankcase, I'm not finding it...looks like it's just one line from the rearward part of the crankcase to the sump tank.

 

 

[KnifeySpoony]

AFAIK the 420R (with it's dry sump) is not possible to have a "proper" PCV setup. I think you just need to have something in place that will pass inspection when you go to the BAR. Some of us had nothing and still passed...

[ralph]

That makes sense.  As far as "proper" PCV setup, while what I have doesn't quite pattern-match the typical setups, I can say that it's a closed system where crankcase blow-by does enter the engine (albeit on the wrong side of the air filter).  As many have suggested, the whim/mood of the BAR ref at the time of inspection may play a larger role in this than the technical particulars...we'll see.  I sent them pics of what I've got, so if it's totally out of line with their expectations, I figure I'll hear about it before the actual on-site...

[MV8]

I misspoke. It is confusing. Idle= manifold most negative pressure (strongest pull against spring same side of valve), Crankcase lowest positive pressure (weakest push against spring opposite side of valve). WOT= least negative pressure, CC highest positive pressure for a net pressure increase to open the valve but this is just one kind of pcv. A valve control matched to the dynamics of blow-by over the life of the engine would be ideal.

I know it is pointing the same direction but the orientation is not the same. With it idling, rotate the pcv so the arrow points up and see if it has any effect on idle rpm. Do not change the hose connections to do this but if the hose from the catch can is too short, disconnect it from the pcv to perform this test. In other words, grab the pcv and rotate it 90 degrees ccw at least, leaving the engine side connected and idling. If this drops the rpm increase, you could add an elbow fitting below it and shorten the hose above so the pcv hangs straight down, then runs straight forward to the catch can. A solid insert drilled for some flow (1/8"-1/4" bit?) and placed in the hose near the pcv would reduce the rpm increase and still be functional using a valve not intended for that engine.

There are oem dry sumps with pcv valves but most dry sumps are added for racing where it isn't required or desired.   

[KillerB]

On 8/23/2023 at 12:58 PM, KnifeySpoony said:

AFAIK the 420R (with it's dry sump) is not possible to have a "proper" PCV setup. I think you just need to have something in place that will pass inspection when you go to the BAR. Some of us had nothing and still passed...

Very true. Considering that physics still apply, a PCV on a dry sump is relatively worthless from a emissions standpoint. Hence the proper action post-inspection is to restore to Caterham spec (manifold port capped!). In my case, ref glanced at PCV and 'ticked the box'.

[MV8]

The physics are one vents to the atmosphere through the catch can while the other burns the vapors. The effectiveness is "tunable" for the application with an orifice/restrictor and the box remains checked.

 

For an efi system with an IAC that uses rpm feedback, the rpm increase from the pcv flow at idle should be offset by the ecu reducing flow through the IAC.

 

[rider]

@MV8, @ralph: Sorry, I'm not technical, at all! Is PCV, Positive Crankcase Ventilation? (Had to look up) Is this something I need to mess with on a regular basis? I'll have my car (420R) maintained by a local shop. Thanks.

 

[ralph]

(disclaimer: I'm not technical either)

 

@rider Yes, PCV = Positive Crankcase Vent, and you may not have one on your car (420R kit doesn't come with one, and your state doesn't require it -- CA does).  If you do have one, I'd suggest you remove it. 

 

Follow the oil hose out of the crankcase on the top/right/rear of the engine, and you should see it terminate at the sump tank; in the same general direction, you'll see a hose exit the top of the sump tank and go into a plastic catch bottle; from there the cap of the plastic catch bottle has a hose in it that, in the standard set up, goes nowhere (i.e. vents vapor to ambient air, fluids (oil) to ground -- though the latter shouldn't generally happen unless you have way too much oil in the engine and/or the cap hose is too low in the bottle). 

 

In the setup that will support getting your car registered in CA, that cap hose has to connect to a one-way pressure actuated check valve (the PCV) which connects to the port in the bottom of the plenum.   This 'circuit' is intended to take any crankcase blow-by vapors and feed them back into the engine where they can be burned completely, thus reducing emissions.  In other engines, this can work well.  In our dry sump Duratecs, on the other hand, it can confuse the ECU (increasing idle, which means more emissions), and can make the engine run rough (also increasing emissions with incomplete burn), and in extreme cases (as in mine, as it happens), can even feed a bit of oil into the air intake, which is most definitely not good for emissions.  You could say that the PCV circuit itself is a metaphor for the regulations that mandate it:  excess tax revenue (blow-by) is routed through regulatory apparatus (PCV) in a manner that makes the economy run rough and smell bad while more than defeating the intended purpose.  

 

You can tack this whole thing onto the epically long list of well-intentioned but hopelessly confused CA environmental regulatory claptrap, but if you want a legit registered car in CA, the PCV has to be there.  

 

 

[MV8]

1 hour ago, rider said:

@MV8, @ralph: Sorry, I'm not technical, at all! Is PCV, Positive Crankcase Ventilation? (Had to look up) Is this something I need to mess with on a regular basis? I'll have my car (420R) maintained by a local shop. Thanks.

 

A pcv valve is essentially maintenance free and been installed on most four wheeled vehicles from about 1966. No need to add one or remove it.

 

I think the main regulatory issue stems from folks tasked when ensuring there is a positive crankcase ventilation system, which does not always require a PCV valve in order to be compliant. Just running the drysump vent tank hose to between the air filter and the throttle body would be a pcv system with no valve. I think motorcycles have had this type of system since the mid-70s.

[rider]

Thanks a lot for great details, @ralph and @MV8; appreciate it. I've documented these details. My plan is to register the car in CA first then transfer to MN; I'll have a separate thread on the reg topic. This PCV thingy sounds tricky; will need to make sure it gets done right during the build. I'm guessing if it's a Factory Build, Caterham wouldn't have this in, and the powertrain installer will need to add this as part of finishing up the build?

 

Thanks again.

 

[ralph]

That's correct.  TMK, Caterham does not ship a PCV with dry sump duratec engines; the powertrain installer would have to source (no biggie, it's a <$10 item) and install one (also no biggie -- couple of bits of hose and a couple hoseclamps, maybe a reducer/coupler).

 

For registering cars in CA, the SB100 process is the preferred path, and I'm not sure that's a shorter less complicated/expensive one than registering straight away in MN.  I'm out of my depth here, so I won't say more, but, were I in your shoes, I'd investigate both options very thoroughly...(as you say, separate thread)... 

[rider]

Ok, thanks. Will take note of this. As for the registration, will start a thread and tag you for ideas. Let me dig into it in the meantime.