PCV Yea or Nay

[Iain T]

Following on from another thread I have been pondering the positives and negatives of a PCV. I have recently reconditioned the engine in my MK2 Vitesse and am trying to decide which way to go or do nothing at all and leave as is!

Option 1

Keep PCV and fit a crankcase vent and filter via the fuel pump aperture. This would let the crankcase breath but still let 'nasties' from the rocker into the inlet system and gum up my nice new valves and weaken the AF mixture but then this happens in a standard set up. 

Option 2

Keep PCV and fit a 3-port baffled/filtered oil catch can (Mishimoto compact or XL?) by say the clutch master cylinder (see photo) then plumb to the IN the rocker and crankcase and OUT to the PCV. This filters out some of the 'nasties' but is the PCV big enough to handle the flow?

Option 3

Ditch the PCV and blank the inlet manifold connection. Fit a 3-port baffled/filtered oil catch can in position as Option 2 with the rocker and crankcase pipes to the IN and a filter to atmosphere in the OUT. This removes all 'nasties' in the intake system and vents the whole engine. I believe John has this setup? This does not vacuum assist the system at idle but is that important if the rest is adequately vented and the carbs set up to suit?

Option 4

Do nothing and leave as OE

As originality is not that important to me I am inclined to go for 1 or 2 but am open to suggestions!

Iain

PS

Yes I know I still have the K&N's as I haven't made my new Chris Witor style airbox!

[Nigel Clark]

If it was me, I would stick with the standard PCV unless the engine is trying to blow its oil out (like my TR6 was, if that's the other thread you mention). Generally the PCV works well, allowing some vacuum scavenging of the engine.

Nigel

[Pete Lewis]

+1 for leave as is , does what it says on the tin , unless theres a breathing problem  save the £££ buy fuel   drive car 

Pete

[Iain T]

Thanks for replies I did clean out the PCV and replace the diaphragm when reconditioning the engine.  Pete I would drive the car if I had somewhere to go that was open and had a toilet! Sooon very soooon😁

Still there's going to be fields full of non PC statues for us all to visit soon! Sorry I'm incandescent over recent events😡 a subject not for this forum. 

Iain 

[dave.vitesse]

+1 Stick with the standard PCV set-up. No sump breather. If you have a sump breather and the PCV because the breather allows air into the engine both air and fumes will be sucked through the engine into the inlet manifold. The whole points of the closed circuit system is that there is no through path.

The open circuit system works by air entering the engine through the sump breather and out through the rocker box breather. 

Dave 

[Iain T]

What about option 2? This keeps the closed system but better vents and filters gases at higher revs or is the PCV aperture and hose sizes the overriding factor making fitting a crankcase vent irrelevant? 

I would prefer to keep the engine bay less cluttered but I think it was Marcus who said the rocker outlet was too small. 

Iain 

[dave.vitesse]

Under normal road use the close circuit system will work OK. The only time the closed circuit is a problem in road use is if the engine is badly worn and producing a high level of fumes internally. 

In the case of a highly tuned engine used on the track then many go for the open circuit system with a catcher tank which works OK.

However, if you are worried about the rocker cover breather on the open circuit system then fit either an early 2000 saloon or Vitesse 6, 1600, rocker cover with a breather oil filler cap.

So - 

1/ Is this road use or track use.

2/ Is the engine badly worn.

Those are the questions you should ask yourself. 

Dave

[Iain T]

Dave, 

The engine has just been reconditioned to a high level ie honed bores, new rings, sorted head with 10.5CR and new higher lift cam etc but only spec'd as a road engine and car. It's just me being paradoid about stopping oil leaks. 

I think I'll park this idea and get on with enjoying the car! 

Cheers🍻

Iain 

[Ian Foster]

Hi Iain

I fitted a catch can to my GT6 just to clean up whatever was being fed back into the engine, as oil content does reduce octane and we need all we can get. I mounted at the front of the inlet manifold as my bulkhead is quite full due to the brake servo and larger washer bottle.

I have retained the original Smiths PCV and as you can see from the photo, the breather outlet from the rocker box to the catch can and then to the PCV which connects as normal into the inlet manifold. The catch anodized alloy can is an ebay special, which came without any internals, so I added an inlet pipe, pan scrubbers and top filter (details available on request if required).

The can does collect a small but useful amount of deposits (probably 1/2 cup in about 3000 miles), which has a definite 'breathery' type smell to it and the PCV internals are staying nice and clean. Presumably better for the environment as well.

Hope this is of interest.

Ian 

[daverclasper]

On 10/06/2020 at 10:29, Iain T said:

Sorry I'm incandescent over recent events😡

I'm the opposite. Better late than never 😊, though your right, probably not for this thread.

Anyway back to cars. My Vitesse was breathing direct from rocker cover to air filter box when I got it. Fitted the standard valve and rocker cover oil leak disappeared, as now had vacuum in that area. Also seemed more consistent fuel mixture through the rev range.

Dave  

Edited June 11, 2020 by daverclasper

[Iain T]

Dave, seems the vacuum in a road car really does work I'll be keeping the PCV! 

Ian, I know I said I'll park the idea but I can't help thinking a filtered/baffled can feeding the PCV must as you say be a better solution. Is the breather external to the can or an internal baffle? If it's a breather it is no longer a sealed system so the intake vacuum won't scavenge. 

Cheers all

Iain 

[Ian Foster]

Hi Iain

My install is a sealed system as the PCV valve pulls through the catch can. It is my understand that air can enter the rocker box via the vent in the cap to partially compensate for the vacuum. The operation of the PCV valve is actually quite complicated and I have an explanation of how it works somewhere, which I will post if I can find it. (Presumably invented by a Mr Smith!)

Seems to work well. I guess catch tanks weren't around when Triumph designed the system, but are very much in favour with the modern tuners.

It would be interesting to know why the PCV was dropped for the later cars...cost perhaps!

Ian

 

 

[Iain T]

Ian 

Modern cars have hi-tech gas recycling systems and sensors everywhere! 

I think the eternal conflict between bean counters and engineers is the reason for many compromised products. Apart from cost I can't see a downside of using a catch tank. 

Iain 

[Colin Lindsay]

15 hours ago, Iain T said:

Modern cars have hi-tech gas recycling systems and sensors everywhere! 

Which is why the Net is full of great articles on how to remove or by-pass them. EGR valve being one such.

[Pete Lewis]

same as no manual refers to  some of the rocker covers with a flame trap gauze  hidden  inside the cover that blocks up  and corks  the breather outlet 

Pete