RV8 crankcase breather pipe

[AntonyJ]

Why does the crankcase breather pipe T off to the plenum base as well as to one side of the butterfly?

Does it need to go back into the inlet side or can it be fed off some where else?

[GreenV8S]

The small pipe goes in downstream of the throttle via a restrictor and provides positive crankcase ventilation under part load conditions. The restriction prevents the full manifold depression from being applied to the crankcase and is designed to be roughly balanced with the crank case air inlet on the opposite rocker cover. The larger unrestricted pipe goes upstream of the throttle and provides a passive ventilation system for full load conditions. It's a cheap low tech way of getting away without a PCV check valve.

[Pupp]

GreenV8S said:

The small pipe goes in downstream of the throttle via a restrictor and provides positive crankcase ventilation under part load conditions. The restriction prevents the full manifold depression from being applied to the crankcase and is designed to be roughly balanced with the crank case air inlet on the opposite rocker cover. The larger unrestricted pipe goes upstream of the throttle and provides a passive ventilation system for full load conditions. It's a cheap low tech way of getting away without a PCV check valve.

Pete, you've probably played with pretty much all permutations on the breathing side. Any experience of what the effect are of not having the little mushroom inlet you refer to. My rocker covers don't have one but have everything else that's 'normal'. The engine has always been a tad smoky and I suspect this might be one reason (usual mechanical causes are not susupected save possibly for guides 'though the stem seals are fresh)

[peaktorque]

Pupp said:

Pete, you've probably played with pretty much all permutations on the breathing side. Any experience of what the effect are of not having the little mushroom inlet you refer to. My rocker covers don't have one but have everything else that's 'normal'. The engine has always been a tad smoky and I suspect this might be one reason (usual mechanical causes are not susupected save possibly for guides 'though the stem seals are fresh)

My smokey RV8 was caused by worn valve guides.

Just ended up changing the both heads in the end.

[spend]

Pupp said:

...Any experience of what the effect are of not having the little mushroom inlet you refer to. My rocker covers don't have one...

I've seen plenty of TVR's with the unused lead retainer screw holes left open which will likely do the same thing, just not filtered or with the one way valve (which many doubt exists anyway after poking it out )

[GreenV8S]

Pupp said:

Pete, you've probably played with pretty much all permutations on the breathing side. Any experience of what the effect are of not having the little mushroom inlet you refer to. My rocker covers don't have one but have everything else that's 'normal'. The engine has always been a tad smoky and I suspect this might be one reason (usual mechanical causes are not susupected save possibly for guides 'though the stem seals are fresh)

The crankcase pressure is controlled by a balancing act between the PCV system, the blow-by past the pistons, and that little air intake valve on the rocker cover. The amount of suck from the PCV system varies dramatically with throttle obviously, the blow-by varies too but in the opposite direction and also depends on the state of the engine. So the pressure goes all over the place anyway.

The air intake helps stabilise the pressure and stopping it going too low in overrun conditions, and by pulling fresh air through it also dilutes the crank case gases which probably helps reduce acid build-up.

So it seems like a good idea. But it's not essential. I don't have an air inlet on mine either (I needed that bit of space for something else) and it doesn't seem to be doing any harm. Most of the ones I see look as if they haven't been replaced for years and are probably gunged up anyway.

[spend]

IMHO unless you look under the valley gasket you don't see the full picture. I have heard of some low mileage engines with modified breathing that frankly look disgustingly black and horrible, compared to my beautiful golden sheen . It might be argued that it's the oil... but personally I'd rather stick to making sure the Rover breathing system worked properly, just in case.

[Pupp]

spend said:

my beautiful golden sheen...

Patience; they're on the way...;)

[AntonyJ]

Thanks for the replies guys, another question now, does anybody have a spare set of the pipes and T piece going spare?

[trakkies]

Dunno if this helps, but the air passages in the plenum next to the butterfly where the breather pipe goes into gets blocked.
To clean, remove the steel pipe the hose fits on to (it's a push fit and can be twisted out - but protect from crushing etc when using grips) That then gives access to the airway via the hole which is at right angles to the pipe. Use twist drills turned by hand or a very slow drill - start with one rather smaller than the passage and work up to a good fit. You'll be surprised how much gunge comes out. This usually clears the small passageway into the actual air intake - but poke it through with some wire to be sure.
When replacing the steel pipe make sure the hole in the side lines up with the passage. Marking the pipe with a Magic Marker helps know where it's pointing.

[AntonyJ]

BUMP !

My engine didnt come with the Landrover pipes and restrictors and after ringing around the T piece restrictor is silly money.

SO, any reason why I cant fit an inline PCV check valve, feed it in upstream of the butterfly and then blank off the small pipe that would go the plenum base?

OR can the breather just be vented to a catch tank? This is recommended in How to Power Tune Rover V8 Engines for Road and Track By Des Hammill

[GreenV8S]

AntonyJ said:

BUMP !

My engine didnt come with the Landrover pipes and restrictors and after ringing around the T piece restrictor is silly money.

SO, any reason why I cant fit an inline PCV check valve, feed it in upstream of the butterfly and then blank off the small pipe that would go the plenum base?

OR can the breather just be vented to a catch tank? This is recommended in How to Power Tune Rover V8 Engines for Road and Track By Des Hammill

You could make your own restrictor quite easily, it's only a T piece at the end of the day.

You can simply connect the large diameter breather hose upstream, of the throttle (as currently) and not bother with the smaller one that connects downstream. This means it's a passive breather rather than PCV but t's not the end of the world.

Alternatively, connect the large breather *downstream* of the throttle with a PCV check valve. This gives you a positive crankcase ventilation system that works properly, it would be better than the original restricted version. Connecting your PCV check valve *upstream* of the throttle wouldn't work - there's no depression there.

If you want maximum performance or just a simple reliable system, you would be best to connect your breather to an external catch tank and not plumb it in to the intake at all. Putting crank case gases back into the intake is bad for the engine, the only reason to do it is to reduce emissions.

[AntonyJ]

GreenV8S said:

AntonyJ said:

BUMP !

My engine didnt come with the Landrover pipes and restrictors and after ringing around the T piece restrictor is silly money.

SO, any reason why I cant fit an inline PCV check valve, feed it in upstream of the butterfly and then blank off the small pipe that would go the plenum base?

OR can the breather just be vented to a catch tank? This is recommended in How to Power Tune Rover V8 Engines for Road and Track By Des Hammill

You could make your own restrictor quite easily, it's only a T piece at the end of the day.

You can simply connect the large diameter breather hose upstream, of the throttle (as currently) and not bother with the smaller one that connects downstream. This means it's a passive breather rather than PCV but t's not the end of the world.

Alternatively, connect the large breather *downstream* of the throttle with a PCV check valve. This gives you a positive crankcase ventilation system that works properly, it would be better than the original restricted version. Connecting your PCV check valve *upstream* of the throttle wouldn't work - there's no depression there.

If you want maximum performance or just a simple reliable system, you would be best to connect your breather to an external catch tank and not plumb it in to the intake at all. Putting crank case gases back into the intake is bad for the engine, the only reason to do it is to reduce emissions.

Cheers Pete, think I will just vent it to a catch tank then, simpler all round.

Also wouldnt need the flame trap internals would I?

Edited by AntonyJ on Thursday 12th February 20:34

[GreenV8S]

AntonyJ said:

Also wouldnt need the flame trap internals would I?

Not absolutely critical but worth keeping since it acts as an oil separator and may reduce the amount of oil carried out into the catch tank.

[Steve_D]

Pulling a vacuum on the crankcase has benefits.
It will reduce any tendency for oil leaks.

Many of the books on Chevy engine tuning claim that for race engines they actually fit a vacuum pump to pull even more vacuum on the crankcase and claim HP gains from doing so.

Steve

[GreenV8S]

Steve_D said:

Pulling a vacuum on the crankcase has benefits.
It will reduce any tendency for oil leaks.

Many of the books on Chevy engine tuning claim that for race engines they actually fit a vacuum pump to pull even more vacuum on the crankcase and claim HP gains from doing so.

Steve

These PCV systems only work off manifold depression though so are completely ineffective at WOT where you might appreciate power gains. You're also going to want to keep the crank case depression quite low (unless you have built your engine specially to cope) since too much pressure difference either way can cause trouble for seals and gaskets.