VR Engine "breathing" & catch tank systems

Thanks for that excellent info JNLR!

I will be doing a bore refresh (hone and new rings) when I take it apart soon for stronger rods and rod bearings etc.

I've recently noticed compression is down on a couple of cylinders so hope this might restore them..... I don't know if the figures can be relied upon as 100% accurate as it was only a cheapy Gunsons CR tester from Halfords, but it gave me an idea at least.

I've noticed the engine's "breathing" a bit more because there's oil spots all over the rear bumper from the crank case hose (vents down by the steering rack). Oil consumption is still OK and there's no blue smoke, so I suspect the top rings could be worn on one or or more pistons?

83mm Wossner forged piston VR6 block, after 30K's use:-

1 - 170 psi
2 - 185
3 - 190
4 - 185
5 - 170
6 - 185

Pretty much on the money apart from 1 and 5. Not a huge difference I know, but I'm a fussy git

How do I tell if I have to use 30 or 60 deg honing?

[mod edit]Seemed worthy of a separate thread Beigy

Normally compression tester will dictate how well ring 1 seals which is what your results will show. These will vary depending how well they have been gapped and how rich the car runs at normal cruising/idling.
Heavy breathing is caused by an overly worn number 2 ring or a gunked up number two ring due to worn oil scraper rings.
Your oil rings will dictate how much oil your engine burns as it is the barrier that cleans the bores on the downstroke.

A FI engine will generally have more blow by than a standard NA engine due to increased combustion pressures. Leading to accelerated ring wear. This can be compensated for by creating a vacuum inside the crankcase so that there isn't pressure pushing on the rings from below on the downstroke. This is why manufacturers feed the breather back into the intake tract to create this vacuum. To the extend on the later v8's in America they run a crankcase evacuation pump of the belts to help scavenge air from the crankcase as these are more prone to blow by on the rings due to the large bore sizes.

Worst thing you can possibly do to a FI engine is run the breather outlet of the block to atmosphere or a catch tank as the diameter of the breather is not sufficient to create a vacuum in the crankcase.
By routing it back into the intake tract via a proper filtration system, foam filled catch tank that vents to the intake instead of atmosphere you can gain anywhere from 10-15 of power on a FI engine by creating a better piston ring seal and making the pistons work less hard on the downstroke.

Other thing to look at is AFR ratio's if an engine runs too rich then it will borewash putting the abrassive fuel into the oil of the engine. This results in weakened piston rings making it breath real heavy as you start to suffer from mild piston slap.

Re honing angles 60 degree honing is only used when specified by the manufacturer of the piston rings. So as a general rule of thumb anywhere between 30 and 45 degrees is fine for all other rings.

Most sealed vacum systems are emmisions related, as you dont want unburnt fuel an all other nasties going into atmosphere.

and as for less pressure agaisnt the rings,surley the downstoke of one or more pistons is then met by the upward stroke of one or more creating a neutral balance in the motor?,yes there will be pressure in the block but hardly to effect the ring stress and overall life of the motor....?

You would also need the vacum to enter after the throttle to gain any advantages vacum on part throtle/crusing to create positive vacum in the crankcase as entering after (as most/all maufacturs do) will have very little affect and on boost will have positive pressure most of the time right?

Im not saying your wrong but i cant see this 10-15 power gain.

I run my breather to atmosphere,so if i run it back in i will notice an imporvment?

I understand the theory of it. When the motor's working hard, I guess the evacuation process works better if the gases are being sucked out rather than relying on being pushed out?

I suppose venting it back into the intake upstream of the turbo compressor should pull the fumes out quite nicely?

As JNL says, you'd need a very good catch tank system to avoid clogging up the turbo blades, intake tracts and intercooler with oil. And you need to avoid that horrible emulsified water / oil mayo mix getting into the engine, which you get when the crank fumes cool down rapidly, as they would if going into a catch tank or atmos.

The VR6 is quite a breathy engine anyway. Even standard ones line the throttle and the intake with oil. I noticed a bit of that on Kad's R32 engine aswell, although not quite as oily as a typical 12V.

What to do eh?

Sorry Kev the VR does not breath heavy at all imop,unless its fu*ked,not compared to most four cylinders,seen what it has for a breather/catch tank,not much and it still breathes low.

What about on boost? surley there is more pressure than vacum at theses levels?

Yes but you have a brand new engine, of course it's not going to be breathy....yet. You can't tell me that all the oil in the intake on 60K plus old VR6s isn't breathy?

The missus 1.8T has hardly anything in the intake and throttle so I don't buy that, sorry.

Yep, loads of pressure on boost, hence the crank fumes blasting built up oil in my vent hose out under the car, and sticking to the bumper.

Maybe my 2nd rings are shagged as JNL says, I'm not discounting that and I'm certainly up for trying a decent breather system.

im not having a go Kev ,yes my motor is new,but my old motor at 155k was an easy breather.

Your missus 1.8t has a superiour breather system compared to the old 12v.

Im not saying the VR breather system is ideal but a good catch tank will help,i have no doubt in that.

anyway.....i need a drink on sat night...why am i still here

similar discussion went down on this Honda forum with someone testing all the methods

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and a pistonheads thread with regards to the gains to be seen can be found here

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The biggest issue I've had using the exhaust system setup is it doesn't like FI engines as the one way check valves melt from exhaust temp causing crank case pressurising instead. The most effective system is using a dry sump setup which will remove air bubbles from the oil at high rpm and carry out your crankcase evacuation at the same time.

Can you recommend a decent catch tank system for FI use?