1996 850 boost pressure into crankcase/ one way valve.

[Sommerfeldt]

I don't know why people would argue there isn't 12 pounds of boost plus blow-by at the PTC diminished only by the small hole in it and
the very slight vacuum present in the intake tube, thus pushing back into the crankcase. any thoughts or experience with a one way valve on the vacuum valve from the intake? I notice there is one on the charcoal canister line off the throttle-body tree. Im not really discussing maintenance issues, just how pressure in the crankcase can be better relieved in what seems an inadequate system under any boost, let alone increased and long duration boost.

Well, there might be 12 psi of pressure in the intake manifold, and so the small "vacuum" line from the end of the manifold to the side of the PTC will in theory see some of that... but the pressure in the manifold is handled by the engine - that's where it's supposed to go (which is also why that little line only needs a rubber elbow and not a clamp of any kind), and the volume that small line carries is pretty minuscule.

The blow-by shouldn't be more than the stock lines can handle, but the main point is that crankcase pressure won't travel back into the block, since there will be positive pressure inside the block, escaping. There won't be more pressure outside the block than inside it. With that in mind, I think a better route is to facilitate that escape. A lot of people replace the stock line to the top of the PTC with larger ID, often also coupled with a catch can (I have one on my '96). There have also been reports of people deleting the PTC all together, but enlarging the hole might also work. The PTC doesn't seem to have a severe impact on much at all, especially if you have a catch can that handles the moisture and whatnots the engine pukes out that way.

- S

[June]

Doesn't the ball in the banjo bolt prevent positive pressure from going backwards through the system? June

[Sommerfeldt]

Doesn't the ball in the banjo bolt prevent positive pressure from going backwards through the system? June

No - it’s the PCV system. No banjo bolts.

- S

[hausmeister]

I think you are wrong about this causing any issue with crank pressure.

But to answer your question: I installed a one way check valve in the vacuum line to the ptc. Reason for this is that I drilled the tiny hole a bit larger during the pcv renewal (also used larger hoses) and I didn't want to lose any precious boost pressure . The valve works fine as far as I can tell (only open during vaccum). Doesn't seem to impact pvc system.

[Klausc]

I don't know why I have to say this, but boost pressures the intake manifold, not the crankcase.

[tardcart]

Hausmiester, now we are getting some where; one, and I thing two good reasons to block pressure to the PTC/crankcase. and a vote to enlarge or eliminate the PTC. I wonder if the heat function of the PTC is to prevent coagulation causing blockage or to pre-heat vaccuum
in non turbo mode? I think the whole system was designed in 93 for na cars and they never bothered to improve it for pressurized intake. Volvo maby used the money to change to five lug wheels.

[abscate]

It is a good design for the turbo. My 1999 was 10% occluded after 160k miles as the car was maintained with 5000 mile oil changes. The PTC heater is to prevent the sludge from condensing in the port.

Opening up the port is fine if you can figure out the mass balance of crankcase air

[Klausc]

I think the whole system was designed in 93 for na cars and they never bothered to improve it for pressurized intake. Volvo maby used the money to change to five lug wheels.

The NA engines do not have a PCT, the vacuum line from the #1 cylinder area goes to the PCV and the intake just before the throttle body.

That same small line is used by the turbo engines to draw air from the large line that enters the PCT, drawing crankcase vapors from the oil separator. During boost, the small line does not produce a lot of air pressure to the PCT which is already under a lot of negative pressure.

The reason for the EVAP system vacuum shutoff is so that the positive manifold pressure (during boost) does not blow out the EVAP system.

[tardcart]

The turbo intake pipe is basically under zero negative pressure if the filter is clean. so I dont think its drawing much from the PTC. thinking it over I guess its best not to enlarge the PTC much since that would lower the vacuum to the crankcase at idle which is important for clean smells at the stoplight. I guess Ill try a one way vacuum valve from the intake manifold and scratch my head about a shunt into the turbo intake from the crank breather that is activated under boost . or maby a blow off valve set at 3 pounds. This is the major drawback that puts these cars in the junk yard; blown seals, just behind over heat issues with bad hoses and heater cores.

[Sommerfeldt]

The turbo intake pipe is basically under zero negative pressure if the filter is clean. so I dont think its drawing much from the PTC. thinking it over I guess its best not to enlarge the PTC much since that would lower the vacuum to the crankcase at idle which is important for clean smells at the stoplight. I guess Ill try a one way vacuum valve from the intake manifold and scratch my head about a shunt into the turbo intake from the crank breather that is activated under boost . or maby a blow off valve set at 3 pounds. This is the major drawback that puts these cars in the junk yard; blown seals, just behind over heat issues with bad hoses and heater cores.

Well, there is negative pressure there - at our FI levels, there won't be much, but some. It's important to note that there is no check valve on the system from the factory, and blow off valves are not a good idea in a system which depends so heavily on MAF metering of all the air that enters it (and thus leaving it). The main problem again, as you also say, is blown seals when internal pressure climbs too high, and providing effective and adequate relief of that pressure.

Providing a larger path to the PTC and having fluids condense and collect somewhere other than the relatively small passages of the PTC and elbows there (not to mention intake manifold) is the best way to ensure that and augment the factory system - i.e. bigger hose + catch can.

- S