Hello all, I have some questions about crankcase ventilation with a boosted engine. Perhaps those who have boosted setups can help! After researching online it seems best to set up two crankcase vent systems, one for when the engine is under boost and one for the engine under vacuum: Vacuum (off boost) - Baffled PCV valve goes from valve cover to oil separator to intake manifold. Boost - PCV valve closes from boost. Baffled tube or breather from valve cover goes to 2nd oil separator and then into the turbo’s air intake. Vacuum from the turbo pulling air will also pull in crankcase gases. Does this sound like it would work? I’m looking for a setup that I can run on both the street and the road course! Will the turbos get messed up form injecting oil-free crankcase gases? The reason I’m thinking about this now is because I’m about to start drilling holes into my nice Poston valve covers for the oil cap, PCV, and/or breather and I want to get the positioning and hole size figured out. That all depends on my crankcase ventilation setup!
Yeah, it has to be different because of the turbo and increased blow by. How do they do it in the GN? Some discussion on this other board, https://www.thirdgen.org/forums/power-adders/462719-pcv-turbos.html
Larry beat me too it, yes go search the Turbo Buick forum/s This has been an ongoing issue/discussion for years. I do know Buick used a specific PCV valve for the Turbo Buicks because a turbo engine operates at LESS vacuum under all conditions than a Naturally Asperated engine does, as the turbo is always spinning creating a condition of "less than usual" vacuum, until its spinning fast enough to create positive pressure in the intake manifold. My GN only creates around 10-12-14" of vacuum at highway speeds verses my GS which creates around 18-22 at highway speeds.
I've tried several things on my blower setup with mixed results. Usually controlling the idle speed ends up being the big issue. Now what I use is a dual system. I have a small line from the valve cover to the intake plenum which has an orifice. It should probably have a check valve as well and I plan to look at that. But, for now it pulls a measured flow from the valve cover and there is a small inlet filter on the other valve cover. Under boost it undoubtedly backflows which is why a check valve would be a good idea. (Note: a PCV valve is a spring loaded orifice/check. It does flow both ways.) The second part of this system is a vacuum controlled 5/8" (may be 3/4") heater valve which closes on application of vacuum. This connects to a flame arrester screwed into the first valve cover. It is plumbed to the blower inlet behind the air filter. So this is how the system works. At WOT the heater valve opens directly from the valve cover to the blower inlet. (The throttle body is at the inlet opening and the main air filter is behind that.) Undoubtedly a small percentage also flows out the small inlet filter on the other valve cover but due to the pressure drop across the main air filter most of it goes into the blower inlet. At cruise the valve is closed or partially cracked depending on power levels. Flow is all through the small line up to the cracking pressure of the valve. Because I run Speed/Density the mixture is dependent on MAP so this has no effect on the mixture, or very little which is accounted for in the tune. At idle flow is through the small line only. The maximum size of this orifice and line is dependent on factors such as desired hot idle speed, the fit of your throttle plates and other points of leakage. Jim
This is excellent info! I too was thinking about trying to incorporate a heater valve into my system so that the turbo inlet side only functions under boost. The only thing I couldn't figure out was how to make the heater valve open under boost. Most seem to be "pull to open" meaning that when vacuum is applied too the diaphragm the valve opens. I would need one that opens when boost is applied to the diaphragm, or to modify a normal one by moving the diaphragm. I was going to run a check valve in the PCV line as well. Here's my idea: What do you think?
Almost there. Put your PCV or check valve line on the same cover as the big vent line (with the heater valve) and a small air filter on the other to get flow-through ventilation. Or you can plumb that line (minus the small filter) to the inlet behind the main air filter. In fact with that setup you really do not need the heater valve and line. The only reason I used it is because my air filter is between my throttle body and my blower inlet so it sees full vacuum at idle. If your filter is before the TB you can plumb it in there and don't need the valve because it never sees full vacuum or boost. It will vent blowby into the inlet under WOT and the smaller line will handle part throttle with the standard PCV. Flow will reverse at part throttle and draw filtered air in from the large line. That is the way the stock system is designed and there is no real need to deviate if you can plumb it to the right spot. Very important, you do have to have flame arrestors, especially on the large line, otherwise you can have a crankcase explosion. (BTDT) The PCV valve serves that function in the small line. OEM used filter media at the large hose/filter housing attachment, in fact they ran the blowby into the filter housing outside the main air filter and thus ran the blowby through the filter on the way to being burned again, thereby reducing the fouling of throttle plates and such. Rover used a canister filled with brillo. (brass or steel scrubber pad) I use the screw-in Rover part. A catch can may serve that purpose, but only if it has a flame arrestor built in. So for your drawing, I'd use a PCV in place of your check valve, eliminate the catch can in that line, eliminate the heater valve, make sure there is a flame arrestor in that line, and vent it ahead of the throttle body. If that isn't possible, Then use the modified system with both the small air filter (valve cover vent) and the heater valve. Plumb the heater valve and PCV to the same valve cover and the small air filter to the opposite. If a check valve is used instead of the PCV, be sure to put an orifice in this line to restrict flow at idle and act as a flame trap. Make sure there is a flame trap in any line leading to the induction system. Jim
Awesome info Jim! I'm still working on decoding it and drawing another diagram haha. Can anyone explain if there are any disadvantages to using just vents? Besides maybe being more messy?
Try not to over think this or get to complex. Your not in boost all the time, your going to be in a vacuum state most often. Find out what kind of vacuum your pulling cruising on the highway, at idle and city driving. Use an air/oil separator between vacuum source and PCV valve.
I asked a few friends and it sounds like most guys are doing a 10 AN line from each valve cover into a catch can with a breather.
The purpose of the pcv valve is to burn the blowby. Since most of a street driver's use is at idle and part throttle, most of its life there is vacuum available, either at cruise or idle. The valve's purpose is to differentiate between the two and still provide adequate suction to keep oil vapors from depositing in the engine compartment. So yeah, you can rely on one or more breathers, and a catch can if you don't mind servicing that, which is fine for racing, but if it's your daily driver why would you? Route your vent lines so they self drain back into the engine, make sure the lines are big enough to handle the maximum blowby, and let the engine handle it. Factory engineers were on to something with this system. It was a very big deal when it first appeared and was well done. The only real issue with it is that as you increase power you also increase blowby volume so the large vent line needs to get bigger and sometimes multiply. Jim
That's what I did. Except I used a piece of hydraulic line on each side and made it go upward as far as possible and then the downward direction was set to burn off on the exhaust. With such a long ways going up, I don't think any ever drained down to burn off.
1920's technology but it worked. Engine life suffered , oil change intervals were much shorter, and we had black snail tracks down the middle of each and every traffic lane, (go look at old photos) but you just stayed away from that when it rained. Jim
