Hello, I have attempted to search and read all applicable crankcase ventilation content I could find on this site. Very informative! I am building a GEN 1 SBC small displacement engine purpose built for a roots-style blower. I am using a TBS 6v-71 blower. I have constructed a deign for a crankcase ventilation system below. I do not have an MAF sensor. I do not want to use a PCV valve. I think I have this setup correct. Please comment on the functionality of this system. Your time and consideration is much appreciated! No PCV valves used When the supercharger makes boost, a PCV valve could be forced shut This could effectively close a crankcase ventilation system Route hoses from open fittings in the rear of each valve cover to a “Y” connector Baffles must be used inside valve cover openings, below fitting In-line check valves used to limit directional flow out of engine Route a single hose from outlet of the “Y” connector to an air/oil separator inlet Connect air/oil separator outlet to breather tank inlet Valve covers vent through the air/oil separator, and then through the breather tank Allows the engine to breath freely while containing any oil that may be drawn up through the system Route a single hose from breather tank outlet to fuel pump block-off plate fitting In-line check valve to limit one-directional flow into engine Returns a combination of filtered crankcase air and fresh air back into the engine
Strangely enough, A PCV works just fine as it is above the blower. If you don't like the looks of a regular PCV, you can get an inline version that is much more presentable. -Abone.
Here is what I ran for years with a TBS blower on a 355" with 8lbs of boost. Used 1 puke tank on each side of the firewall, with a balance hose connecting both. Worked well for me.
Thanks, Bob. I missed that when you posted this pic in another post topic. So are these simply breather tanks? One side would pull contaminates from the engine and the other side would flow clean air to the engine? And no PCV? Did you get any oil ac***ulation in the pull tank?
Jim, on this motor I did not use a PCV set up. Just vented the crankcase pressure to the dual puke tanks, on one each side from each valve cover. I did not have any unusual oil ac***ulation, and with these tanks they can be emptied if needed. Hope this helps. I wanted a way for the crankcase pressure to exit the motor. On top of each puke tank is a normal breather allowing for the back pressure to exit. It sounds like you do not want to used any type of vacuum to draw it back into the engine like a PCV system would do.
Two concerns... You mention having the 'breather outlet' plumbed back to the motor. Is the breather open to the atmosphere, and the line back to motor is simply a drain, or is it actually the only 'outlet'? If the latter, you've sealed the crankcase and it can't 'breathe' like its supposed to. A crankcase will show positive pressure at some RPMs, negative pressure (vacuum) at others. A standard PCV system works by constantly drawing fresh air into the motor from an external source by using engine vacuum sourced from the intake tract, reducing positive crankcase pressure to atmospheric or a slight vacuum. This takes any vapors and burns them in the normal combustion process. The only reason for the PCV valve is if the crankcase develops too much vacuum, it can draw fuel mixture from the intake into the crankcase, which if it ignites can blow the valve covers/oilpan off the motor. Enough vacuum (and it's very little) and the PCV valve closes, preventing that. This is your 'one way' valve. The system MUST be adequately vented to atmosphere somewhere. Failing to adequately vent the crankcase can lead to leaking gaskets/seals and/or ****ing oil past the rings/valve guides. ***uming you have venting to the atmosphere, I'd lose the one-way valves also; they're not needed. Also make sure there's no place for oil to 'pool' in the lines, presenting a hydraulic 'plug'. Sound like what you're trying to do is prevent any messy oil vapors from getting loose in the engine compartment. I'd suggest a heavily-baffled 'breather box' remotely mounted with a filtered vent to atmosphere. Locate it and all lines so all drainback is 'downhill', when stopped excessive oil will go back to the motor. I built a small unit for a Harley I have, it eliminated all oil dripping out of the air cleaner.
Thanks for the reply. You have brought to my attention some deficiencies in my plan. I am working on a new design that I will post for review. I appreciate your input.
If you connect the PCV valve to the intake manifold, then it could close. If you connect it to the carb, above the blower, then it will be fine. I've put a lot of miles on blown engines with a PCV valve and a breather. The breather installation on a valve cover that does not have a good baffle built in for this purpose, can be a challenge. Knowing what valve covers you intend to use might help us help you figure out how best to do it.
Not sure what I am missing. On every single blower equipped engine that I have built, since 1988, I installed a PCV valve in a valve cover, or lifter valley cover, and plumbed it to a carburetor base. PCV valves exist for a reason, and it is not just pollution mitigation, although that is a good, responsible plan. Catch cans do not accomplish this, and exhaust exit systems can actually push exhaust gases back into the crankcase on vehicles equipped with an exhaust system, rather than an open header. If you think leaving the results of a little blowby in the crankcase is bad, you are not going to like what even a little exhaust gas does to oil. For covers without a baffle, I have had good results with baffled grommets. Otherwise, listen to Jim. He probably has more blown driven miles than all of my clients combined.
JimVG - The crankcase E-vac system to the headers has a one way valve inline down by the collector. It doesn't back flow exhaust into the valve cover (unless it's damaged), it siphons crankcase pressure (and sometimes oil spray) out at speed when blowby is most likely, even when running mufflers. Those systems only draw about 4-5" of vacuum, but will **** oil out of the windage in the valve cover, and right out the exhaust if they're not properly baffled or if there is too much oil splash off the valve train. Don't ask me how I know... There is a HP gain to be had by running a vacuum in the crankcase at high RPM. The oil splash off the crank falls out of suspension easier and the rings seat in the groove better, thus controlling blowby. Some builders actually use a vacuum pump to achieve up to 12" of vacuum. They claim up to 10% gain in power on big inch Pro-Stock motors at 10,000 RPM. Also, crankcase vacuum reduces the pressure on gaskets and seals and lessens the chance of oil leaks. It's a win-win situation, if you can keep the oil where it belongs.
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