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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
I was searching for the parts to put my PCV assembly back on my motor and found the threaded hole on the driver side where the PCV intake hose goes does to appear to connect to the intake..
I purchased this Accel intake to replace the stock but just noticed the hole for the PCV intake hose ends in the cavity and does not appear to connect to the lower intake for vacuum.
I removed the small allen head screw from the top and tried using thin wire to confirm this opening connects to the intake and will pull a vacuum but it appears the machining was not fully completed.
It has threads for the nipple to screw into the intake manifold but if it "does connect" to the intake runners, the PCV will not work.
I really don't want to take the intake off, looking for suggestions especially from someone who has an old intake that can confirm where this hole connects into the intake. Top view Side view PCV threaded hole, close up.
If that hole was never machined through , still and tap the plenum to get manifold vacuum the passage is at the 90 ge green and was made through the 1/8 npt plug on the side iirc.
Last edited by Tuned Performance; 10-21-2022 at 08:15 PM.
Yes, the green arrow slightly tilted up has a passage to the unused "9th injector" recess. I was able to run a thin wire between the two to confirm the connection.
Thanks for pulling me back from the ledge. I was using my pick around the bottom, not thinking it would be in the upper left side of the hole.
You have have earned your name as "Supreme Member!"
I really need to get this monster fired up by year end so cannot afford to go backwards.
The PVC intake pipe is a mockup, need to create the final product in aluminum or steel.
Usually I use cardboard but in this case needed a rigid shape to incorporate where the blow off valve would feed back into the intake.
Agree it would not stand up to the heat and way too thick.
I prefer pulling the air from the front fender verses the stock air cleaner over the header exhaust.
1. I recommend taking a intake manifold source and running that through a 1995-1998 Toyota Twin turbo supra PCV valve and from there into 1 valve cover
2. Take the other valve cover and attach it to the intake post-maf , pre compressor, just like all factory forced induction vehicles, thus completing the OEM PCV system
A. if you use a stock pcv valve it will leak boost into the crankcase causing oil leaks, ring flutter, blow-by, etc... not good
B. Without The hose connecting crankcase to pre-compressor you will not have PCV Under boost, which will fill the crankcase with blow-by, contaminating oil, leading to deposits and eventual wear and failure, and it will also cause ring flutter, blow-by, poor sealing rings, oil leaking, etc...
Finally after you connect these you must perform a pressure test to find all leaking boost and test the PCV system. Air pressure from compressor should be put into the compressor inlet and fill the entire plumbing, intercooler, intake manifold etc..
And I also recommend measure the crankcase pressure at WOT to ensure the pcv system is working. You can use a 5v source to power a MAP sensor, 1-bar map is fine, find the baseline voltage say 4.54v or 4.27v or whatever, then watch it under boost it should go down roughly .1 to .25v from baseline on the crankcase.
If you need videos of these pressure test and how to measure crankcase pressure I can supply it
Thanks for the recommendation. I have had some experience with PCV blow by on a Supercharged Bronco which required oil catch cans installed between both the PCV fresh air intake hose and hose between PCV and intake manifold to capture the sludge before it went back into the engine. The fresh air intake side had minimal sludge clean but the hose between the PCV and intake had 1/4 cup of sludge per week that had to be cleaned out.
I've attached the PCV diagram for my 1989 IROC to base line how it works naturally aspirated. The PCV (purple) draws vacuum from the lower intake which creates a vacuum through the engine by pulling air in from the fresh air intake hose (green) on the other valve cover. This fresh air hose is attached to the Throttle body (blue) which see's vacuum at idle and little vacuum at WOT. Either way, the PCV will always have more vacuum from the lower manifold sustaining vacuum in the engine.
Under boost: The throttle body, upper & lower intake will be pressurized. The fresh air intake hose (green) is going to pressurize the engine crankcase. To avoid this, I should remove the fresh air hose from the Throttle body (green) and attach it after the MAF and before the Turbine inlet on the SC which would prevent the fresh air hose from being pressurized unless the PCV (purple) fails on the other valve cover. The hose from the lower intake to the PCV (purple) will be pressurized but should not pass into the engine crank case due to the check valve in the PCV preventing air/gas from going backwards. You recommend using a Toyota PCV (used on SC engine) which is superior to block the pressure from getting into the engine crank case.
My only concern with this approach is if the fresh air hose is connected between the MAF and SC turbine inlet, at idle I can see the vacuum of the engine over coming the vacuum of the SC Turbine inlet but not at full boost. The vacuum at SC Turbine inlet at full boost could suck air/gas in reverse direction inside the fresh air intake hose (green). The upside affect is the crank case would still be under vacuum but the downside could be oily sludge getting sucked into the SC Turbine intake.
At idle and during engine cruise/vacuum condition, air flows from the pre-throttle body into the engine crankcase, and then from the other side of the valve cover into the intake manifold through a PCV valve. It is this throughput, from one side to the other, which keeps the crankcase clear of blow-by gas and prevent interaction with engine oil and sludge forming. During idle and cruise the pre-throttle body does NOT see any vacuum like you suggest. Just like the region in front of the compressor wheel will not experience any vacuum at idle or cruise.
The reason is because the air filter has no pressure drop during idle and cruise. Air filters only pressure drop near their max rating, say 1.5" Hg at 500CFM or whatever. The pressure drop for a 500CFM @ 1.5" Hg at idle is 0.0001" Hg at 80CFM for example.
Next, the oil should not be sludgy. That means the PCV hasn't been working and now the engine is full of sludge and needs to be cleaned or rebuilt. A clean engine has clean oil, not sludge, and clean oil which interacts with the PCV system components is fine. It will lubricate the compressor wheel and improve mileage and reduce wear for the compressor wheel. The engineers of turbochargers and superchargers intent for a light oil film to interact with and protect the compressor wheel, it is beneficial. If you'd like I can provide direct quote from the manufacturer or you can ask yourself. Even so it is very little oil and I Recommend hit the wheel with WD40 now and then to keep it from oxidizing due to high rate of incoming airflow that attacks metal materials.
Under boost:
Right, the pcv valve is going to fail if you are using a chevrolet. It will not work. If you pressure test you will see this. That is why the engine blows oil out and fills a catch can in your other engines , the PCV valve was not sealing up because it needs a PCV valve from a turbocharged engine like the Supra to seal properly.
Under boost the supercharger will create a pressure drop between the air filter and compressor wheel ,just like the natural aspirated engine does from all engines in the world, it will pull about 1" Hg or so depending on the air filter pressure drop. Whether N/A or turbo or supercharged makes no difference; it is the air filter's job to provide this pressure drop which allows this section of pipe to pull on the engine crankcase scavenging blow-by gas at wide open throttle. If the pressure drop is correctly at least 0.5" Hg there will not be significant oil induction as long as the engine is healthy, it will be a barely light coating of oil residue over the course of 40,000 miles or so. This is how all forced inducted factory engines are able to maintain PCV for 250,000 miles, for example Supra twin turbo uses this exact PCV setup and those engines last for 250,000 miles 25 years so far.
So what's the deal with pressure drop and catch cans, because it seems to me like if you had a closed catch can (does not vent) in both pcv and ccv tubes, you'd have the same crankcase evacuation minus the oil particulate reentry.
Lines add friction which kills pressure drop provided by the filter, causing pressure to rise in the lines and leads to increased crankcase pressure.
Can additional volume is added crankcase volume which causes disorganization of PCV flow and also reduce the effectiveness of pressure drop signal, i.e. increased mass to move (more volume) to influence a particular pressure drop target. In other words the larger the crankcase, the more mass you need to move out of the crankcase to start seeing a drop in pressure.
Thus, can and additional lines or even larger lines are unwanted, because they are adding friction or volume or both.
Finally , clean oil is a desirable feature for lubricating metal materials. You need oil on the throttle shaft and compressor wheel to maintain the smooth operation and protect from oxidation etc...
There is nothing about catch cans that is useful unless the engine is broken, blown, e.g. broken piston. This will cause excessive crankcase pressure that the PCV system cannot handle and will boost the crankcase (boost pressure from leaking compression) causing alot of oil to blow out of the engine, you need the can for that situation.
Another possibility is an engine which is used outside of its baffle capability, such as thrashing tight corners high G forces and high volume pumping oil due to higher than factory RPM frequently, flooding baffles with engine oil that does not return to the oil pan fast enough, in this case a temporary solution would be catch can until you can go into the baffle and drill/cut/fabricate to correct the drainage issue and internal oil control
10-21-2022, 08:00 PM
