I'm putting in a supercharger and I came across this thread:
PCV 101 for Forced Induction 80's
Basically, it suggests that the PCV routing should be changed from the TRD instructions so that the PCV hose moves from the intake manifold to the throttle body adapter pre-supercharger. Unfortunately, the explanation of the mod is somewhat hard to understand especially given all the arguing thread. So, I've spent the last week or so trying to understand the 80's PCV system and whether to do this mod or not.
So what does a PCV system do? PCV stands for Positive Crankcase Ventilation. It's basically just a system that relieves pressure from the crank case. Pressure builds up as the engine runs because there's always a little blow by around the piston rings and makes its way into the crank case. Back in the day, this pressure and the associated vapors were just vented to the atmosphere. Modern engines bleed the pressure to the intake manifold where the vapors are sent back to the cylinders for another chance at combustion. If you didn't bleed off the pressure it would cause engine oil seals to leak and sludge to be created.
How does it work? Basically, it's just two tubes and a check valve. Clean air comes into the valve cover through the breather tube, it travels through a baffle under the valve cover that condenses some of the oil vapor back into the crank case, and goes out through the PCV valve into the intake manifold. Pretty simple. Here's what it looks like on the stock engine.
What does the PCV valve do? The system works because vacuum is created in the PCV hose as air is pulled through the intake. This causes air to flow from the breather to the manifold. The vacuum varies depending on the state of the engine. When idling, vacuum is very high. At wide open throttle it's pretty low. This is the opposite of what you want. At idle, there's not much blowby and not much crankcase pressure. If you pulled on it with a strong vacuum you'd suck a bunch of oil into the manifold. At wide open throttle you need to vent more, but you have less vacuum. The PCV valve is basically a spring loaded valve that changes how restricted the PCV line is depending on the vacuum applied to it. Here's a diagram of how it works:
So why's there a problem with a supercharger? First, here’s what the PCV routing looks like with the supercharger. You can see there really isn’t any difference. The PCV line is unchanged. The breather line is unchanged too, despite the fact that throttle body has moved. It goes from the same spot on the valve cover to the same spot on the throttle body. The only difference is that the breather line is still pre-supercharger while the PCV port is now post-supercharger.
The stock setup works because there's vacuum in the PCV line. If you pressurize the intake manifold with a supercharger, this goes away. At idle and probably under normal load, the system probably operates about the same because you’re not boosting much if at all. However, at wide open throttle there is boost which pressurizes the intake manifold. So, the PCV operation changes to this with a supercharger:
Why is this a problem? Basically, when running full out with forced induction, the PCV valve will close and won't be venting the crank case anymore.
What will happen? Well, I don’t really know for sure. I suspect what will happen is that because the breather tube doesn’t have any type of valve on it, the crank case will vent through the breather tube. So, instead of pressure and vapors going directly to your intake manifold, they’ll instead go through your throttle body, supercharger, and eventually reach the blower. Also, because no fresh air is coming in, you probably won’t do as effective a job at moving the bad vapors from the blowby out of the crankcase. However, some claim the crank case will build up pressure and start compromising the oil seals in the engine. I don’t see how this is possible. You may build up a little more pressure than normal, but you’re still venting pressure out the breather so it’s not like the engine will build pressure forever.
However, there is the possibility that the PCV valve fails open and you begin losing boost into the crank case. I suspect that if this happens you’ll probably start blowing a lot of oil out the breather tube and will start seeing something like this:
https://forum.ih8mud.com/threads/sc-and-oil-inhalation.911482/
So what is this mod all about?
https://forum.ih8mud.com/threads/pcv-101-for-forced-induction-80s.150299/
Basically, to do the mod, you route your PCV hose from the intake manifold to a port on the throttle body adapter. This puts your PCV hose pre-supercharger but post throttle body.
Essentially, this makes it exactly the same as the stock normally aspirated setup. You should always have vacuum on your PCV hose with this setup and it should work similar to stock form. The downside is that you’re now always venting through the supercharger. All the oil that typically builds up in the intake manifold will now be building up in your supercharger. To some extent this is probably already happening under boost for reasons I explained earlier, but with this mod it happens all the time. The advantage is that if your PCV fails open, there’s no chance of boosting the crank case and blowing out a lot of oil.
So is it recommended or not? In my opinion, both systems should work fine. If you keep on top of your PCV valve there’s really not much problem with the routing in the TRD instructions. I went into this research thinking I would do it, but after understanding the whole system, I don’t see much advantage. I’ll just make it more of a point than normal to pre-emptively replace my PCV valve.
One other point I’ll raise is that with the TRD recommended routing, a catch can on the breather hose might be beneficial if you really don’t want anything being vented through the rotors.
Anyway, hopefully this is a clearer explanation of what that mod is all about and what is going on with the PCV system when you supercharge. Hopefully I didn't make too many glaring errors.
PCV 101 for Forced Induction 80's
Basically, it suggests that the PCV routing should be changed from the TRD instructions so that the PCV hose moves from the intake manifold to the throttle body adapter pre-supercharger. Unfortunately, the explanation of the mod is somewhat hard to understand especially given all the arguing thread. So, I've spent the last week or so trying to understand the 80's PCV system and whether to do this mod or not.
So what does a PCV system do? PCV stands for Positive Crankcase Ventilation. It's basically just a system that relieves pressure from the crank case. Pressure builds up as the engine runs because there's always a little blow by around the piston rings and makes its way into the crank case. Back in the day, this pressure and the associated vapors were just vented to the atmosphere. Modern engines bleed the pressure to the intake manifold where the vapors are sent back to the cylinders for another chance at combustion. If you didn't bleed off the pressure it would cause engine oil seals to leak and sludge to be created.
How does it work? Basically, it's just two tubes and a check valve. Clean air comes into the valve cover through the breather tube, it travels through a baffle under the valve cover that condenses some of the oil vapor back into the crank case, and goes out through the PCV valve into the intake manifold. Pretty simple. Here's what it looks like on the stock engine.
What does the PCV valve do? The system works because vacuum is created in the PCV hose as air is pulled through the intake. This causes air to flow from the breather to the manifold. The vacuum varies depending on the state of the engine. When idling, vacuum is very high. At wide open throttle it's pretty low. This is the opposite of what you want. At idle, there's not much blowby and not much crankcase pressure. If you pulled on it with a strong vacuum you'd suck a bunch of oil into the manifold. At wide open throttle you need to vent more, but you have less vacuum. The PCV valve is basically a spring loaded valve that changes how restricted the PCV line is depending on the vacuum applied to it. Here's a diagram of how it works:
So why's there a problem with a supercharger? First, here’s what the PCV routing looks like with the supercharger. You can see there really isn’t any difference. The PCV line is unchanged. The breather line is unchanged too, despite the fact that throttle body has moved. It goes from the same spot on the valve cover to the same spot on the throttle body. The only difference is that the breather line is still pre-supercharger while the PCV port is now post-supercharger.
The stock setup works because there's vacuum in the PCV line. If you pressurize the intake manifold with a supercharger, this goes away. At idle and probably under normal load, the system probably operates about the same because you’re not boosting much if at all. However, at wide open throttle there is boost which pressurizes the intake manifold. So, the PCV operation changes to this with a supercharger:
Why is this a problem? Basically, when running full out with forced induction, the PCV valve will close and won't be venting the crank case anymore.
What will happen? Well, I don’t really know for sure. I suspect what will happen is that because the breather tube doesn’t have any type of valve on it, the crank case will vent through the breather tube. So, instead of pressure and vapors going directly to your intake manifold, they’ll instead go through your throttle body, supercharger, and eventually reach the blower. Also, because no fresh air is coming in, you probably won’t do as effective a job at moving the bad vapors from the blowby out of the crankcase. However, some claim the crank case will build up pressure and start compromising the oil seals in the engine. I don’t see how this is possible. You may build up a little more pressure than normal, but you’re still venting pressure out the breather so it’s not like the engine will build pressure forever.
However, there is the possibility that the PCV valve fails open and you begin losing boost into the crank case. I suspect that if this happens you’ll probably start blowing a lot of oil out the breather tube and will start seeing something like this:
https://forum.ih8mud.com/threads/sc-and-oil-inhalation.911482/
So what is this mod all about?
https://forum.ih8mud.com/threads/pcv-101-for-forced-induction-80s.150299/
Basically, to do the mod, you route your PCV hose from the intake manifold to a port on the throttle body adapter. This puts your PCV hose pre-supercharger but post throttle body.
Essentially, this makes it exactly the same as the stock normally aspirated setup. You should always have vacuum on your PCV hose with this setup and it should work similar to stock form. The downside is that you’re now always venting through the supercharger. All the oil that typically builds up in the intake manifold will now be building up in your supercharger. To some extent this is probably already happening under boost for reasons I explained earlier, but with this mod it happens all the time. The advantage is that if your PCV fails open, there’s no chance of boosting the crank case and blowing out a lot of oil.
So is it recommended or not? In my opinion, both systems should work fine. If you keep on top of your PCV valve there’s really not much problem with the routing in the TRD instructions. I went into this research thinking I would do it, but after understanding the whole system, I don’t see much advantage. I’ll just make it more of a point than normal to pre-emptively replace my PCV valve.
One other point I’ll raise is that with the TRD recommended routing, a catch can on the breather hose might be beneficial if you really don’t want anything being vented through the rotors.
Anyway, hopefully this is a clearer explanation of what that mod is all about and what is going on with the PCV system when you supercharge. Hopefully I didn't make too many glaring errors.
Is there anyone that can ID any improvement between running the stock PVC setup versus this re-route thru the brake booster, on a TRD supercharged rig? There are times when I feel my rig with the original TArD setup goes kind of flat on performance once I get past 4500 rpm.