Another Catch Can Thread
11-16-2011, 07:09 PM
#1
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Another Catch Can Thread
After browsing around about catch can, I decided to put one together. I am not FI'd yet, so this is just using a "compressor/air filter" from lowes and two silicone hoses. Anyways, so I used a T fitting to connect the passenger and driver side together and then run that into the catch can. Is that legit? I noticed everyone runs two lines into the catch can, rather than joining them. Why is that? From what I can tell, they both seem to be exit ports right? or is the passenger side dual purpose in that case?
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11-16-2011, 08:11 PM
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Especially for NA, I believe the standard is the stronger 323 PCV valve and an otherwise stock system. Street FI can put a check valve between the inlet manifold and valve cover to prevent the boost from damaging the PCV valve, and causing leakage, therefore pressurizing the head.
Tracked FI cars generally require larger (-6 or -8) lines from both sides of the valve cover going into a catch can that may or may not drain back into block via the stock drain port.
All of these have known to fail in either of these situations, search for "catch can" and you'll get a couple dozen unanswered threads, yet each have dozens of replies.
Tracked FI cars generally require larger (-6 or -8) lines from both sides of the valve cover going into a catch can that may or may not drain back into block via the stock drain port.
All of these have known to fail in either of these situations, search for "catch can" and you'll get a couple dozen unanswered threads, yet each have dozens of replies.
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11-16-2011, 08:22 PM
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I am not even running a PCV valve. just straight out, into the T and then that into the can + filter and VTA.
What do you mean by failure btw?
I just get the feeling from reading around, that its probably a good idea to keep vacuum on the crankcase when Naturally aspirated. or am I mistaken here?
What do you mean by failure btw?
I just get the feeling from reading around, that its probably a good idea to keep vacuum on the crankcase when Naturally aspirated. or am I mistaken here?
Last edited by Seefo; 11-16-2011 at 08:42 PM.
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11-16-2011, 09:22 PM
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Further reading on topic, It seems that for N/A track car (which is what I am for now), it would be best to run the catch can off the breather and keep the PCV (under street driving and low throttle, I would keep the benefit of vacuum helping evacuate stuff. Under high throttle all the gases would be out into the catch can and VTA).
Or perhaps, I can just hook up the PCV port (with no PCV) into the catch can during track events for more breathing.
Someone tell me if I am silly or not.
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11-16-2011, 10:43 PM
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Here is the way I am seeing PCV under vacuum:
Advantages:
-Helps with low throttle/cruise evacuation
Disadvantages:
-less evacuation porting under heavy throttle, where the PCV will close and the breather does all the work.
-The crankcase gases under low throttle/cruise are much less than under heavy throttle/track use. So we are effectively giving up some when it matters most, to gain some when its not as important...
I just question the logic behind it, as PCV wouldn't be used if it wasn't without merit. At least in naturally aspirated applications.
At this point, I think I am going to run without PCV this weekend (RA, full/high throttle time is probably the most out of any event I can drive to), but keep two catch cans. just so I can see how much I collect from each hole. Then run a week in the same configuration, but daily driving and see which side collects more. Then one more week with the PCV under vacuum and compare a third set. I think that would be a good measure of what is working under which conditions...Unless someone can shoot a hole in this "theorizing"
Advantages:
-Helps with low throttle/cruise evacuation
Disadvantages:
-less evacuation porting under heavy throttle, where the PCV will close and the breather does all the work.
-The crankcase gases under low throttle/cruise are much less than under heavy throttle/track use. So we are effectively giving up some when it matters most, to gain some when its not as important...
I just question the logic behind it, as PCV wouldn't be used if it wasn't without merit. At least in naturally aspirated applications.
At this point, I think I am going to run without PCV this weekend (RA, full/high throttle time is probably the most out of any event I can drive to), but keep two catch cans. just so I can see how much I collect from each hole. Then run a week in the same configuration, but daily driving and see which side collects more. Then one more week with the PCV under vacuum and compare a third set. I think that would be a good measure of what is working under which conditions...Unless someone can shoot a hole in this "theorizing"
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11-17-2011, 01:43 AM
#8
I may be wrong, but I thought that the PCV system still evacuated the crankcase even under high load due to the air rushing through the intake and past the PCV port creating a low pressure area relative to the crank case (even though the engine is not "pulling vacuum" per say). You still have a mass of air and it's moving fastest at WOT.
As for the vent system itself: I've read some engineering papers on the subject (best I can offer not being an engineer or being on a baller *** racing team to really test this) and they suggest that a vacuum on the crank case pulls rings toward the cylinder walls and helps with sealing as well as prevents pressure build up that can lead to premature seal failure (like front/rear mains, oil pan,etc). Certainly if you open any issue of Car craft, or some such publication, they'll show you a big block v8 that gained 20whp from a $500 vacuum pump they ordered off jegs.
From my experience in rx7 land I can tell you this. Turbos create more blowby and thus contaminate the engine oil quicker (especially apparent in rotaries). As such its considered acceptable to run them with no PCV and a catch can vented to atmosphere, because the extra pressure on the crank case will evacuate it anyway.
What people have learned on the track is, you need both sides vented otherwise, if you turn away from your vent, the pressure has no where to go, and you fill your catch can with oil. I know of some RX-7 guys that couldn't go longer than a session before their catch can was overflowing, adding another vent on the passenger side of the engine totally eliminated this.
What you can be sure of is this: you definitely want the left and right side of your engine vented. And even though it's not entirely necessary, you should WANT vacuum on your crankcase. you NEED at least an atmospheric vent. For vacuum, you either need an intake PCV system, or an exhaust scavenge system. If you don't get your vehicles emission tested, the exhaust system is clearly superior. Otherwise, just run it through the intake and deal with a slightly dirtier intake manifold.
Your choice, the environment or your internals? For my play vehicles I go the exhaust route.
As for the vent system itself: I've read some engineering papers on the subject (best I can offer not being an engineer or being on a baller *** racing team to really test this) and they suggest that a vacuum on the crank case pulls rings toward the cylinder walls and helps with sealing as well as prevents pressure build up that can lead to premature seal failure (like front/rear mains, oil pan,etc). Certainly if you open any issue of Car craft, or some such publication, they'll show you a big block v8 that gained 20whp from a $500 vacuum pump they ordered off jegs.
From my experience in rx7 land I can tell you this. Turbos create more blowby and thus contaminate the engine oil quicker (especially apparent in rotaries). As such its considered acceptable to run them with no PCV and a catch can vented to atmosphere, because the extra pressure on the crank case will evacuate it anyway.
What people have learned on the track is, you need both sides vented otherwise, if you turn away from your vent, the pressure has no where to go, and you fill your catch can with oil. I know of some RX-7 guys that couldn't go longer than a session before their catch can was overflowing, adding another vent on the passenger side of the engine totally eliminated this.
What you can be sure of is this: you definitely want the left and right side of your engine vented. And even though it's not entirely necessary, you should WANT vacuum on your crankcase. you NEED at least an atmospheric vent. For vacuum, you either need an intake PCV system, or an exhaust scavenge system. If you don't get your vehicles emission tested, the exhaust system is clearly superior. Otherwise, just run it through the intake and deal with a slightly dirtier intake manifold.
Your choice, the environment or your internals? For my play vehicles I go the exhaust route.
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11-17-2011, 03:29 AM
#9
Is it wrong to connect the pcv valve as per normal with lets say an "perfect" one way valve. Vacuum in cruise/closed under boost. The driver side to the turbo intake through a catch can. IE; vavle cover to catchcan to intake? Or completely remove the PCV crap, hook both lines to the catch can, then to intake. Keep the crank case under some vacuum. Not fill intake with oil via a catchcan. The later is my plan. Been reading a lot about these systems and the later senario makes the eco ***** scream but not try to hang you as much as the exhaust vent route. Plus the exhaust route isn't really street car/easy/the direction I'd want. The strait vent to atmo cans don't provide any vacuum and no catchcan runs the "hey my intake is full of oil" conversation.
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11-17-2011, 07:37 AM
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^well for you, I think you have to consider the amount of boost. Eventually too much boost and you could end up pushing air the other way (from the intake into the crankcase through the PCV), and thats not good from what I have been reading on here. in your case you have pressure in the intake manifold and pressure in the crank case. Since pressure goes from high to low, the intake manifold pressure will want to move to the crankcase. Thats why some guys move to the 323 GTX PCV, which is stronger and can take more boost.
I don't think the PCV is open at high throttle/low vacuum. At least, everything I have read indicates that it shouldn't be open if the breather is doing its job. As for the vacuum and all that, yea I totally agree vacuum is good, and yes there is plenty of drag cars that run a vacuum pumps to help with ring sealing and get power out of it. but at the same time, those cars are N/A, running ridiculous amounts of displacement, power and compression, so their blowby is plenty high, and they are still running VTA (vacuum pump to catch can to a filter to VTA).
Plus, there is a few things different here: First at high throttle there is little if any vacuum in the intake, so technically you are not gaining any vacuum benefits during that period of time. Those vacuum pump drag cars still are, since the vacuum pump works regardless. So they don't have anything to worry about, other than making sure the pump can evacuate more crankcase gas than the pistons can create (otherwise they would be pressurizing the crank case). I will look into the exhaust route, but the issue is that I wanted to setup a catch can now that way when I went FI'd I would already be prepared. Too bad it had to be this complicated lol. Has anyone ran a vacuum pump on a miata?
I don't think the PCV is open at high throttle/low vacuum. At least, everything I have read indicates that it shouldn't be open if the breather is doing its job. As for the vacuum and all that, yea I totally agree vacuum is good, and yes there is plenty of drag cars that run a vacuum pumps to help with ring sealing and get power out of it. but at the same time, those cars are N/A, running ridiculous amounts of displacement, power and compression, so their blowby is plenty high, and they are still running VTA (vacuum pump to catch can to a filter to VTA).
Plus, there is a few things different here: First at high throttle there is little if any vacuum in the intake, so technically you are not gaining any vacuum benefits during that period of time. Those vacuum pump drag cars still are, since the vacuum pump works regardless. So they don't have anything to worry about, other than making sure the pump can evacuate more crankcase gas than the pistons can create (otherwise they would be pressurizing the crank case). I will look into the exhaust route, but the issue is that I wanted to setup a catch can now that way when I went FI'd I would already be prepared. Too bad it had to be this complicated lol. Has anyone ran a vacuum pump on a miata?
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11-17-2011, 08:40 PM
#11
Running a pump is useful on a NA car. How ever can be expensive and bulky. However one thing you could do now is run a check valve to the exhaust, install it at an angle in the exhaust system. The exhaust will create a vacuum thus assisting in the evacuation of crank case pressure. We installed this same system on a Twin Turbo SRT-10 Truck we built, and it worked flawlessly.
This is a great option if you are NA or turbo.
We tend to use catch cans or Tanks on our personal and customers cars. Your main goal here is to release the crank case of the pressure buildup under load. Helping the rings to seal and help create more power.
Here is a link to a universal kit for Exhaust evacuation system.
Clicky here!
This is a great option if you are NA or turbo.
We tend to use catch cans or Tanks on our personal and customers cars. Your main goal here is to release the crank case of the pressure buildup under load. Helping the rings to seal and help create more power.
Here is a link to a universal kit for Exhaust evacuation system.
Clicky here!
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11-23-2011, 09:14 AM
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I appreciate that Savington. I ran the catch can on the breather for the RA weekend...and not a single drop in it. I will update as I change the setup for dec. 3-4 at RA also. I think I will put both PCV and driver side to a catch can and then keep it under vacuum, just for ***** and giggles.
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