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Can anyone weigh in on crank case pressure at high RPM?
I have a 427 LS, btr stage 3 NA ls7 cam and a Holley midrise single plane intake with a Wilson manifolds 4150 TB.
my current crank case vent setup is this :
each valve cover has a -10an bulkhead attached to the to rear. From there, they run -10 hose to a catch can that has a breather on top.
I’m at high rpm, I get a lot of oil that leaks from the passenger side VC and the oil cap (they are proform covers and the oil cap is a push it style, doesn’t seal very well.
this is causing a lot of oil to burn off as well as make a mess.
I know that excess crank case pressure will cause seals to blow out etc but I’d imagine with both valve covers opened up it shouldn’t be an issue.
a friend of mine that owns a shop and builds some pretty badass race cars (he’s got a 2000hp pro stock Camaro with a blown 509ci on e85)
told me that if it’s vented and still blowing out oil that I probably need to seal the valve covers and run a pcv valve to the throttle body for vacuum.
M/E Wagner makes a pretty trick pcv valve that’s adjustable depending on your engine’s vacuum characteristics..
I have also dug online and found that if the crank case pressure is higher than the pressure blown by the rings during combustion, it’ll actually limit how much the engine can rev/power it’ll make etc.
this seems interesting because my engine seems to make peak at 6k.
a friend of mine that owns a shop and builds some pretty badass race cars (he’s got a 2000hp pro stock Camaro with a blown 509ci on e85)
told me that if it’s vented and still blowing out oil that I probably need to seal the valve covers and run a pcv valve to the throttle body for vacuum.
The problem is that the PCV relies on vacuum and you'll only have vacuum at idle/part throttle not so much at WOT when blowby is at it's highest. I would look at getting the valve covers to seal properly so all excess pressure in vented into the catch can(s) Another option is to run a vacuum pump.
If it's NA, you need a PCV system unless you have a vacuum pump. It doesn't matter if it's a 700hp LS or 200hp 350 Chevy, it needs it. Have seen the same mistake over and over. Just run a pcv w/ a good catch can set-up and it'll solve a lot of problems.
If it's NA, you need a PCV system unless you have a vacuum pump. It doesn't matter if it's a 700hp LS or 200hp 350 Chevy, it needs it. Have seen the same mistake over and over. Just run a pcv w/ a good catch can set-up and it'll solve a lot of problems.
will any old pcv work or should I look into an adjustable one? M/E Wagner makes an adjustable one that you can fine tune for your engines specific vac at idle and cruising
will any old pcv work or should I look into an adjustable one? M/E Wagner makes an adjustable one that you can fine tune for your engines specific vac at idle and cruising
More adjustability is always better, but a standard system w/ something like a Mighty Mouse catch can is really all you need. Your combo is not crazy way out there, lots of guys running exactly the same set-up w/ no issues. Now if you put a pcv system in and still have a problem, then you need to look at the ring seal.
Also, you can't have any faith in China **** proform parts. There may be a problem there, also. One step at a time. FYI, whatever catch system you run, follow their instructions on the system is run/sealed w/o any "great ideas", at least on the first install. Run it how they tell you and do testing, then report back.
If it's NA, you need a PCV system unless you have a vacuum pump. It doesn't matter if it's a 700hp LS or 200hp 350 Chevy, it needs it. Have seen the same mistake over and over. Just run a pcv w/ a good catch can set-up and it'll solve a lot of problems.
PCV systems work well for emissions and helping keep the engine clean but they do next to nothing under load where crankcase pressure is highest. How will it help in his situation?
I run a catch can and then a #10 line from the valve cover to the intake accordian thing with another catch can in between the valve cover to accordian thing as a filter. The OEM PCV only has a .100 inch restrictor hole and that is all you need for a PCV. The PCV only flows 2 cfm (with 15 inches of vacuum) at best so you need another breather as a 700 hp motor at WOT will throw off 20 cfm of bad air in the crankcase. If you run a straight 3/8 unrestricted hose/orifice to the PCV you will fill the intake with oil as a 3/8 hole at 15+ inches of vacuum flows like 20 cfm and will suck the oil out from the valley pan / valve cover into your manifold - it needs a restrictor. The older cars had a pintal valve as a restrictor. You will notice the GZ vacuum pumps are like 22 cfm for 700-800 hp. Here is a photo of the restrictor in your valley pan and or valve cover it is only .100 and it is designed that way. So the other 18-20 cfm needs to go out the valve cover just like the old car except now it is recycled into your accordian thing in the intake tract. This is an older photo where I used the dry sump tank as a catch can for the 18-20 cfm and I had a catch can in the front for the PCV specific (2 cfm). Basically I had two 3/8 lines going to dry sump tank and then a #8 to accordian thing. Two separate issues/paths here PCV (under 10% at WOT) and the 90+% of the rest of the blow off at WOT. The sole purpose of PCV is to get the bad air out of the motor most of the time with a breather vent system that kicks in at more throttle.
I run a catch can and then a #10 line from the valve cover to the intake accordian thing with another catch can in between the valve cover to accordian thing as a filter. The OEM PCV only has a .100 inch restrictor hole and that is all you need for a PCV. The PCV only flows 2 cfm (with 15 inches of vacuum) at best so you need another breather as a 700 hp motor at WOT will throw off 20 cfm of bad air in the crankcase. If you run a straight 3/8 unrestricted hose/orifice to the PCV you will fill the intake with oil as a 3/8 hole at 15+ inches of vacuum flows like 20 cfm and will suck the oil out from the valley pan / valve cover into your manifold - it needs a restrictor. The older cars had a pintal valve as a restrictor. You will notice the GZ vacuum pumps are like 22 cfm for 700-800 hp. Here is a photo of the restrictor in your valley pan and or valve cover it is only .100 and it is designed that way. So the other 18-20 cfm needs to go out the valve cover just like the old car except now it is recycled into your accordian thing in the intake tract. This is an older photo where I used the dry sump tank as a catch can for the 18-20 cfm and I had a catch can in the front for the PCV specific (2 cfm). Basically I had two 3/8 lines going to dry sump tank and then a #8 to accordian thing. Two separate issues/paths here PCV (under 10% at WOT) and the 90+% of the rest of the blow off at WOT. The sole purpose of PCV is to get the bad air out of the motor most of the time with a breather vent system that kicks in at more throttle.
This is what I understand from this.
I can run a 3/8” hose from my driver side VC because it’s got a restricted orifice tube in it to the intake manifold for vacuum for pcv.
then I can keep a -10 an hose that would go from my passenger VC to the catch can that is vented to atmosphere through a breather? Or do I need to run a -10 from the catch can to the intake pre TB?
If it's NA, you need a PCV system unless you have a vacuum pump. It doesn't matter if it's a 700hp LS or 200hp 350 Chevy, it needs it. Have seen the same mistake over and over. Just run a pcv w/ a good catch can set-up and it'll solve a lot of problems.
I have vented many, many N/A engines to atmosphere without issue. No excessive oil collection in cans, ever (there’s always going to be a little oil in the bottom of the can, no matter what), and no mess. My 434 in my Chevelle is the same way. I avoid PCV setups unless it’s necessary for emissions, whenever possible. I don’t see the need from a performance standpoint, to allow the oil mist to re-enter the intake, if it’s avoidable. I’ve found that these LS engines make more crankcase windage than the previous SBC’s, and in my opinion, anything we can do to keep this out of the intake is a good thing…again speaking from a performance standpoint only. I don’t think that’s the issue here. Judging by the numbers in the other thread, and what’s going on here, I’d say there a ring seal issue or something similar. Almost sounds like the engine has way too much oil in it, but that would not cost 100ish hp.
PCV systems work well for emissions and helping keep the engine clean but they do next to nothing under load where crankcase pressure is highest. How will it help in his situation?
in theory, you are right, but having a pcv allows for some vacuum and transition from pressurized to non-pressurized crankcase environment. It's not an absolute like the theory suggests. Reality is, the engine will spend majority of time at part throttled. I have seen waaayyy more problems from no pcv than with, by far. A lot of people make the same "it screws up the mixture/tuning argument", but I have yet to see proof of that in action. I think the crankcase pressure screws up the tune more.
I have vented many, many N/A engines to atmosphere without issue. No excessive oil collection in cans, ever (there’s always going to be a little oil in the bottom of the can, no matter what), and no mess. My 434 in my Chevelle is the same way. I avoid PCV setups unless it’s necessary for emissions, whenever possible. I don’t see the need from a performance standpoint, to allow the oil mist to re-enter the intake, if it’s avoidable. I’ve found that these LS engines make more crankcase windage than the previous SBC’s, and in my opinion, anything we can do to keep this out of the intake is a good thing…again speaking from a performance standpoint only. I don’t think that’s the issue here. Judging by the numbers in the other thread, and what’s going on here, I’d say there a ring seal issue or something similar. Almost sounds like the engine has way too much oil in it, but that would not cost 100ish hp.
i don't disagree with you, but I think your circle track experience definitely helps whatever system you are running. Also, I know your machine work on your own motors is top notch, which certainly helps tremendously. I have worked on so much questionable stuff from other people, and higher mileage stuff that the pcv just works in 99% of the cases.
Yes run the 3/8 hose from restricted orifice valve cover to the intake via the catch can. You can then run a #10 from the valve cover to the breather can or if you want to keep it enviromentally friendly run it to the accordian thing. I run it with another catch can to keep the oil mist out of the accordian thing as best as possible. Like I said the PCV does not help at WOT (or even 1/2 WOT) so you might as others have said have other issues going on in the engine.
i have a NA lsx454 687rwhp and Mine was doing the same at one stage when i didnt have the pcv system routed correctly.
My setup now is -10an hose from cold air intake to your drivers side valve cover (clean air in)
-16an hose from oil fill to catch can, out of can thru pcv on can to intake manifold. on top of the can i have a one way breather which i think is the key to everything working properly.
When cruising it runs as a closed pcv system, drawing vacuum. Clean air in one valve cover, dirty air out thru oil fill thru catch can then to intake manifold
At wot the one way breather valve opens venting to atmosphere.
You need a clean air in and a dirty air out, smaller pipe ffor clean air , larger for dirty air out, the dirty air will always go least path of resistance.
Stuff your catch can with stainless steel wool to seperate oil from air
i have a NA lsx454 687rwhp and Mine was doing the same at one stage when i didnt have the pcv system routed correctly.
My setup now is -10an hose from cold air intake to your drivers side valve cover (clean air in)
-16an hose from oil fill to catch can, out of can thru pcv on can to intake manifold. on top of the can i have a one way breather which i think is the key to everything working properly.
When cruising it runs as a closed pcv system, drawing vacuum. Clean air in one valve cover, dirty air out thru oil fill thru catch can then to intake manifold
At wot the one way breather valve opens venting to atmosphere.
You need a clean air in and a dirty air out, smaller pipe ffor clean air , larger for dirty air out, the dirty air will always go least path of resistance.
Stuff your catch can with stainless steel wool to seperate oil from air
this is what i have but american driver side valve cover going to throttle body
this is what i have but american driver side valve cover going to throttle body
And your not happy with how it works? The vacuum pump is worth a few ponies.
Im happy with how mine works, 1/2 inch of oil in bottom of can every month. No oil whatsoever in intake manifold. If for whatever reason i start my car i make sure i get it up to temp, that way i evaporate all the water so none ends up in the can... Did think about getting the gz pump, was just unsure how reliable they are seeing tho i daily my car. Once i see that cars with them on are getting 30-40k out of them, ill get one, until then ill stay with what i have
That seems pretty high at 17%. You may be in the early stages of the rings going. Also it is not all about ring seal either. The second piston ring is also used for oil control can be giving way and allowing for oil to pass by into the intake manifold. Then you just said the word nitrous and what are the details here? Take a look inside the manifold and see if it has a lot of oil in it. Given it is a single plane intake you might not see much or take a peak inside the intake ports. With us guys with low rise plastic intakes the oil can puddle in the bottom of them which will not be the case here.
03-26-2022, 11:41 AM
Can anyone weigh in on crank case pressure at high RPM? 
