When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hi, adding a blower to a built 427 and would like to keep as much of the emissions crap as possible out of the intake and blower. I have had success in the past venting to atmosphere on boosted applications. I realize there would be no vacuum to pull out gasses, but at least my intake will remain clean. Even catch cans can and will put some gasses and residue into the intake if plumbed that way. I just prefer to not do that and vent to atmosphere. Below is the OEM setup and then a potential solution for me and would like to get the groups thoughts on if there would be any issues with the second image setup. It's basically eliminating the dirty side and then venting the oil tank vs plumbing back into the intake. I'm also considering running a hose to a bung welded in the exhaust in place of the breather filter on top of the catch can to help pull some air. Thanks for any and all feedback.
No, since without vacumn to the system when the motor is not on boost, going to cause the engine oil to get dirty really quick.
As for when on boost, going to be more blow by past the rings, to over pressure the PVC dry side lines if that is all that is in play.
So valley port stays in play with catch can, one way valve so boost is not lost out the intake port under presssure, and catch can get valved blow off filter so when the valley port is pushing lot of blow by pressure under boost, it has someone to go out of the catch can.
If you are not going to run the fuel rail covers, then can pull the blocker cap off the passenger rocker cover, to add in a vavle blow off filtered device there.
As for clean side, think Elite oil separate to replace the oil tank cap, which will keep the oil from reaching the intake, instead of using the catch can PVC port.
No, since without vacumn to the system when the motor is not on boost, going to cause the engine oil to get dirty really quick.
As for when on boost, going to be more blow by past the rings, to over pressure the PVC dry side lines if that is all that is in play.
So valley port stays in play with catch can, one way valve so boost is not lost out the intake port under presssure, and catch can get valved blow off filter so when the valley port is pushing lot of blow by pressure under boost, it has someone to go out of the catch can.
If you are not going to run the fuel rail covers, then can pull the blocker cap off the passenger rocker cover, to add in a vavle blow off filtered device there.
As for clean side, think Elite oil separate to replace the oil tank cap, which will keep the oil from reaching the intake, instead of using the catch can PVC port.
I do have another car that is vented to atmosphere and the oil life is fantastic. Looks almost new at 2500 miles, that's about when I change it since its non-synthetic. I'm not too worried about the lack of vacuum when not in boost, if I need to, I will change oil more often, but I think the oil will remain very clean just like my other car on 30psi.
When in boost, I'm hoping to keep blowby to a minimum as I won't be hitting too high of pressure, maybe 15psi, and I have gas ported rings to help with ring seal. That said, over pressurizing the valve cover lines is one of my concerns.
About the catch can at the valley cover, I tried that on the car with it NA. Still got oily residue into the intake. Even if a catch can keeps all of the oily residue out, there will still be gross gasses coming back into the intake, which is what I want to avoid. I would rather have a little higher crankcase pressure than nasty, incombustible gasses being pushed back into the intake.
I have vented my built LS7 to atmosphere for 10 years/52,000 miles. Change oil every 5,000 miles, use maybe 1/2 qt of oil between changes. Drains to a re-purposed plastic bottle, vent holes drilled in near the top, and with a screw on cap. What's not to like? Oh, btw, oil is not black or dirty at that interval. Thats why we have had oil filters for decades. I've had 10,000+rpm motorcycle engines that vented to atmosphere. Never had any issues with those, either........
I have vented my built LS7 to atmosphere for 10 years/52,000 miles. Change oil every 5,000 miles, use maybe 1/2 qt of oil between changes. Drains to a re-purposed plastic bottle, vent holes drilled in near the top, and with a screw on cap. What's not to like? Oh, btw, oil is not black or dirty at that interval. Thats why we have had oil filters for decades. I've had 10,000+rpm motorcycle engines that vented to atmosphere. Never had any issues with those, either........
Both valve covers merge together into one (Y fitting) larger line, then that line tees into the valley cover, with yet a larger line exiting last into the bottle. Sorry, no pics. With a blower, I do think you could benefit from some crankcase vacuum. This might be a great place for a header evac setup. Have you given any thought to adding some fittings to the collectors? Then run some combination lines to the valve and valley covers. I urge you to use valve covers with some sort of baffling. This setup would give maximum vacuum at WOT, where you'll need it most. However, if youre running cats, you'll have to hook this setup up after the cats, or you'll probably plug them fairly quickly. Hope this helps........
Both valve covers merge together into one (Y fitting) larger line, then that line tees into the valley cover, with yet a larger line exiting last into the bottle. Sorry, no pics. With a blower, I do think you could benefit from some crankcase vacuum. This might be a great place for a header evac setup. Have you given any thought to adding some fittings to the collectors? Then run some combination lines to the valve and valley covers. I urge you to use valve covers with some sort of baffling. This setup would give maximum vacuum at WOT, where you'll need it most. However, if youre running cats, you'll have to hook this setup up after the cats, or you'll probably plug them fairly quickly. Hope this helps........
So if I'm understanding correctly, you have nothing going to the dry sump tank? Both ports capped on it?
I've thought about the exhaust yes, or just a hose unning along the bottom of the car so as im driving i get the same effect from air moving under the car.
No problems with oil all over the engine bay? Other engines I've had open venting on had to get oil wiped up after race day or burning oil smell from it getting on exhaust.
No problems with oil all over the engine bay? Other engines I've had open venting on had to get oil wiped up after race day or burning oil smell from it getting on exhaust.
Sounds like your catch cans weren't doing much. In my experience, I have a vented can with a hose (in place of the breather filter) run under the car to almost the back axle. 30psi of boost, no smell, no mess. But also a good can so I'm not sure what to tell you.
Last edited by mgrotel; Feb 7, 2024 at 01:15 PM.
Reason: added additional comments
No problems with oil all over the engine bay? Other engines I've had open venting on had to get oil wiped up after race day or burning oil smell from it getting on exhaust.
But the short answer to your question is no problem at all, id rather it be on the outside than tossing that garbage back into my intake asking for detonation.
So if I'm understanding correctly, you have nothing going to the dry sump tank? Both ports capped on it?
I've thought about the exhaust yes, or just a hose unning along the bottom of the car so as im driving i get the same effect from air moving under the car.
No cats, oem valve covers with good baffling.
I have a wet sump LS7 in a C5. However, you can vent to atmosphere in any setup. I have no issues with spilled oil, smell, or smoke. But you have to keep an eye on the oil level in the bottle. How often depends on bottle size and engine usage. Any PCV system, catch can or not, will eventually have intake contamination. There's no way around it. Sure, a catch can helps. But it doesn't eliminate, or treat the cause, which is pretty simple, really. When you hook a vacuum pump up to an oil mist, said vacuum pump can, and will, eventually suck enough mist into the intake to create residual oil in the intake. The LS7s have enough problems as is, and sure don't need to add oil puddles in the intake manifold to the list.
Just ordered an Earl's baffled valve cover cap for a little extra venting that I'll plumb to the catch can too.
I check my oil almost every time I drive it.
You'll find that checking the oil every time you drive is not necessary, unless you're sucking large quantities of it into the manifold and into the combustion chambers. Or if you're leaking it badly. I check mine every month or two. It is always at, or very near, full.
Crankcase pressure always reduce ring function and forces oil into piston rings and combustion chamber bypassing the intake route completely. Improper piston drainage leads to hard carbon deposits and ruins cylinder wall.
Crankcase pressure directly controls oil droplet density and radius. More pressure results with larger droplets and more oil suspension.
The more vacuum pulled on crankcase the better rings will function, better pistons drain oil, cleaner oil circulating reduce carbon deposits around orifices, and reduce oil suspension in crankcase gas allowing more crankcase scavenging with less oil contamination to the intake.
Never vent to atmosphere.
Originally Posted by TurboLX
Lots of people are also wrong about PCV needs with sustained boost. Follow the steps above to properly evacuate the crankcase using either manifold vacuum or compressor inlet depression at all times. Oil is roughly 48 Octane, so it only takes a little bit of it to dope down your average regardless of what fuel is in the tank.
Originally Posted by TurboLX
If you are building crankcase pressure (from blowby on the power stroke without proper evacuation), this pressure can also go the other way past the rings during the intake stroke. You can get oil ingestion to the cylinder past the rings without ever going trough the traditional PCV route (intake system). Even if this isn't 100% of your current knock source, it must be addressed.Venting to atmosphere is Busch league ****, do it right.
Crankcase pressure always reduce ring function and forces oil into piston rings and combustion chamber bypassing the intake route completely. Improper piston drainage leads to hard carbon deposits and ruins cylinder wall.
Crankcase pressure directly controls oil droplet density and radius. More pressure results with larger droplets and more oil suspension.
The more vacuum pulled on crankcase the better rings will function, better pistons drain oil, cleaner oil circulating reduce carbon deposits around orifices, and reduce oil suspension in crankcase gas allowing more crankcase scavenging with less oil contamination to the intake.
Thoughts on this LS7 crankcase venting solution
