Catch Can Debate

[wootwoot]

"With a kit that blocks off the intake manifold port there's nothing actively drawing the gasses out of the crankcase."
I thought it was the blow-by from the crank case that actively pushed the gasses out of the crankcase? Are you saying this only happens during wide open throttle?

Tell me if I am understanding you:

The hose from the intake manifold to the crankcase is sucking pressure from the crankcase into the intake stream. This is where you think a catch can will be best placed.

The hose from the intake just before the throttle body to the crankcase is where the crankcase pulls air out of, or breaths from. It is essentially the air inlet to the crank case. This is where you suggest a breather would be best placed.

When you are cruising the engine is pulling air from one port and pushing it out the other, sending blow-by back into the intake stream via the intake manifold. When you are at wide open throttle (aka "fun time") the PCV on the line going from the block to the intake manifold closes and the crankcase vents air from the hose going from the block to the intake near the throttle body in order to relieve pressure. Is this correct?

If I have it correct this explains why ANTI_LAG was finding oil blow-by on both hoses and therefore thought that both hoses must be venting crank case pressure. If I understand you correctly, the hose from the block to the manifold relieves and recycles the blow-by during cruising but shuts during wide open throttle. The hose from the block to the intake feeds the crankcase fresh air during cruising but switches roles and vents crankcase pressure during wide open throttle.

If I understand you correctly it makes a lot of sense. It also explains why most people catch a lot of oil when they hook their catch can to the line from the block to the intake manifold and nearly none when when they connect them in the line from the intake to the block.

I suppose I could confirm that a catch can on the block-to-manifold line and a breather on the block-to-intake line would not cause a vacuum leak (as ANTI_LAG suggested) by simply unplugging the line to the intake and seeing what happened. If you are correct, it should run fine. If not, it should run rough and stall. My intuition is that it will not stall because that line, in my mind, is already vented to the atmosphere because the intake pipe opens up to the ambient air at the snorkel.

[Calum]

Originally Posted by wootwoot

"With a kit that blocks off the intake manifold port there's nothing actively drawing the gasses out of the crankcase."
I thought it was the blow-by from the crank case that actively pushed the gasses out of the crankcase? Are you saying this only happens during wide open throttle?

I suppose I could confirm that a catch can on the block-to-manifold line and a breather on the block-to-intake line would not cause a vacuum leak (as ANTI_LAG suggested) by simply unplugging the line to the intake and seeing what happened. If you are correct, it should run fine. If not, it should run rough and stall. My intuition is that it will not stall because that line, in my mind, is already vented to the atmosphere because the intake pipe opens up to the ambient air at the snorkel.

I agree with almost everything. Just, if you unplug the line to the intake, you'll want to plug the port just before the throttle body so you're not putting air, that the MAF hasn't measured, into the engine.

About the bolded section. Fluids flow due to a pressure differential, the greater the differential the greater the flow. The pressure differentials we're talking about in this system, unless something has gone drastically wrong, are in the plus or minus 10 psi range. In this tiny world though, that's a huge difference.

You are correct that pressure will build up in the crankcase and that pressure will push the gasses out even without the vacuum drawing the gasses out. But without the draw of the vacuum, the blowby gasses are experiencing half of the pressure differential and hence will flow half as fast. Also the blowby gasses are pushing on everything in the crankcase with the same pressure, including the oil at the bottom and the piston rings. With this in mind and the fact that the vast majority of driving is going to be effected by changing from the oem style system to the double breather, the blowby gasses will spend much more time in the crank case, will contaminate the oil much faster, and will inhibit ring sealing. This will further increase blowby, reducing efficiency, increase wear and compound the problem even farther.

Adding to that, a lot catch cans that I've seen use small tubing with convoluted routes. This will farther increase the pressure in the crankcase as now the pressure there will need to build up sufficiently to push the gasses through all of that.

If you're thinking that an extra few psi differential really wont make that much of a difference and that it couldn't be as catastrophic as I'm saying, you're partially correct. It would take a couple years of normal use to be able to measure the wear differences between the oem style and the open system or double breather.

[Sportsguy83]

Originally Posted by JoeBoxer

Yeah but it's $300 which although your weld quality is amazing i'm not paying that for a catch can especially since i'm NA anyways.

Well, that's right but you mentioned Crawford which is even more expensive than theirs so I can see why they felt left out...

[bakerr6]

I plan on buying the D3PE can, as it will work exactly as it should for the particular application I am looking to run. The only reason I haven't yet is because I'm not sure what turbo I'm going to run.

The conversation in here is on point, and really with a few variances, there are a couple other methods that would work also. I'm not going to get into any other variances, as really the method that Anti_lag is suggesting is the best method for most FI vehicles

[Sportsguy83]

Originally Posted by bakerr6

I plan on buying the D3PE can, as it will work exactly as it should for the particular application I am looking to run. The only reason I haven't yet is because I'm not sure what turbo I'm going to run.

The conversation in here is on point, and really with a few variances, there are a couple other methods that would work also. I'm not going to get into any other variances, as really the method that Anti_lag is suggesting is the best method for most FI vehicles

When you say "most" and not "all" FI vehicles, which examples can you give it where it would not work?

I am looking for a catch can too, just want to go with the one that best suites a FI street driven car.

[bakerr6]

That's a great question, it really depends on your setup. There are a few other caveats that would cause you to possibly change the routing, such as running a second power adder or meth injection. These shouldn't be a problem, but there could be a better way to run the catch can, especially if you must stay emmissions compliant.

meth and the second power adder should still work seamlessly with their setup, but if you are looking for a different way that I would set it up with running meth, lmk. I can send you a small drawing of what I plan on doing

[Sportsguy83]

Originally Posted by bakerr6

That's a great question, it really depends on your setup. There are a few other caveats that would cause you to possibly change the routing, such as running a second power adder or meth injection. These shouldn't be a problem, but there could be a better way to run the catch can, especially if you must stay emmissions compliant.

meth and the second power adder should still work seamlessly with their setup, but if you are looking for a different way that I would set it up with running meth, lmk. I can send you a small drawing of what I plan on doing

No emission tests in FL. Won't go with meth, I would rather go E85. I'm doing a turbo kit 320 whp max after future fuel upgrades. Street driven with rare track days.

[ANTI_LAG]

We run our style catch cans with meth inject, nitrous, etc. In a forced induction scenario there is not right way to do it but the way we have ours, unless you want to just dump the lines, but you'll risk oil downs at the track, oil residue over your engine, not being able to run at scca, road course, or drag strips.

[Sportsguy83]

Originally Posted by ANTI_LAG

We run our style catch cans with meth inject, nitrous, etc. In a forced induction scenario there is not right way to do it but the way we have ours, unless you want to just dump the lines, but you'll risk oil downs at the track, oil residue over your engine, not being able to run at scca, road course, or drag strips.

Sorry to keep bothering and probably being redundant, but are we absolutely sure the vacuum the intake makes is not necessary for proper PCV function? That is my only concern. I don't like dumping the blow-by to the ground and I don't need to pass any emission test so using the filters and dump to atmosphere is ok with me. I just want to understand it is a good solution and that not having the intake vacuum will not hurt the engine in any way.

The car will be FI when I install it.

[ANTI_LAG]

If your boosted then there will not be any vacuum under boost so the Oem style Pcv system will not function.

[ANTI_LAG]

I would also like to add as I said before, in the case where passing emissions is done by check of dtcs and readiness moniters, our catch can will pass. I'm not sure how California would work out as they are off thier rockers there. But we have emissions testing here in texas and it will pass.

[wootwoot]

Originally Posted by ANTI_LAG

If your boosted then there will not be any vacuum under boost so the Oem style Pcv system will not function.

Interesting. Never thought of that. So if you are running forced induction there is no vacuum under boost. Does that mean the PCV will ever shut? Or will it always stay open?

My next question is this: Where it the PCV valve? And how does it work? That is, what causes it to close/open?

We are doing good here guys. Keep it up.

[wootwoot]

Originally Posted by ANTI_LAG

I would also like to add as I said before, in the case where passing emissions is done by check of dtcs and readiness moniters, our catch can will pass. I'm not sure how California would work out as they are off thier rockers there. But we have emissions testing here in texas and it will pass.

Your can could possibly get the car impounded in CA. Depends on the mood of the cop that night. Nothing against the amazing quality of your can (function under debate at the moment). That's just the facts over here in my communist state. They are very stringent with emissions stuff. No cats could also do it. Illegal intake as well. They usually give fix-it tickets but sometimes things go real bad. There is a member on this forum that almost got his car taken due to having a breather tank when he was coming home from the track. Luckily he disconnected it before he left the track. Crazy...

I was planning on having everything in the car I needed to take the can off or disconnect it should I be pulled over. I would only need some pre-cut hose and maybe a pair of pliers. I think it would be a good bargaining chip if you ever got popped. Especially for driving too fast.

[Calum]

Originally Posted by wootwoot

Nothing against your amazing can.

I think this thread has taken a turn for the worse.