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I posted this in my build thread, but figured I'd stick it here too because it's relevant.
THE CAR:
The car in question (mine) is a stock 1.6L motor with MKTurbo setup, no boost control, MSPNP2. Last engine compression test was 3 months ago, 180 psi on all cylinders. I've done extensive boost leak testing, and mitigated all boost leaks except for the PCV setup.
THE DATA:
All of the lines below are 4th gear WOT pulls. X axis is RPM, Y axis is MAP PSI.
THE RESULTS:
- Yellow line is OEM PCV valve. Blue line is GTX PCV valve. Both runs were with the PCV hooked up to the IM. In this test, they performed identically. In both cases, I can hear boost leaking out of the driver side crankcase vent when I'm at WOT.
- When I disconnected the PCV valve entirely (orange line) and capped the IM, spool actually got worse- but only because the boost leak was gone, and it was sending a stronger boost signal to the wastegate actuator, which is activating the actuator sooner. I no longer hear the hissing boost leak.
- When I increased the actuator preload (grey), spool got much better.
THE CONCLUSIONS:
- Brain is right, the GTX valve is a $25 paperweight.
- Sixshooter is also right, All PCV valves leak boost without a check valve in line. At least the ones that I've tested- OEM, two different ones from NAPA, one from Autozone, and the GTX valve.
- Capping the IM and running both crankcase vents to atmosphere appears to be the best way to get fast, predictable spool and stable idle. In my case, it's narrowed things down to a single variable (wastegate preload).
As an interesting sidenote: all of the plots start to break up above 4000 rpm. I'm speculating that this is where the airflow becomes less laminar and more turbulent. This may be where you would see an improvement from better flowing manifold and/or head.
Last edited by Schroedinger; 10-30-2017 at 03:11 PM.
I posted this in my build thread, but figured I'd stick it here too because it's relevant. All of the lines below are 4th gear WOT pulls.
The car in question (mine) is a stock 1.6L motor with MKTurbo setup, no boost control, MSPNP2.
- Yellow line is OEM PCV valve. Blue line is GTX PCV valve. Both runs were with the PCV hooked up to the IM. In this test, they performed identically.
- When I disconnected the PCV valve entirely (orange line) and capped the IM, spool actually got worse- but only because the boost leak was gone, and it was sending a stronger boost signal to the wastegate actuator.
- When I increased the actuator preload (grey), spool got much better.
CONCLUSIONS:
- Brain is right, the GTX valve is a $25 paperweight.
- Sixshooter is also right, All PCV valves leak boost without a check valve in line.
- Capping the IM and running both vents to atmosphere appears to be the best way to get fast, predictable spool.
..and prevent blowby in an engine with tired rings?
THE RESULTS:
1. - Yellow line is OEM PCV valve. Blue line is GTX PCV valve. Both runs were with the PCV hooked up to the IM. In this test, they performed identically. In both cases, I can hear boost leaking out of the driver side crankcase vent when I'm at WOT.
2. - When I disconnected the PCV valve entirely (orange line) and capped the IM, spool actually got worse- but only because the boost leak was gone, and it was sending a stronger boost signal to the wastegate actuator, which is activating the actuator sooner. I no longer hear the hissing boost leak.
3. - When I increased the actuator preload (grey), spool got much better.
Brain- I agree with you in the linear regions. This leads us to a theory that I'd like to prove or disprove:
The stock PCV system leaks boost. It's a slow enough leak that the direct affect on the air entering the motor, which is constrained by flow and volumetric efficiency, is minor. The direct affect on wastegate actuation, which involves only pressure and not airflow, is profound.
I'm going to do a run with current (higher) wastegate preload, and connect the PCV valve back to the manifold. Which PCV valve shouldn't matter, but I'll use the GTX one. If this theory holds, the result should be very much like the grey plot. Will try to do this tomorrow.
Last edited by Schroedinger; 10-30-2017 at 04:01 PM.
Brain- I agree with you in the linear regions. This leads us to a theory that I'd like to prove or disprove:
The stock PCV system leaks boost. It's a slow enough leak that the direct affect on the air entering the motor, which is constrained by flow and volumetric efficiency, is minor. The direct affect on wastegate actuation, which involves only pressure and not airflow, is profound.
I'm going to do a run with current (higher) wastegate preload, and connect the PCV valve back to the manifold. Which PCV valve shouldn't matter, but I'll use the GTX one. If this theory holds, the result should be very much like the grey plot. Will try to do this tomorrow.
If it ends up like the grey plot the only thing you've proven is the preload has the profound effect while the PCV or not has negligible effect on boost attainment.
^ the only difference between the blue/yellow plots and the orange plot was whether the PCV was hooked up to the intake manifold. So it's clear that the PCV makes a profound difference to spool, although not in the manner that I expected.
The fact that the lines above all coincide in the linear region, before the wastegate opens, whether or not the boost was leaking through the PCV, would suggest that the boost leak is a small contributor to the dynamic flow of air entering the motor (at least at low RPM/boost levels). If true, this would lead us to the conclusion that PCV systems may still be a problem for aftermarket turbo setups, but not for the reasons we thought.
Thoughts up until now.
- PCV valves leak boost. Seems like they all leak about the same.
- In my simply managed turbo system, the leak has a profound affect on spool, for reasons that are unclear.
- We don't know whether that's because of less boost entering the engine (dynamic), or less boost hitting the wastegate actuator (static).
- The spool graph shows two regions: before the WG opens, and after.
- before the WG opens, the leak doesn't seem to affect spool much. This may or may not be true at higher RPM and/or boost levels, when the motor is operating at higher VE.
- the leak seems to matter a lot as far as when the WG opens, and what happens after it opens.
- my two variables are 1) PCV boost leaks and 2) WG actuator pre-load. These variables may not be independent; perhaps higher wastegate preload mitigates the affects of the PCV boost leak.
Last edited by Schroedinger; 10-30-2017 at 04:59 PM.
Sorry to derail again.
When I did a leak down, I had most of the Air coming out the dipstick tube. Meaning I have crappy rings. In addition, I smoke a decent amount under boost. Less so since I changed out an old UEGO sensor, but it’s definitely still smoking.
Im running a GTX PCV valve to a catch can, to the intake manifold. It’s an eBay baffled can (was like 50$, some funny brand name) full of copper wool, 3/8 rubber hose.
I’ll do a couple boost runs, look for smoke. Then cap off the IM, block off the outlet on the catch can and add a breather to it instead.
Sorry to derail again.
When I did a leak down, I had most of the Air coming out the dipstick tube. Meaning I have crappy rings. In addition, I smoke a decent amount under boost. Less so since I changed out an old UEGO sensor, but it’s definitely still smoking.
Im running a GTX PCV valve to a catch can, to the valve cover. It’s an eBay baffled can (was like 50$, some funny brand name) full of copper wool, 3/8 rubber hose.
I’ll do a couple boost runs, look for smoke. Then cap off the IM, block off the outlet on the catch can and add a breather to it instead.
I need pics of this.
Also: If you don't have your IM attached to your PCV, then you need to not have the PCV in there.
IATs need to be compared between the plots or we might be inadvertently measuring the wrong variable.
I have that data in the logs. I expect that there will be significant differences between the runs. Let me noodle on how to figure out whether or not it matters; may be able to just do a statistical correlation.
As one observation, I'm pretty sure there was a big difference in ambient temperature between the run with the OEM valve and the GTX valve, yet the plots are identical.
May be easier to start fresh- consider everything above to be the pilot study. If I have time tomorrow morning, I'll try two consecutive runs with the current wastegate preload.
- GTX PCV valve, connected to IM.
- no PCV valve, IM plugged; crankcase VTA on both sides.
Thinking this through further. I’m going to get my WG optimized first (max spool without boost creep), then test different PCV options while keeping wastegate the same. Best way to remove it as a variable.
why not just run both IM lines to a single catch can? The easy thing to do is just VTA both through a breather filter but the better way would be running said IM ports to a catch can. Having said that I still use the PCV and a single breather on the hotside of the IM. I never liked the idea of running the hotside port to the intake pipe as that will get the compressor oily. The only upside to running the hotside to the turbo intake would be that it would help suck out the blowby gasses much faster, since running two breathers wont really evacuate the blowby gasses well and it will contaminate your oil faster this way.
I finally took the time to read this through... it’s really good. Should be required reading for anyone planning out their crankcase ventilation. TL;DR version: both vents VTA through catch can for turbo.
I got the JEGS catch can referenced by Sixshooter above. It’s well made. It’s gigantic. I need to make some room in my engine bay for this thing; probably do the Suzuki washer bottle transplant to make some room on the cold side.
After reading that CCV bible, I have proposed two different way to plumb a 3 port catch can. A single 3 port is cheaper and cleaner looking than running dual cans, but should serve the same functionality. Both of these setups are with the PCV valve removed and "B" uses an intake slash cut. VTA still leaves the crankcase with positive pressure. So, which of these would work better?
"A" is a permanent vacuum leak and boost leak. "B" ingests crankcase vapors into a boosted engine, which I'm against for detonation reasons but is the better option of the two.
Better would be leaving that line to the turbo off entirely.
"A" is a permanent vacuum leak and boost leak. "B" ingests crankcase vapors into a boosted engine, which I'm against for detonation reasons but is the better option of the two.
Better would be leaving that line to the turbo off entirely.
I'm actually doing the "B" install now with a 3-port mishimoto can. Very nice and compact for $130 btw!
PS - it fits perfectly at the driver side front of the engine if you make bracket using the hoist hook bolt.
I was under the impression having the turbo pull air from the manifold under boost was a plus. I considered going with a vented catch can like many have mentioned, but doesn't that defeat the purpose? My car is running an FMII and pcv in place with the driver side valve cover vent going to the intake before the turbo. Car has run amazingly well even with getting a little oil into the intake. So by adding the catch can I'm removing the oil issue.
So the way I see it, you can have better air flow from the valve cover by venting to intake, but also get possible vapors. Or vent to atmosphere, but move less air.
Does that sound right?
Edit: The factory car vents both crankcase hoses into the intake. This makes me think it is an even better option than VTA.
10-30-2017, 02:28 PM
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