When I was researching why throttle bodies get dirty, I learned all about the PCV (positive crankcase ventilation) system and how they remove the "blow by" gasses that push past the piston rings during the power/combustion stroke.

I have also read that an "open catch can" (vents to atmosphere via small K&N like filters) will reduce crankcase pressures.

Well... That got me thinking and I wondered how much pressure is in our crankcase? Does it change with engine load, engine RPM or both?
If I "open up" my PCV system, will the crankcase pressure be higher or lower?

I had to find out and so I built this crankcase pressure data logger that records the crankcase pressure 10 times per second to the SD card (along with date & time)
Now, it is time to start to collect the data

Below is the setup that is going to be used:

 

this is knowledge only a handful of individuals know about. The oem system stays a low vacuum at idle then tries to keep it at part throttle. The judge here is the PCV valve, ideally you want to keep it at 0 or slight vacuum at all times but being that the pcv works only under vacuum it can't.

Vacuum in the crankcase will provide better sealing of the rings along with higher life expectancy of seals. I'm excited to know results, this way you can finally decide on what type of system and routing will actually work for the g37 and not just blind trust on price and brand.

Hats off to you sir!

 

Maybe jumping the gun here as I just noticed the Arduino reading. Is this KPA reading correct on this? If so HOLY MOTHER, translates to 14 psi in the crank case.

I dont know how many methods you plan on testing however you should consider:

Idle, part and WOT for all
Factory
All open to atmosphere
Breathers to atmosphere with PCV factory
PCV to atmosphere with breathers connected to factory
Adding a bigger volume source of vacuum
Adding catch cans between pcv

From your videos you probably have all of this in mind, cheers and thanks again

 

Thanks
Based on data from a few data logging runs, everything you said is spot on!

The measurement shown is in absolute pressure (relative to absolute 0 pressure), not gauge (relative to current barometric pressure). In that picture the engine if off and it is showing the barometric pressure.

Since that picture was taken, I have added a second pressure sensor to measure the barometric or air pressure around the car.
I updated the software to calibrate both sensors, and now only display/data log the crankcase gauge pressure in mBar.
This will prevent elevation or weather from changing the reading.

Thank you for your testing suggestions!
We do think alike and the testing will be underway as time permits.

 

I learned about this in the racing world with built engines with big ring gaps end up creating a lot of blow by they install vacuum pumps to pull vacuum on rings and essentially let you run additional boost. I learned that pressures can cause additional strain and will eventually start popping seals. After first gen G35 introduced me to an inefficient PCV system I decided to do some research on improvements, I also own a g37 and the system has definitely improved however I believe it can be improved upon just dont have sufficient data.
I read that venting your crankcase can cause cause a drop in MPG which is understandable along with an increase in temperatures which I'm not so sure about.

 

Hello there, have you had the chance of recording some of these pressures? looking forward to these.

 

I haven't forgotten about you BULL!

The data logger is now on hardware version 3 and I am on the 4th different pressure sensor... all in the name of accuracy and speed - which I now have
I have 6 months of data to organize and analyze of different driving conditions, temps, with factory PCV and with a vented PCV.
-INCLUDING- the 8 runs at wide open throttle in the first 4 gears while at the drag strip.

This updated version records these inputs, 80 times per second:
• Engine oil pressure
• Engine oil temp
• Engine RPM
• Crankcase Pressure
• Fuel Pressure
• Differential oil temp
• Manual trans oil temp
• Power steering fluid temp
• Local air temp, pressure and humidity

I expect the first episode to be out in July.

 

Reading this made my day

I've been intrigued by Crank case ventilation since I learned about vehicles. Back then I spent a lot of time at drag strips and couldn't help but notice air pumps directly to valve covers. After learning the reason behind this and the flow of these pressures I understood there is potential for power and efficiency in that area and how ignoring this particular area could lead to engine issues. Some of these transformed to fittings welded to turbo intakes and exhausts in angles to produce a vacuum effect thus relieving these pressures at higher RPMS relieving some of the load on the rings produced by the backing up of this pressure.
I noticed on the VQ37 the breather plastic fitting that goes in the intakes their ends are cut in angle for this effect to help scavenge these.

I figured if done correctly it would produce quite a bit of data, data that you want to reproduce + multiple configurations must have been a fun time.
Data alone should make great video content.

Could you imagine if people are making blow by issues worse by venting pcv?

P.S where do you get that TX cable in your area?

 

What do you mean by "TX cable"?
The cable used for data logging is a shielded, 18 AWG, with 4 conductors. This allows 2 sensors per cable.

 

TX as data. Shielded.

I see a few connectors there looks like they could potentially be pressure sensors. Anything you can disclose as of yet?

 

BULL,
Sure... some pressures are higher than expected and some drop lower than expected

I have a lot of raw data to analyze and verify, and I don't want to jump to any conclusion until that is done.
Then write the script, shoot video, record voice over and then all will be told.

Question for you.
From the list below, what are the top 5 most interesting to you?
• Engine oil pressure
• Engine oil temp
• Engine RPM
• Crankcase Pressure
• Fuel Pressure
• Differential oil temp
• Manual trans oil temp
• Power steering fluid temp
• Local air temp, pressure and humidity

 

• Engine oil pressure 8/10 - this is a life changing one. After discovering my Gallery gasket failure I wished I could have monitored this better. I know the 350z brought a sweeping pressure gauge, the 370z brought a sweeping temp gauge. We know thanks to your torque PID we can tap to the factory temp switch however I wonder if we could do something similar using the 350z switch.

• Engine oil temp 10/10 only After your Torque mod. Brought a lot of awareness to my driving and showed how slow the engine oil temp control can be without a cooler.

• Engine RPM 1/10 Dashboard provides most of the necessary info

• Crankcase Pressure - 8/10 Mainly because we dont know. I know this system changes from vacuum to pressure and vice versa. It's meant to carry gases and separate these vapors properly. As we see many are promoting the deletion of this system mainly because they dont understand it, dont care for it, have been sold on that this is the only fix to stop oil consumption.

• Fuel Pressure 5/10- as you get faster and start tuning this become more important due to the return less system. You'll be able to monitor these pressure, of course any dips will mean you might need to visit your fuel pump/strainer sooner'

• Differential oil temp 4/10 - it would be a good idea to find out factory baseline to determine if these covers are really necessary. Overall this is a small space surrounded by thick metal that should overall not need much maintenance. wear should be slow and if it is temp show follow suit also. I feel like any rise in temps can be controlled with the correct fluid and that most folks wont benefit fully from these covers.

• Manual trans oil temp 2/10 - For the most part no one has complained of this. Overall, the CD trans does a good job temp control

• Power steering fluid temp 3/10 - Nissan switched to ATF in their newer vehicles so it would be a good idea to compare average temps between regular driving and spirited to determine how does the factory cooler holds up.

• Local air temp, pressure and humidity 1/10 - The car brings local outside temp that is not too far off. Humidity can be searched on your phone.

 

^^^
BULL, thanks for this well explained and comprehensive list, I appreciate it.

I want to point out that the "Local air temp, pressure and humidity" is mostly for calculating local air density. This is useful to calculate the *real* correction factor (SAE J607 & J1349) when at the dyno or drag racing. From what I have seen, most dynos don't have accurate weather stations at the shop - they use their phone.

If you use your phone, the pressures are corrected for seal level and the temp & humidity can vary a lot as the local weather station is likely miles from your location.

Thanks again for the input. I've got to get back to working on the next episode

 

Interested to see the results and the video. Sub'd.

 

Subbed. This is interesting stuff - did similar with old Pic Micros and sensors in the early aughts to make data recorders for the racecar. FWIW, the pc-board mount pressure/vac sensors used in the old Megasquirt standalone ECUs were inexpensive and very accurate, but they had to not be in the engine bay, or very well shielded from heat. Our experience using electronic gauge sensors and OEM MAP sensors from various cars showed they had a built-in time filter - that is, they reacted very slowly in electronic terms to changes in the measured pressure. For measuring cylinder pressure rapidly we ended up using a lab-grade stainless sensor that cost hundreds - thank goodness we only needed one.

For this project, I'd like to see if passing the PCV through a oil/air separator (basically, the drain bottles everyone is using with some steel wool added) then back to the intake changes the pressures and performance substantially.

Pressure v. RPM and engine load (I guess derived from injector PW) would be interesting to see plotted out.