---------------- CRANKCASE VACUUM TEST RESULTS -------------
Here are the results from tests . The purpose of this test is to assess if and how the oil catch can affects/restricts the vacuum available in the crankcase and thus how the flow of blowby gases is disturbed. I compared the stock setup with a modified version of my catch can install which I'll illustrate below. You'll find all the details hereafter:
1. Car:
1997 Volvo S40 2.0 (normally aspirated engine, not available in US/Canada!)
2. Mileage:
260,000km
3. Oil catch can:
home-made with Husky filter for air tools available at Home Depot. I removed the stone filter inside but kept the plastic "gear-like" ring and the plastic retaining screw.
4. Vacuum measuring "device":
Home-made vacuum gauge with a plastic tube in U-shape filled with water. One end of the tube is "plugged" to the dipstick hole, the other end is opened to atmospheric pressure.
5. Measure:
I measured CRANKCASE VACUUM through the dipstick hole. I tested this vacuum both AT IDLE and AT 2000rpm with and without the oil catch can.
6. Illustration of stock setup:
Here is an illustration of the junction of PCV hose and vacuum sources near the intake manifold/intake duct. This is the STOCK INSTALL:
7. Illustration of the modified junction with the addition of the oil catch can. Basically the Husky filter has been modified to replace the stock part that makes the junction of all hoses. I had to drill the metal cover of the Husky filter and insert a brass tube that would provide aspiration directly from the intake manifold (blue arrow).
8. Results of crankcase vacuum readings from dipstick hole:
Note: the measure is the negative (vacuum) displacement of water ON ONE SIDE OF THE TUBE ONLY!!!! To get the real vacuum these numbers should be multiplied by 2. Since we are only comparing things here, we don't care.
STOCK INSTALL:
- at idle: 7 mm water
- at 2000rpm: 5 mm water
WITH OIL CATCH CAN:
- at idle: 16 mm water
- at 2000rpm: 11 mm water
9. Conclusions:
Two major conclusions can be drawn from the above results:
A) Crankcase vacuum at idle is HIGHER than at 2000rpm!
My understanding of this is that intake manifold vacuum is also higher when the throttle is closed (at idle) so it's fairly consistent. However this may be different for people who have a valve on their PCV system (I don't) as the valve may regulate this differently.
B) Crankcase vacuum WITH the oil catch can is now TWICE HIGHER than stock!!!!!!!!
This is the weird part! I was first thinking that I'd get a lower crankcase vacuum with the oil catch can installed since air has to go trough more bends than with the stock setup. When I tested my first design (which contained much more bends with additive piping) a few weeks ago I got almost NO vacuum at idle. This was consistent with bends in the system causing a drop of vacuum and reducing the efficiency of the PCV system (less aspiration). Now with the new oil catch can design, the crankcase vacuum is twice the one I get with the stock install!!! I have no real idea of what is causing this but I measured this several times and always get the same results! The only thing I can think of is that the brass pipe I added by drilling the Husky filter top is able to create a stronger vacuum in the bowl than what the stock install can achieve.
Basically my catch can should provide a higher efficiency in every aspects: first it condense oil vapors in blowby gases and it is able to pulls more blowby gases from the crankcase, both at idle and under load. This is VERY good...........but is it not causing too much vacuum in the crankcase? Is it sucking too much blowby gases, especially at idle when you don't want to mess with the air/fuel ratio too much (from the readings I may get 2x more blowby gases at idle too with the oil catch can installed)? I'm thinking of adding a small butterfly tap on the small pipe providing vacuum to the bowl (blue arrow) to fine tune the amount of "vacuum" and make it similar to stock conditions (this would be similar to using a vacuum pipe of smaller diameter).
Anyway I would be glad if someone could explain me in details WHY and HOW I get more vacuum with the oil catch can than without it!!!!
This oil catch can thing is getting me crazy!