Explanation - KrankVent what is it and what is it meant to do?

Posts: 17
Joined: Sun Feb 08, 2015 5:05 am

Explanation - KrankVent what is it and what is it meant to do?

Postby Justin » Sun Feb 08, 2015 7:08 pm

OP: http://www.mazda3forums.com/showthread.php?t=407691
Whats a KrankVent:
The krankvent valves are designed to make the interaction between the crank casing and the intake operate more efficiently, in doing so making your engine more efficient and perform better (supposedly). That said the two big +'s I see are
block boost from entering the crank case ( Valve train area)
block/reduce blow back while under boost ( from the engine thru the PCV to the Intake)
What is it meant to do:
NOT ON BOOST and NA: Basically equalizes pressure and promotes crank case vacuum.
Air/fuel mixture is blocked from entering crank case.
Oil & fuel is no longer blown into intercoolers, intake tracks, fouling plugs
In short the boost does not leak into parts of the engine u don't want it to be in
Maintains Crank case vacuum

Have a read: of
the post from TVissues on http://www.mazda3forums.com/showthread.php?t=395784 (and Below).. basically he describes all of the issues he had prior to the install of the KrankVent and compares it to his post install observations.. most striking is the catch can... went from full of oil to almost no oil! being caught...
this thread by 222speed3 - http://www.mazda3forums.com/showthread.php?t=396792
Also I think Tabasco, and I cant find the posts, did something very similar if not identical. He observed that there was a fair amount of oil mist being pushed out by the breather hose. His solution - Install valves into the valve cover... ( i am running off memory on this one so if im off or even right please let me know and ll adjust)
tvissues POST
sorry i'm late here but i haven't been on here in two years. Thought this was a known fact by now....

Basically, the issue with these vehicles from the start is the crank case ventilation system. i used to own a 2007 ms3 gt. Had every performance part you could have on the thing. had the motor blown and rebuilt. Even after the rebuild i still had oil coming out of the valve cover, cycling through turbo and intercooler and through the motor. even after calling performance shops and going through 4 turbos (two factory, two gt3076r's) i finally figured it out. First off all need to know that the pcv valve under the intake manifold venting excess pressure from the crank to the intake mani is supposed to be apart of a regular maintenance, meaning replace it about every 1-2 years.

The issue that these motors have had since day one is the fact that the pcv valve used on the disi mzr motors is the same exact one used on the n/a motors. If you don't know what that means well you have to know how a crankcase ventilation system works (what its supposed to do). When your motor is at idle, your intake manifold is under vacuum, this is true for both n/a and forced induction (turbo/supercharged) motors. At this time the tube connecting your intake manifold to the crankcase, containing the pcv valve, is in vacuum. This means it is providing vacuum to the crankcase as well. that is how it is designed. Now, as an n/a motor climbs in rpm (throttle opens) the pressure of the intake manifold is always in a vacuum. In fact it increases in vacuum, as this happens the vacuum pulling gases from the crankcase increases as well which is desired. The purpose of this system is to remove excess pressures that leak by pistons. There will always be some form of leakage in pistons, this is normal, this is the purpose of the cvs (crankcase ventilation system). the purpose of the pcv valve is in the event there is a backfire (positive pressure from an explosion exiting back out of the intake manifold) the pcv valve will close preventing an explosion igniting the possible fuel that has leaked into the crankcase.

The difference with the disi mzr motors is that our manifold does not stay in vacuum upon acceleration. even under cruizing conditions as the turbo climbs it is applying positive pressure into the manifold reducing the vacuum caused by the cylinders as the motor operates. this can be seen on anyones boost gauge as they start to accelerate. Herein lies the problem. if for example at WOT the pressure in your intake mani is 15psi, your pcv valve will be closed preventing pressure from the intake mani pressurizing the crankcase, it does good at these high pressures. Well while the motor is under WOT this is the time when the crankcase will be introduced to the most pressure leakage from the cylinders due to the higher cylinder pressures. this is where the valve cover vent comes in as a back up releasing excessively HIGH pressures from the case under WOT conditions. in other words the valve cover vent is an exit only. Now, lets say your cruising on a highway and start to climb a hill. As you climb the hill the turbo will slowly spool up and start to provide positive pressure to the manifold. Lets say your crankcase is at 5inhg but the gauge which measures the intake manifolds pressure reads 2inhg. This means the manifold is now at a higher pressure level (positive pressure) than the crankcase. Again, the tube is open to the crankcase from the intake manifold, the problem is the factory pcv valve is built to stop abrupt, explosive changes in pressure. if you remove the pcv valve and try to close it shut by blowing on it with your mouth you shouldn't be able to close it unless you've had some good practice in blowing things... point is i couldn't even get the valve to close, i don't know the exact pressure a set of healthy human lungs can exert but i know one thing, if the crankcase has a higher level of vacuum than the intake mani, the cvs is not doing its job if the differences are below its closing threshold. What results is at least ~1-2psi entering the crankcase before the pcv is able to shut.

One might ask, what difference does it make if there is a little extra pressure down there? Well this is the problem, when that valve finally closes, lets say 1psi gets in, as the motor is running and gaining pressure from the cylinders,the pressure level in the crankcase increases. What about the valve cover? Well if you look at the bottom of the cover its baffled, not to mention has only a few holes to balance between the head and crank. Now the turbo as some know and others don't, has an oil gravity drained system meaning pressurized oil feeds the turbo bearings but the oil is gravity drained into the crankcase. if there is 1psi or any positive pressure pushing against the oil do you think it will drain? keeping in mind i couldn't get the valve to close with my lungs, if i was to blow on a straw filled with oil it would go right out the top. Now if i also put my finger on top (pressure from the oil system feeding the turbo) the oil would not move, it would not drain into my mouth. this leaves one place for it to go, the turbo seals and the end of the shaft and bearings hence your oil leaking from the compressor wheel even while its not running.

So, how did i fix this? simple, since the pcv valve doesn't close fast enough i got some additional valves (keep the pcv for extreme pressures like backfire) and put them inline of the cvs before the pcv valve. these valves will instantly spring shut when both sides have equal balanced pressures. what this means is as you decrease the negative pressure in the intake mani (vacuum) when the pressures in the intake mani and the crankcase are equal the valve will close preventing excess boost pressure from going into the crankcase. the other valve will go inline of the valve cover vent to only let air out not in, this will provide the perfect operating conditions of nearly 100% vacuum at all times of operation of the motor. Now i know that it will still have some build up from cylinder leakage under WOT conditions but with each shift the new valve will instantly open during the split second your mani is under vacuum (gauge might not show it since it happens very fast) and drain any excess pressure from the crank.

after 3 years of having this problem with my intercooler filled with quarts of oil, dumping several quarts from my catch cans, going through turbo seals, having clogged injectors due to the burning of oil, I finally figured it out and I knew i did because i tried my best and put 2k miles on that thing over a week and a half trying to reproduce the problem only to find a neat surprise when i pulled the dipstick on the motor while it was running. Everytime i pulled it i got a nice crisp whoosh of vacuum from the dipstick tube (that's why it has a seal on it) and from then on never got a drop of oil in either catch can only fuel vapors in the lower catch can (cvs) like its supposed to do.

As far as the the piston failure, well

Boosted baby....


Last edited by okellyr; 11-30-2012 at 11:20 AM.

Return to “Automobiles (Turbo)”

Who is online

Users browsing this forum: No registered users and 1 guest