2000 Civic SI Build
Crank Evac System and Theory
Background - I
spent many months and a lot of money trying to correct oil burning at
higher RPM's. I started out thinking it had to be rings, then it had to
be valve stem seals, then this and that. This page will give you the
steps I went through that corrected my oil containment problem.
From what I understand, this may not be legal in some states as
some of the modifications may affect your emissions. Check your local
laws before you proceed. Where I am it doesn't matter.
There are a number of steps that work together to stop or
greatly reduce the oil burning in your high rpm Honda. There is also
quite a bit of theory behind it. So follow along. This is the exact set
up I run in my boosted 2000 SI EM1 running 19lb boost and 314hp of
nitrous in 2 stages.
Pressure on the top side (cylinder head side) of the
pistons is good. While
rings do have to be gapped correctly, the ring tension alone wont seal the
cylinder. Its the pressure in the combustion chamber forcing the rings
down, and out, that seals it up.
Likewise, if there is too much pressure on the bottom (crankcase) side
of the piston, the rings cant press down and out as hard, and they wont
seal the combustion chamber properly. The two pressure forces are
fighting each other.
When your car is stock, crankcase pressure is relieved by vacuum in the
intake. As the engine is running it creates vacuum. There is a hose
from your pcv breather and valve cover that connects to the intake / cold air piping.
When the motor is at idle, or freeway cruising (times of high vacuum),
the vacuum actually pulls the pressure out of the motor
allowing the rings to seal, but, at the expense of a contaminated air /
fuel charge, which, hurts horsepower. Under acceleration (times
of low, or no vacuum, or when building boost) the pressure builds
in the crankcase and IS NOT pulled into the intake due to no vacuum.
This can be a big problem for those who are running turbos or
superchargers as the crankcase pressure has no way to escape.
This is the time where the rings may not seal properly and you get some
blow by and oil consumption. Many people try to relieve the pressure by
using a small filter off the original valve cover breather hose. This
typically wont solve your problem and can leave an oily mess on your
So, you basically need two systems to
keep the crankcase pressure low. One for high vacuum conditions, and
one for low vacuum conditions.
The system on my car is a sealed system and consists of removing the
stock pcv breather, plugging the large hole with the kit from Z10
(shown below), pulling one of the big allen plugs on the back of the
block and installing the AN adapter into the hole. I use only one -10
AN line coming from the breather hole closest to the transmission end
of the block. This leaves more room to get at the oil filter.
In the first
you can see what the Moroso Oil / Seperator looked
like originally. There is a small fitting on the right side. This was
ground off, tapped, and plugged. I welded three aluminum bungs about 1
1/2" above the larger fitting on the left (close to the top of the can) allowing
my to run my three 3/8" x -8 AN fittings for the valve cover breather
tubes (one bung is not currently being used). The big -10 AN fitting on
the left side is connected to the breather line that comes out of the
back of the
block. This line works as both the breather tube and an oil drainback
tube back to the block. By draining the oil back you don't have to
worry about the canister filling up with oil and having to drain it. My
car is a daily driver and the last thing I want to do on a trip is have
to stop to drain oil out of the oil / air seperator. The AN
fitting on the bottom of the oil / air seperator is for the crankcase
evac system. I used a Moroso part number 25900. Its designed for a V8,
but will give you an extra set of pipe and check valves in case you
change your exhaust or the valve goes bad (I have to replace the check
valve every year or so and get replacement valves from Napa). The two
breathers shown at the top of the picture and the rubber grommets shown
on the left are not used in my system. Drill a hole in the exhaust pipe
your catalytic convertor (if you still have one) and weld the angled
tube in at a 2 o'clock to 3 o'clock position. Make sure the
angled part is aimed toward the back of the car and the angle cut is at
90 degrees compared to the exhaust pipe. Screw one of the one way air
check valves onto the welded in pipe and tighten down. Now connect the
-10 line from the bottom of the oil/ air seperator to this. I just use
a hose clamp to hold it onto the valve, this way its easy to remove if
you need to drop the exhaust.
On the valve cover I use the original breather tube hole on the
backside of the cover, but I have pulled the vent tube out, tapped it
and installed a -8 AN fitting. On the front side of the valve cover I
have drilled and tapped two holes for AN fittings. The one on the front
passenger side will go to the Morosso oil / air seperator. The hole
with an AN fitting on the front drivers side will go to a KrankVent.
This is a top of the line one direction PCV valve. I used their universal vent with a
1/8" NPT female thread. Cost was about $100 (you dont need the $239 kit thats shown). The KrankVent is vented to
So, connect it all up and this is what happens:
At idle or low RPM driving there typically isnt much exhaust volumn.
Therefore the one way air check valve on the exhaust pipe wont open or
will only open part way. At times like this the engine can relieve
crankcase pressure through the KrankVent. This keeps low pressure in
At higher rpm, or under boost, there is sufficient exhaust volumn to
create a negative pressure and open the one way air check valve on the
exhaust pipe. This in turn uses the negative pressure to pull the
pressure from the Moroso oil / air seperator, which in turn pulls it
from the crankcase and valve cover area. During this time the KrankVent
closes and all pressure is relieved through the evac system
Now you have low crankcase pressure at low rpm, and low crankcase
pressure high rpm and your oil comsumption will be reduce. You may also
pick up a couple horsepower as a result of not having a pressuriaed
If you have Questions or comments feel
free to email me