Should I vent crankcase breathers?
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Road Captain
Joined: Aug 2016
Posts: 696
Likes: 488
From: Southern Indiana
Should I vent crankcase breathers?
I am running a K&N RK-3909-1 High flow air intake system with XiED, to richen AFR, and stock pipes, on my 07 FLSTC, 96 TC motor. https://www.knfilters.com/search/pro...prod=RK-3909-1
As I understand it this filter eliminates the crankcase breathers into the throttle body by blocking the breathers.
Apparently the breather bolts vent into a small cylindrical space but not to atmosphere or tube to ground.
I understand it is good to eliminate the breathers into the intake but is it good to just block the breathers?
Should I install a breather kit to vent to ground and allow the breathers to breathe?
My main concern is overall motor health, I am happy with the performance as is.
As I understand it this filter eliminates the crankcase breathers into the throttle body by blocking the breathers.
Apparently the breather bolts vent into a small cylindrical space but not to atmosphere or tube to ground.
I understand it is good to eliminate the breathers into the intake but is it good to just block the breathers?
Should I install a breather kit to vent to ground and allow the breathers to breathe?
My main concern is overall motor health, I am happy with the performance as is.
Road Master
Joined: Sep 2007
Posts: 1,045
Likes: 74
From: AB, Canada
I would not vent to atmosphere. I would allow the intake to keep the negative pressure on crankcase. This increases ring tension and less blow by. More power. The emissions side of it just bonus for the manufacturer.
Don't buy into the BS about oil residue on your pistons unless you have 50,000 miles or serious blow by issues.
If anything, venting to atmosphere costs you power.
Have a look at other disciplines high performance engines. In the worst case scenario they might add an inline oil separator
Don't buy into the BS about oil residue on your pistons unless you have 50,000 miles or serious blow by issues.
If anything, venting to atmosphere costs you power.
Have a look at other disciplines high performance engines. In the worst case scenario they might add an inline oil separator
Here's a REPORT LINK on External Venting and why it's so crucial for engine health.
Definitely don't want this going back into your engine-
Definitely don't want this going back into your engine-
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Cristy
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Seasoned HDF Member
Joined: Apr 2015
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From: St. Charles, MO
How so? Just curious. I like knowing stuff, and you're one of the smartest Harley guys I know of.
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HDF Community Team
Joined: Jun 2006
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From: san antonio
Not Scott but he will tell you the same; bigger hole will allow more to drain through. Seen too many dynos with breathers vented to a catch can (not sealed so fumes can exit) with no loss of power over internal venting to buy the donk 316 postulate that venting to the atmosphere results in a loss of power. If you "don't buy the BS about oil residue on pistons until you have 50,000 miles" on the motor; check out the attached photos.
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Seasoned HDF Member
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From: St. Charles, MO
Road Warrior
Joined: Mar 2013
Posts: 1,923
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From: Alorton, Illinois
I would breath to atmosphere and not into your engine. When you want all the power. You are wide open. Manifold should be running 100 kpa which equals atmosphere pressure. So, no vacuum on crank case is present. I understand the logic but it isn't needed with PCV valves or the umbrella ones in your rocker boxes. Take away the one ways, and different conversation.