So I've done some research on the breather hoses and re-routing them etc to prevent oil blow by and so on. Well, I just purchased a new air cleaner kit from fuel moto (looks great) and noticed they have the hoses routed back into the throttle body. Now, from what I understand this is harmful to the engine. And although, I dont have any "blowby" or oil leaks in the filter, is this the best place for the hoses? I get the clean air/dirty air thing but, how much of a difference does it really make?
Does anyone have any experience with doing it one way or another, and positive performance gains, or noticed premature engine wear due to leaving the hoses routed in? I've been pretty curious about this, and want to do it right the first time. Its new motor I want to keep strong so, any advice and experience is greatly appreciated.

 

On your '12 Bob it will make zero difference piping it into the throttle body. Unless you over-fill the oil there will be only a tiny amount of oil in the gasses being recycled; this will do no harm.

Older engines that are producing a lot of blowby (and so really need fixing anyway) could perhaps benefit from piping the head breathers away elsewhere. But then you have the problem of what to do with the oil and so its usually fine just to leave it as it is because even a moderate amount of oil in the blowby will do no harm to a Harley engine.

 

I would think with a carb bike there would by enough fuel/air mix in the intake manifold to dilute the oil vapor and it doesn't seem to hamper the combustion process. I have a 2002 carb and a 2005 EFI with open intakes and stock oil vapor returns. Neither bike has yet to develop the dreaded oil streaming down the side of the bike or on clothing. I was I knew what I was doing to prevent this, if I did I'd pass it along. I do inspect the oil vapor return hoses when I oil the filters (once a year).

 

Is it true that with the hoses routed back in you lose a big chunk of the performance gain you would otherwise get from a new air cleaner?

 

No. Makes zero difference to performance and don't believe any snake oil that says otherwise.

 

From my experience the supposed performance gain is not noticeable. I've installed filtered breather bolts in place of breather hoses on two of my bikes and noticed no performance gain. The only thing that I did notice was a mist of oil on my engine and pipes that I need to wipe down after riding. If I was doing it again I would save my money and stick with the breather hoses.

 

Thanks for the speedy responses guys. Looks like I wont worry about rerouting anything. I'll be installing the tuner tomorrow morning, then I'll do some pics and a test ride.

 

Not too long ago (when engine tolerances were Tighter at HD) everyone routed the dirty oily hot air into the atmosphere. It has only been in recent years that it has become commonplace to put that nasty air into the combustion chamber.

It affects every bike differently, there are so many variable in oil, riding style, etc. Some have 100k+ on their bikes and they are running top notch, others experience significant carbon build up.

How many times have you read on the forum here of guys who's bikes have been running great, they have not done anything to them, but all of a sudden they notice their bike pinging? Many times this s because there has been carbon build up, increasing the compression ratio, and what once was a good tune no longer is because they have an effective increase in compression.

It is impossible to know if your bike will run perfectly fine for 100K+ miles, or if you will experience carbon buildup in your cylinders. What is possible to know is that if you don't feed that in, you for sure are not causing possible future issues.

Regarding power, NRHS has published dyno's showing a consistent 3-5% increase in power by NOT feeding hot oily air into the intake. Whether that is felt in seat of the pants or not varies from person to person.

Again, it is only in recent years that what was once commonplace knowledge, is no longer.

Engines run better with cool dry air going into the intake. Putting hot wet (oily) air into the intake reduces performance.

We have observed this hundreds of times on dyno runs and in the seat of the pants. We never bothered saving/publishing these because in the not so distant past it was sorta like reminding people that the sky is blue...it just was not necessary.

In the next month we are going to put a 2012 103ci on the dyno. We will be recording and publishing dyno's showing the difference between routing the hot dirty oily air into the intake vs. into the atmosphere.

NOTE: EPA requires the breather air to go into the intake tract. If you choose to route it into the atmosphere, that is an "off-road" set-up and not technically legal to run on the street.

 

LOL...Not that long ago! My 86 FXR had the hose routing into the Air Filter, so its been around for a few years.

 

I think the tricky bit is knowing when you need to start to route the breathers from the A/C.

On my old Sportster the umbrella valves we none too good and it slobbered a bit. I knew this because there was oil inside the air cleaner; running the engine with the hoses from the breather ports off I'd get the odd drip of oil. I definitely didn't want this fed into the engine, it was going to cause carbon build-up so I piped it off to a catch can.

With my 2010 Fat Bob there is nothing at all coming out the breather ports. With the pipes disconnected from the A/C there's not a drop comes out, even after a hard run. I've pulled the pipes off and checked. So I'm happy to leave it with it breathing through the A/C.

Reason I am not in a rush to pipe it away from the A/C is cos of the potential mess. You can get a mess down the bike or your leg or you have to empty a catch can or you can even have oil heading towards your rear tyre.

As for performance....Funny you should mention NRHS. I remember them testing crankvent valves and finding they made no difference to performance and this was comparing them to feeding the breather ports to the A/C. So I'm confused that you say they found a performance benefit with non-A/C breathers.