NAVY8TR

The crankcase emission control system. I'm talking bout the funky looking hoses and clearish box in the lower part of the airbox. I only found one thread on here about it and I am surprised. from the sounds of it is seems like if you plug the system you build too much pressure and can really f-things up. but what if you just re-route the hoses so all you get going into the carbs is fresh air? Has anyone done experiments? what do you have to say about it?

RCVTR

You'll coat the inside of your crankcase and everything in it with burned oil and other hydrocarbons.

Routing it to the airbox keeps the crankcase ventilated. Positive crankcase ventilation (PCV) is your friend.

jbaxx

Whatever you do, DON'T PLUG IT! Best just leave it alone - nothing to be gained.

VTRsurfer

+1

The PCV system actually lengthens engine life by reducing HC and water vapor contamination of the oil and preventing sludge formation.

JamieDaugherty

Yep, no gains to be had there - just issues. Leave it alone. I love changing stuff and mines still in place just like stock.

mboe794

Your right...some thoughts have crossed my mind. I've seen some engines that just have some sort of filter at the end of the hose, rather than ending in the airbox. I always thought it would be beneficial to allow only fresh air into the carbs but not eager enough take any risks by messing with it.

john3012

I have seen the filter at the end of hoses too. Mostly on dragstrip ATVs owned by rednecks. BBW - Just because you see it doesn't mean that it is right.

RCVTR

Yes. Water and CO2 are the primary products of hydrocarbon combustion.

Water will condense in the crankcase when it cools, if the concentration is high enough.

drew_c14

Absolutely nothing to be gained by doing this except maybe a leaner running engine. The blowback gasses don't have to route back the way they do, it's just an emissions thing. But they do have to go somewhere...

autoteach

So, had a customer that did some engine work on his own. We had to go back in for them to fix some top end issues. We gave it back and he complained that it had no power. In lots of diagnosing, we found out that he some how eliminated the crankcase ventilation, meaning that with the spark plug out, it was still "compressing" air. It sucks major dong. He let us know after that he may have ventured into the bottom.

Moto Man

Would venting the gases away from the airbox help keep the air/fuel mixture cooler, denser, and more oxygen rich?

Does the system need the draw/vacuume from the airbox to ventalate properly?

JamieDaugherty

I doubt it. You are talking about a very tiny amount of air compared to whats flowing through the airbox already. I doubt you would ever be able to tell the difference.

I think one of the big purposes for this system is to maintain a vacuum in the crankcase. This reduces pumping losses on the bottom side of the pistons and also improves ring seal.

gboezio

It's going to the airbox to recover oil vapors, otherwise trough a breather it let the blowby gases out and let the underside of the piston breathe, both pistons go down almost at once, it displace a heck of a lot of air, remove the oil cap while idling you can feel a lot of air going in and out. An I4 for example displace almost nothing because 1-4 are opposed to 2-3 so the air just move under the next cylinder and is not forced out like a twin.
It's one of the V-twin fuel inefficiency factor.
Vacuum PCV is the best, but on the SH it's plain atmospheric pressure.
As for gains, very little, very very little, unless you forgot those rings on the counter, then it may helps

Oh and yes I have seen breathers somewhere, it stinks oil vapors