Marty,
this mod ssounds excellent tho i have reservations about long term effects on the motor. Is there anyone that has had this setup on their motor for a long period of time?

 

Ryan,

Look at photo #3 and then photo #4. On the top of the PCV is a little collar that was made from the gas line.

Does that make it a bit more clear?

 

I just did this mod to my klx. Took it for a quick spin around the block and honestly I didnt seem to feel much of an improvement. If anything a slight bit better at around 6500 and up but cant say for sure. Maybe I will take it somewhere that I can really wring it out and should be able to tell a little better. Cant go rippin through the 'hood doin test runs right? Anyway just thought I'd let everyone know that I tried the mod just the way Marty did and the jury is still out on this one for now, but hey for 3 bucks I'm not complaning.

 

For the record I have not tried this mod, but I have a few comments. If a piston moves up and creates a vacuum (a low pressure area), the piston has to have energy “applied� to the piston as it travels up to create the vacuum. To elaborate, the “applied� energy is the momentum stored in the piston assembly and the inertia in the rotating assembly of the crank and rotating parts (rotating assembly). The lower pressure area (vacuum) created will help pull the piston back down after it stops at the top and heads back towards the crank. But there is no free lunch. The force exerted on the piston going up cannot exceed the force the vacuum applied to the piston going down. Even worse, the only source of energy to move the piston on acceleration is the force applied from the burning air and fuel expanding. This energy IS the energy that was used to create the vacuum and later to pull the piston down. Thing is, this energy is better left as momentum than being converted first to a low pressure area, and then back to momentum later.

At best this is a wash from a physics standpoint. Generally this mod just lets air out of the crankcase and not back in. Since there should be a positive pressure in there from the blow by (however small that may be) that isn’t a big deal. Funny however, that the other crankcase mod is reported to allow better flow in both directions of the crankcase vent. This one more than likely restricts flow out and doesn’t allow flow in. If this mod makes a detectable difference (let alone a transformation) then it is a miracle that defies the laws of physics. Worse case scenario is that the valve will be installed backwards or restrict flow so much that it creates a positive pressure in the crankcase that causes seal leaks.

Don’t think I am creating an argument here with anyone specifically. I said my piece. Unless directly questioned I will not post to this thread again. Flame away if you wish.

 

I haven't tried it so I'm just another arm chair general at this point so like all arm chair generals I'll toss in my $.02.

I had the same question, adaycj, a month or so back when Marty first mentioned this. However, after thinking about it a bit, I think I can see the benefit of it. Basically, you are correct, it a wash. But in the previous, no mod case, it is not a wash - the pushing air out and then pulling it back in expends work. Whereas with this mod, once pushed out, the energy of the up stroke is effectively stored in the vacuum created in the engine, and then recovered nearly for free on the down stroke. So in this case, the work is not being expended by pushing the air out of the case through that tiny hole and then turning around a pulling it back in. It is more directly analogous to compressing and releasing a spring - the vacuum being the spring. The net work is zero, so in this case, that is a win because without the mod the net work is not zero.

I'm a three star arm chair general, BTW.

 

Wow! Thats a whole lot of technical jargon there guys, but what you guys have said makes sense to me some what. Since I am not a mechanic I cant say either way whether or not this can benefit or a harm the little 250 motor. If worse comes to worse it can be undone in a matter of 5 minutes, but does anyone REALLY Know?

 

I'm looking analytically like adaycj & Nobrakes ... basically what it seems to be doing is STOPPING the piston from pumping air back and forth through the breather tube, almost undoing the effects of 3/8" airbox drill mod. So if the PCV valve is one-way, you have negative pressure under the piston, and basically NO airflow through the airbox -- so is the power gain from NOT losing it by moving air back & forth through the airbox??? If so, then the 3/8" airbox drill mod should actually HURT performance, but everyone seems to agree that it helps it, so what's going on?

One positive aspect that I can see is that with negative pressure in crankcase, it should increase the pressure difference with respect to the oil pump and increase the oil flow. I find it hard to believe that it would even be noticable, though.

I'll stand on the sidelines on this one and wait to see what others experience before I shell out my hard-earned $3!!! [sm=smiley2.gif]

Mike

 

Why aren't the engines set up this way from the factory?

 

The factory is under strict guidelines to put all this polution Junk on the bike. Although after I think of this Mod a while I do no that this is the only breather on the engine. So making the breather hole larger helps by moving the air in and out faster. Now the IN part is what I'm concerned with as you push the air out it also needs air to come back in just as you body does. A vacum pump works different from a pcv valve a pump pulls air out of the motor all the time BUT the motor still has a breather somewhere to let air come in and out . Air has to come into the crank case from somewhere. Now putting a pump on moves it faster. Just as on cars with this valve most of the time there is a PCV valve on one valve cover and a Breather on the other one.
The way racers do it is run a breather to your exhuast header and come into the pipe on an angle and when the exhuast passes by the tube at a very high rate of speed it also pulls gases from the motor.
There are many ways to do this but if a motor has only 1 breather I feel you should have it going in 2 direction IMO........
All of this might not matter at all but I do no that the mod of drilling the air box helps I drilled mine to 1/2" ...... K&N sells a small crank case breather we used to use on all the Breathers lines just clamp it into the hose coming out of the motor. The air box ide is done so that the carb pulling air through it helps pull gases from the motor ... The only problem with that is your sending hot gases back in the carb and cool air works better. But the EPA wants it reburned
So I'm tired now from all this thinking

 

oops, duh!!