New Crankcase Ventilation System for POD Filters

I'd really appreciate any feedback on a system I put together while working on my KZ.

After removing the OE air box, installing POD filters, and adding a small filter on the crankcase vent, I realized all the drawbacks. Originally a tube from the crankcase vent to the air box allowed blow-by gasses to be drawn into the box, through the carbs, and into the engine to be re-burned. This prevented fumes and smoke coming up from under your seat, reduced harmful emissions output, ventilated the crankcase to reduce oil contamination, and higher crankcase pressure. Now with the PODs, the OE crankcase ventilation is lost. The small filter on the vent does nothing but prevent dirt from entering the crankcase, while blow-by gasses go directly into the atmosphere (under your seat).

I couldn't deal with it. So I used tubing, Tee's, elbows and grommets to create a network connecting the crankcase vent to each POD filter, and replaced the OE ventilation system we lost. I took my time and was careful to maintain unrestricted vapor flow evenly distributed to each cylinder. And It works just like the OE vent system did originally.

Again, I'd really appreciate any and all feedback, good or bad. Thank you...

With a hose running to the ground, there should be very little or no smoke visibly coming out after the bike is warmed up. If there is a lot, I would have to wonder why. Most of what comes out is steam on a cold day, so I like the hose for routing the water down to the ground.

Thanks loudhvx.

There will always be blow-by coming out the vent. Combustion gasses getting past the rings is normal on any and every engine. That's the reason behind a PCV system on every car engine.

Seeing smoke will depend on the condition of the rings and cylinders, plus the engine's compression ratio. Higher compression engines produce more blow-by. Huge amounts with a turbo or supercharger because of the greater pressure.

The only advantages I see using a hose from the vent to the ground is it may keep the blow-by away from your face, and a slight draft while moving, but no negative pressure drawing the blow-by from the crankcase at idle. When the engine heats up any moisture in the crankcase will vaporize and rise out of the vent. If you see water droplets coming out the hose at the ground, it's gotta be due to the moisture condensing in the hose.

That is a smart idea, I ways thinking about something like this myself.

On the 750, the 1 and 4 pods are actually touching the frame and sidepanel, so attaching to the pod at the rear might be a problem.

The vac take offs on the inlet manifolds could work but they are very small diameter pipes. Maybe fitting bigger nozzles might be possible, just really we want to be recirculating pre carburettor.

Did you notice any difference in performance/oil/fuel consumption in any way after this mod?


During World War II a different type of crankcase ventilation had to be invented to allow tank engines to operate during deep fording operations, where the normal draft tube ventilator would have allowed water to enter the crankcase and destroy the engine.[4] The PCV system and its control valve were invented to meet this need, but no need for it on automobiles was recognized.

(no need was recognised at the time)

en.wikipedia.org/wiki/Crankcase_ventilation_system

Interesting set up. It certainly appears that the vapors will be pulled back into the system. My only thought (I am not claiming any expertise about this) is that something makes me think the closer pods (2 and 3) would receive more of it than the outer pods. Not sure if this would have any effect on mixture / jetting or not.

Tyrell Corp wrote: That is a smart idea, I ways thinking about something like this myself.

On the 750, the 1 and 4 pods are actually touching the frame and sidepanel, so attaching to the pod at the rear might be a problem.

The vac take offs on the inlet manifolds could work but they are very small diameter pipes. Maybe fitting bigger nozzles might be possible, just really we want to be recirculating pre carburettor.

Did you notice any difference in performance/oil/fuel consumption in any way after this mod?


During World War II a different type of crankcase ventilation had to be invented to allow tank engines to operate during deep fording operations, where the normal draft tube ventilator would have allowed water to enter the crankcase and destroy the engine.[4] The PCV system and its control valve were invented to meet this need, but no need for it on automobiles was recognized.

(no need was recognised at the time)

en.wikipedia.org/wiki/Crankcase_ventilation_system

I've seen that interesting piece of PCV history before. Really interesting.

The difference between bike and car PCV (Positive Crankcase Ventilation) systems is that car engines use manifold vacuum to draw the blow-by gasses out of the crankcase, with a PCV valve to regulate vacuum under given engine speed and load, and they also have a breather on the other side of the engine to allow filtered/fresh air in -- while pulling the blow-by out. I'm assuming bikes don't use this system because there is no common intake manifold, and/or a lack of adequate vacuum.

I believe you're talking about doing something similar on your bike using four vacuum ports. The only problem I see is designing a valve(s) to regulate the vacuum, if the vacuum source is even sufficient. Remember you can't just take the caps off those ports because it will cause an extremely lean condition. I thought about that, but it seemed way too complex as opposed to just replicating the OE ventilation system using the negative pressure from the intake air, as opposed to manifold vacuum.

As far as fitting the elbows at the back of your PODs? If they're hitting the frame they're the wrong size to begin with. K&N has a big variety of POD sizes and shapes to chose from. I'm pretty sure you could find the right size to clear the frame and add the elbows.

I was jetting my FCR35s with a dyno before and after install, and didn't notice any difference. Remember, these gasses being burned up by the engine is how the Kawi engineers designed it.

Interesting set up. It certainly appears that the vapors will be pulled back into the system. My only thought (I am not claiming any expertise about this) is that something makes me think the closer pods (2 and 3) would receive more of it than the outer pods. Not sure if this would have any effect on mixture / jetting or not.

I think this might be a factor - I wonder maybe just recirc to pod 2 and 3? I know the early air cooled Suzuki GSX and some kz had differing jets between inner and outer pots to compensate for temp differences.

I guess the crankcase gases would be lower in 02 but with some unburnt hydrocarbons, so let the middle pots have this?

Maybe even alter the diameter of the nozzle or pipe for 1 and 4 furthest away from the breather?

Good thread, keep it coming.

gd4now wrote: Interesting set up. It certainly appears that the vapors will be pulled back into the system. My only thought (I am not claiming any expertise about this) is that something makes me think the closer pods (2 and 3) would receive more of it than the outer pods. Not sure if this would have any effect on mixture / jetting or not.

Very good point! Here's a better picture below. I made sure that there is exactly an equal distance of tubing from the vent to each POD. This keeps an equal flow of blow-by to each cylinder. I was also careful to maintain the ID of the vent port throughout the network. The output ports on the Tee at the vent are 1/2 or greater than the OE vent ID, and so on with the Tees between the PODs.

Again, tuning on the dyno I saw no difference in air/fuel mixture before and after install.

Tyrell Corp wrote: Interesting set up. It certainly appears that the vapors will be pulled back into the system. My only thought (I am not claiming any expertise about this) is that something makes me think the closer pods (2 and 3) would receive more of it than the outer pods. Not sure if this would have any effect on mixture / jetting or not.

I think this might be a factor - I wonder maybe just recirc to pod 2 and 3? I know the early air cooled Suzuki GSX and some kz had differing jets between inner and outer pots to compensate for temp differences.

I guess the crankcase gases would be lower in 02 but with some unburnt hydrocarbons, so let the middle pots have this?

Maybe even alter the diameter of the nozzle or pipe for 1 and 4 furthest away from the breather?

Good thread, keep it coming.

Yes, I've heard that but haven't experimented with a jet-size richer on the inboard cylinders due to greater heat. But it does sound like a good idea. I don't know if the blow-by is a significant factor in jetting. If so, I would think very little, just adding a little extra HC.

OK. Here's my question.

If a system like I'm showing you were an option to buy with a set of PODs, or as an add-on with some drilling and cutting involved, would you pay an extra $50 or $60?

Me, no, I'm a stainless steel fetishist. SMC on zinc plated wouldn't work for me.

Get some Stainless fittings and make a few up and test market them on ebay I'll buy a set.

It's just a prototype. I got most of the stuff at Home Depot. And if you take a look at my bike it's pretty concealed, not even noticeable unless you pointed it out. Really want to know if riders like yourself would appreciate what it does -- cosmetics is secondary. If produced the whole thing may be straight black plastic and rubber.