Pod Filter Alternative?

[jcasey007]

Hi All

I've been working on an alternative to the aftermarket Pod Filter for my 650 bobber.

here's what I have come up with, this is the Mk1 version, I'm working on the Mk2 now which will have a black grill and copper end plates. I use a foam filter media which is specifically for petrol engines that I was able to cut down to size. I had the 3 pieces laser cut from my drawings.
the carb boots came off the Pod filters.







cheers

Jim

[cb in alaska]

Dude that is bad Ass, you tried it out yet? Does it work on cv carbs? What's your asking price or what does it take to build?

[jcasey007]

Works a treat, too early to say if better than pods but looks better, the total cost was £75 which is because it's solid copper, stainless or mild is about half that.

Re CV carbs, it is a matter of checking the carb spacing centres, I think they are different but if you want I can post the drawings so you can check

Cheers

Jim

[Folsoml]

Re CV carbs, it is a matter of checking the carb spacing centres, I think they are different but if you want I can post the drawings so you can check

Cheers

Jim

Sadly, it is more complicated than that. The cv carbs are not pod friendly in the least. I don't know if your invention--which looks cool, btw--will give the proper amount of still air the finicky cv carbs need.

[jcasey007]

You may be correct, I've never played with CV carbs

What does the inside of a standard air box look like? Anybody got a picture?

[Folsoml]

This is the best explanation of the problem with pods that I've seen.

An airbox serves many purposes and one of the most important is to supply the carbs with a consistent and steady reserve of STILL air. Under most conditions, pod filters can't offer this; they are affected by turbulence from several sources, including cross winds, the rider's body, and the bike itself . Air pressure is directly related to air speed and carbs have a hard time dealing with the constantly varying vacuum pressures that pods often cause. This varying air speed problem occurs on even a single-cylinder bike; the problem only increases on multi-cylinder bikes. Each pod is essentially its own air supply system; with potentially varying air speeds (hence varying vacuum pressure); at each pod (due to varying turbulence levels), you will have an issue that mimics that which occurs when one or more of your carb intakes has a vacuum leak: erratic idling, stumbling, surging, etc.

This is one of the reasons that a lot of pod-equipped bikes suffer from surging problems; even after re-jetting, the lack of consistent vaccum pressure causes fuel flow to ebb and flow.

We haven't even touched on the problems of pods while riding in rainy weather...

In summary, in certain situations pods can be beneficial but overall, for street riding, they cause more problems than they cure. Pods look cool, they make carb removal and install much easier, but they are inferior to a well-designed air box. The manufacturers in the 70s and 80s weren't stupid, their marketing departments knew even back then that people loved the look of pods and if they could have fitted the bikes with pods without adversely affecting performance and ridability, they would have; they didn't because an airbox serves several important roles that pods can never handle.

[MiGhost]

JC. The air filter looks real good. Very much like the old breadbox style. The only change that I would make would be to use a set of stock airbox boots in place of the pod boots.

It is not so much the airbox style that is the problem using pods with the cv carbs. The big problem is how the airflow enters the carb.
As Mainerider pointed out. It is the turbulance that is created that causes the problems.

The pods have a sharp turn into the carb into the boot, and very short throat length. This creates turbulance in the airflow right at the front of the carb opening where the air jets are. This causes the problem of the jets not getting the proper air supply. Which in turn creates the lean mixture condition.

With the stock airbox boots. The bell mouth design smooths out and, moves this turbulance away from the air jets to allow the airflow to be directed into the air jets for the proper mixtures.

If you look at it like this. You will understand it better.

Airflow can not turn at an angle. It will always try to go straight.
The vacuum created when the valves open, and the air/fuel mixture charge is drawn into the cylinder creates a pulse that travels back through the carb to pull more air in.

With the pods. This creates a rolling action to the airflow.
The airflow can not make the sharp turn, but the vacuum pulse pulls the airflow on a curve into the boot. This curved flow pattern creates a low presure (vacuum) area underneath it that the airflow spins back into, and slows down. When the airflow comes back in contact with the incoming air. It once again has to change direction, and speed up. This creates tiny vortexes (vortices') of swirling, spinning air (turbulance) that travel through the boot to the front of the carb.
When these vortices' reach the area of the air jets. They are moving in a direction across the top of the air jets. Not straight into the opening of the jet. This creates yet another tiny low pressure area right at the opening of the air jet. The short length of the boot does not allow the time needed for the airflow to straighten, and smooth out.

With the stock airbox boots.
The bell mouth (velocity stack) shape of the opening reduces the amount of low pressure area that can develop. This allows the vacuum pulse to straighten out the airflow quicker, and move it faster through the boot. As the airflow is not having to deal with the spinning turbulance. It travels straight into the air jet opening. Which is what you need for proper fuel jet operation.

Have you ever noticed how high performace engines running without an air filter almost always use a long bell shaped velocity stack?
To control the airflow, and limit the turbulance is why.

Sorry about the long winded, overly simplified, highly untechnical expalination.
Hope it helps to understand the problem with pods.

Ghost

[jcasey007]

Ok so that make sense, I can accommodate the standard boots within the design, searching CSM, it looks like you cannot buy them separately from the airbox (at £150), these are on ebay at the moment only in the US.





I will search UK sources for a couple of weeks to see if I can find some, failing that I am in Washington DC in 3 weeks

cheers

Jim

[cb in alaska]

Yeah if you could message me the prints on how to make this it would be greatly appreciated! If this won't work for you or you need some sort of compensation I'm sure we could work something out as well. I'm beyond stoked to do something like this on my bike

[jcasey007]

Happy to share, I've PM'd you my email address so I can send you the AutoCAD files but here are the jpegs as well







cheers

Jim

[jcasey007]

one more picture as I got the URL wrong

[JorgenL]

Nice progress!

As for the bellmouth thing of the boots, I'm with you.
When I run my carbs "naked" with no filter at all. It runs like crap. Jumpy idle. Bogging. Just plain weird.

When I put on my velocity stacks, without any mesh screens, everyting is smooting out. Rock solid idle, VERY good throttle response.

The only difference is the added length of the runners and the rounded edge. Many pod filters just slide over the carb and don't even out the edge between the carb and boot. The stacks smooth out perfectly. When you push a finger into the velocity stack you can hardly feel the joint to the carb. If I remember correctly the stock boots are also flush with the carb intake.

When I had my pods I made sure the boot ID was the same as the carb ID. I then glued a big hose on top of the carb boot and put that over my carbs. That way the transition from boot to carb was minimal.
I later scrapped the pods only because of aesthetics.

[aletstrejo]

can you send me the CADs please? im planning to do it next week, hope you can answer!
aletstrejo@gmail.com

[jcasey007]

I've posted them in a drop box for you or anyone to access along with all the other pictures etc.

viewtopic.php?f=4&t=14113

[Hutch1]

Based on everything I've read, I'm convinced the air box is a necessity unless you are a carb whisperer. That said, has anyone tried mounting a pod or oval shaped filter to the air box and eliminating the air cleaner housing? I think this would be a happy medium between pods and all stock for those who are concerned with aesthetics, as well as freeing up some additional real estate. I want to explore this route but have to sort out which filter to use (still may adapt the stock air filter), and also determine how best to mount the filter only to the air box.