Pod Air Filters

The air is pretty calm behind the engine and carbs. Most carbs are designed to pull this outside air i keep talking about from that area OR the airbox.

I maintain that the carbs need a steady "high pressure" air to compare the vaccuum in the carbs to. A vacuum is only in comparison to some higher pressure. I understand how a venturi works and why it creates the low pressure vacuum that moves the slide. But a vacuum compared to what? To the original air entering the carb body. Which is directed to other parts of the carb through that small opening at the top of the carb throat.

Carbs can also be designed to take that air from other carb openings that don't go to the airbox, but designers have mostly gone for the "from the airbox" design to eliminate contaminates. Those carbs that did, would collect that air from a tube that ran up under the seat, or sometimes just in the general carb area.

I think we're all in agreement that the smaller surface area, and internal volume of the pods creates turbulence which is ultimately what we seem to agree on, as causing issues.

In the airbox, I would imagine the shock wave effect, if anything, is dissipated pretty quickly through the air in the airbox and dampened by free flow through the filter and box opening.

 

Ok permissiontolandfmx I'll come back to the pod party...but just because you asked and also because the request was made for 'tried it and here's what worked.'

I put pods on my brother's '73 CB350. It was seriously lacking in 'get up' and he dragged me into his evil plot for power. We used two 3" tapered pods and if I remember correctly (been 4 years) we took it from #60 to #70 on the primary and from #115 to #120 on the secondary(fast jet), those old Honda carbs are a bit different-air jets the same and originally no exhaust mod.

It already ran a bit rich before the pods and at first (before the re-jet) it went to very lean and had two major holes in the throttle response, very low and mid range. After the re-jet, and a serious effort to make his bores smooth as silk it was much better, also we drilled a few holes in his baffles. My brother was satisfied as the top end was much improved, but I noticed it still had hesitation off idle up to midrange. I told him it needed some kind of intake chamber/tube to smooth out the air charge, but he was happy so the experiment was over.

I would call this a pod success (90% good) but of course much smaller cc, unique old carbs, and only a twin. The pods had equivalent air and were far enough apart to not compete for flow. This is precisely why after I considered pods for my XJ and was told "don't do it," then I did the physics analysis (I know who cares) that I decided it was a "no go." And not to hit you with 'theory' again but the 4 pods lined up in a row and fighting for equal flow is why the problems exist in my opinion. After all the two outside (quiet air or not, thinking not so quiet) still have no competition on their outside 180 degrees, while the two inside pods are competing in 360 degrees for flow. Hence they will never be 'equal' with that physical arrangement. Ok no more theorizing.

That being said I still think it is possible to make them work, because with enough effort and ingenuity anything is possible. But I don't think anyone will ever just slap 4 pods on an XJ's carbs, with no chamber to smooth or equalize the flow and EVER get it to be fully balanced and functional like it should be. Sure you can tweak the fuel mix all day long and get it 'close' and after all that effort your gonna tell yourself "I did it!" But there is a flat spot in that throttle response and two are pulling harder than two others are for sure.

I am not an engineer nor am I a FD expert, but always willing to learn and if anyone can invent, test, and show a way to do this on a 4CV bike then by all means do it. Smoke them pods!!

 

http://autospeed.com.au/cms/article.html?&A=107749

 

Thanks for that link...

skillet

 

That is a great link. Yamaha did built Ford Taurus SHO motors that used a servo controlled door that switched from a short intake runner to a long one depending on RPM. In stock (from Yamaha) they were 300 HP from a 3.0 L V6 although Ford detuned them to 220HP. When the servo opened it was very noticeable and off the line they would ignite tires.