Topic: Pod shape's effect on performance?

[calj737]

So, Ive got 4 K&N conical pods on my bike ('74 550) with a MotoGP exhaust. Im having the bike tuned on a dyno by a local shop, and the first comment out of their mouth was "You'll want to change those pods to oval units for better airflow".

I'm certainly no expert, but I am reasonably intelligent; yet I fail to understand the relevance of the pod shape to the flow characteristics, especially given their location (facing rearward) and exposed (no air box). If the height of the pods (regardless of the shape) is equal, then I see no surface area difference for flow. In fact, the separation of the units "should" allow more free-flowing air around the circumference of the pod, no?

I need input from those more knowledgeable than me on this topic. If their (bike shop) logic stands to reason, should it be a single oval spanning 4 carbs, 2 ovals spanning a pair each, or 4 individual pods?

Maybe TwoTired and Hondaman will pipe in with their infinite wisdom and knowledge....?

[Powderman]

I think you will find the separate oval filters are taller than the round pod filter and the same width so they will flow more air. If a dyne shop made that recommendation I would imagine it was through extensive results from past motor runs. I'm beginning to think K&N is not the end all be all in filters. They do have the advantage of better design of the internal velocity stack but they are still a compromise of filtering and air restriction. They flow more air but at the expense of filtering dirt. The oil helps collect dirt so it can have bigger openings to flow air.

[calj737]

They have to cut the oval filter down to the same height as the cone to clear the frame. So, with that, they are the same height.

I agree with the premise of dyno results should equal better advice, but I also believe anecdotal advice is not the same as empirical evidence.

[lone*X]

The biggest question is Are You happy with the way it is running?  Does it pull smoothly throughout the rpm range?  Or do you have flat spots in power delivery at a particular rpm?  Do you really need to make more changes?  Is a very small improvement in flow necessary at this time?  Its not going to buy you a lot of HP or torque with that change only.   If you have done you homework, you already know what the forums consensus is on pods vs stock air box.   Hopefully the shop made a recommendation on the basis of trying to get the most flow from the filters and the most improvement in power delivery but some shops will make recommendations that will only improve their bottom line with additional pulls and tuning sessions.  Will they guarantee a noticeable improvement in the performance if you go to the expense of changing filters and paying for another dyno session?

And if they made this oval filter recommendation, wouldn't they be the ones to answer your questions about the filter design, numbers,  and maybe a recommended source?

[wowbagger]

I think, by taller, powderman means the vertical height of the oval when mounted on the carbs, not the horizontal height from cap to mount ring.

That said, geometrically, the cone would have a taller wall than a cylinder or oval.....so, I've got no help to offer this conversation

[lone*X]

One other thought.  is the MotoGP running open or baffled?  Not enough back pressure can play havoc with jetting and air flow. 

[750cafe]

The larger oval design offers more surface area but the cone shape offers more readily accessible surface area between the filters in my honest assessment.
I have several bikes with both styles on them and do not notice an appreciable difference.
For the most heavily modified bikes that I own, I use the cones. 

Eric