Here is the best explanation as to why the factory airbox is better than individual pods.timwill730 wrote:A little update that I did last night. I ended up putting a jet kit and pods on the carburetor
Taken from the old forum here.
sportieboy wrote: Quote:
Because only one cylinder is pulling air at any one time, those dimensions would be pricisely adequate.
I don’t have the Seca’s camshaft specs on me, but let’s assume the intake valves open for 35 degrees. That’s probably close… The engine is a four stroke, therefore it cycles once every 720 degrees. With four cylinders, total intake for one complete cycle is only occurring for a total of 140 degrees out of the 720 degrees. In other words, the carbs are only flowing air roughly 20% of the time the engine is running. Plus, the firing order is spaced evenly around that 720 degree cycle – no overlap. So, there’s not only never a point where more than one carb is flowing, in fact there’s approximately 145 degrees of rotation between the time when one intake valve closes and it’s carb stops flowing before the next intake valve opens and it’s carb starts.
Therefore, as long as the intake to the airbox is at least as large as one carb, there is no restriction. The airbox horn can flow 100% of the time. In fact, I don’t remember the exact dimensions, but the Seca’s intake horn is a few mm larger than one carb – therefore it can flow more than one carb can ingest at any time. Plus, you’ll notice it’s not just a hole into the box – it’s a velocity stack…
I believe the total size of the air box is more important than the opening.
Jason is correct, the volume of the airbox is critical. (Read about any new sportbike and they’ll typically mention how much larger they’ve managed to make the airbox…) Velocities are high going through the carbs and when the intake valves close, it sends a reverberation wave back up through the carb. The larger the volume of airbox, the better it can cancel that wave, allowing the next reversal of air flow back into the carb (when the valve opens again 685 degrees later) to happen more quickly and smoothly.
Pod filters don’t have that advantage. In fact, air movement on their outside is turbulent, depending on the aerodynamics of the air flowing around the engine, the riders legs, etc. (Quite often it's a partial vacuum.) The air supply might be good, it might not – it’s impossible to control and it will vary depending on how fast the bike is moving. Airboxes eliminate all those variables, supplying the engine with a consistent source of air and making it easier to tune the engine for consistent operation at any speed.