Dr Jay's Tech Topic of the Month

Modifying your Airbox- Is it a good idea?

In the old days, Life was so much simpler. We had carburetors, and if we even had an air filter, it was usually just clamped to the back of the carburetor. Ah, the old days.....

Nowadays, everything is going Fuel Injected (FI) and boy do I love it! Fuel Injection is so much more accurate in anticipating the operating parameters of our engines, we always get the right power and efficiency at any throttle opening and load. With remapping modules available it seems even the backyard mechanic can play formula one technician and adjust his system until it is all messed up.

There is one modification that is a no-no that we are starting to see more and more of- people are modifying their airboxes on FI equipped engines and this can cause BIG problems. There is even someone out there who posted instructions on the internet on how he modified his airbox on his Vstar1300 and includes very specific instructions on how you too can be that dumb.

To better understand what an "Airbox" is, it is the large plastic "box" that houses the air filter on unmodified motorcycles. Despite this simple description, it is NOT a simple box. Air boxes are very carefully engineered for a number of reasons. First, the airbox quiets intake tract noise. Ever removed the air filter lid on your old V8 and held the throttle wide open? The intake roar is quite noticeable and can even overpower some rather loud exhaust systems. Second, the Airbox provides weatherproofing. It protects air filters from rain and water. Third, the airbox is designed to provide the correct amount of air flow to the intake tract, both in volume of air flow and in turbulence. Now, this is where we start to see the problems with FI equipped engines.

In the Automotive world there are many sensors providing data to the computer which then interprets this data and feeds the engine the correct amount of fuel. One of these automotive sensors is called a "mass air flow" sensor and measures the air flow coming out of the airbox (called an air filter housing on a car) and the computer uses this sensor to insure that the engine gets all the fuel it needs to supply that air flow number. So on a car, if you were to modify the airbox, the computer has a way to compensate.

On our Yamaha's, we do not have a mass air flow sensor. Instead the computer is calibrated to the STOCK airbox. Yamaha engineers know how much air can flow through the stock airbox and air filter and have "mapped" the ECU (Electronic Control Unit) to supply the correct amount of fuel for the throttle opening it sees. It is not rocket science to understand that if you modify the airbox on an FI equipped Yamaha, you are inviting a host of problems. On the lucky side, your engine will be too lean and misfire and/or backfire badly and on the not so lucky side, you will damage the engines pistons and valves. Because the ECU does not know that it is receiving more air than it is supposed to, the engine WILL BE too lean!

So, be a rocket scientist and do not modify your airbox on any FI equipped Yamaha or suffer the consequences. BTW, we still have a lot of engine parts available for late model FI Yamaha's and would be happy to quote you a top end rebuild......

Ride Safe- and SMART,

Dr. Jay