After reading about a lot of guys removing the flapper valve, I thought I'd add my 2 cents.
What the flapper valve does is restrict the opening of the air intake below 3000-4000 R.P.M. The reason this is done is for better torque.
It works like this. When the engine is turning slowly it takes in less air. If the air intake opening were big, the engine lazily sucks the air into the cyliders. By restricting the opening size in the airbox, at low R.P.M.s it forces the air to move more quickly to get into the cylinders. This increased air velocity will actually act to pack more air into the cylinders.
When the R.P.M.'s climb, the valve opens to allow a greater amount of air through to keep the velocity and air packing going.
By removing the flapper, you actually allow for less air to get into the cylinders at low R.P.M. and you actually loose power.
It may actually feel faster, but that's because the power is reduced at the low R.P.M.'s so when the speed increases so does the power curve more drastically. Removing the valve actually makes the power curve steeper and hurts drivability and response.
Also, removing the flapper valve will change the airflow to the motor so the stock fuel map, or any maps from Yoshi or PC will not work correctly.
If you remove the valve, you actually need to get an ECM just so you can go spend a lot of money on a Dyno tune to get most of the performance back.
Hope I didn't rain on anyone's parade.
BTW, if you did see a horsepower increase on the Dyno, it's because of the tune-up, not the airbox mod.
I will make the following statement however, if you are going to use your Busa for RACE ONLY purposes and only care about peak horsepower, then rip the whole damn airbox out and set it up properly for racing. then you'll get that increase you're looking for. just remember, you're throwing out low end performance for more on top. Not my first choice for street use.
Johncal
What the flapper valve does is restrict the opening of the air intake below 3000-4000 R.P.M. The reason this is done is for better torque.
It works like this. When the engine is turning slowly it takes in less air. If the air intake opening were big, the engine lazily sucks the air into the cyliders. By restricting the opening size in the airbox, at low R.P.M.s it forces the air to move more quickly to get into the cylinders. This increased air velocity will actually act to pack more air into the cylinders.
When the R.P.M.'s climb, the valve opens to allow a greater amount of air through to keep the velocity and air packing going.
By removing the flapper, you actually allow for less air to get into the cylinders at low R.P.M. and you actually loose power.
It may actually feel faster, but that's because the power is reduced at the low R.P.M.'s so when the speed increases so does the power curve more drastically. Removing the valve actually makes the power curve steeper and hurts drivability and response.
Also, removing the flapper valve will change the airflow to the motor so the stock fuel map, or any maps from Yoshi or PC will not work correctly.
If you remove the valve, you actually need to get an ECM just so you can go spend a lot of money on a Dyno tune to get most of the performance back.
Hope I didn't rain on anyone's parade.
BTW, if you did see a horsepower increase on the Dyno, it's because of the tune-up, not the airbox mod.
I will make the following statement however, if you are going to use your Busa for RACE ONLY purposes and only care about peak horsepower, then rip the whole damn airbox out and set it up properly for racing. then you'll get that increase you're looking for. just remember, you're throwing out low end performance for more on top. Not my first choice for street use.
Johncal