im looking for a formula on how big to make my air intake connecting to my air box...

each carb including the throttle plate area @ WOT is 38mm, the total area of all four is 45.34 sq cm. the total area of the stock intake pipes is 39.25 sq cm. Should i match size of that carbs? go bigger? is there an approx formula? for all of you that don't know the entire intake system on the 99' 900RR is made pretty bad. i was going to buy the APK kit from factory pro which is suposto make around 4hp on a stock motor. and all that does is cut out the insides of the air box and convert from a super tiny plate filter to 2 cylindrical filters. the 2 runners coming out of the air box go to a tiny scoop thats about 1.5" wide and 1/2" tall which is poorly made as well. im going to convert it to ram air, which (correct me if im wrong) i know doesn't work the best on a carb bike but i know will make much more power compared to stock. Ive almost finished my designs on a carbon fiber oval tube going from the box all the way to the front. i was going to kinda copy the one on the GSVR

the only difference is that the middle of the front wont be arched up as far. only enough to clear the front fender and match the arch of it. if the apk gets 4hp then im hoping i can get 5 out of it.

how big should i make it???

 

From what I've learned, intake velocity matters a lot. Blowing out with your mouth is a good example. Instead of sucking in and imitating a intake system its easier to gauge the velocity of air when you blow out. Open your mouth wide and blow as hard as you can. Not much pressure is created. Make a small 'o' and blow like you're blowing out some candles. The pressure is much greater.

Ofcourse, too much velocity but not enough supply (small opening) will starve the combustion chamber. I think its usually a science left up to flow bench artists. Plus more air means you'll need more fuel. Usually something that needs to be dyno tuned.

Here's a calculator.
http://www.btinternet.com/~mez....html