[Ram Jet]

Originally Posted by Mohawk

Every engine has an ideal stack length for maximum torque=power at X rpm. Shorter stacks move power up the rpm range & longer ones move it down. You need to tune the intake pulse for your required use. This can be done with intake length & exhaust primary length.

The Ninja 300 & Versys-X 300, share the same engine, but the versys makes more torque lower in the rpm range & overall but loses out on max hp to the ninja. All achieved with intake & exhaust header lengths.

For maximum power you need an airbox & velocity stacks, plus ramair if you can get it. My 800 gained 5hp with no other mods other than moving the same filter to the top of the airbox, rather than sandwiched in the middle, so the volume never changed, but the still air area above the v-stacks doubled !!! 5hp from just moving the filter location ! You need as big an airbox as possible after the filter. Minimum size should be 10x the engine capacity, there do not appear to be any gains past 20x which is usually very hard to package on a bike. So a 250cc would need 2.5L minimum & 5L maximum. Obviously the larger the engine the harder it is to package the larger airbox.

YMMV

Great perspective. Velocity stake length may be a-bit more complicated than you have described as cam timing and valve overlap are big players too. I have a Honda FT500 single and have kept the airbox intact. It's a wonderful design but the airbox takes up about as much space as the engine itself. The airbox on the Ninja and my Honda serve a multitude of purposes and I'll admit it's tempting to free-up a-lot of internal frame space but I think it's unwise to remove it. Don't anybody get mad. I'm just vomiting my opinion. I tend to trust Kawasaki engineers and if there was not a good reason for the design it probably wouldn't be there.

Bill