View Single Post
Old February 17th, 2011, 01:00 PM   #39
VeX
That's me!
 
VeX's Avatar
 
Name: TJ
Location: Ames, IA
Join Date: Nov 2008

Motorcycle(s): 2008 Ninja 250r (Tis blue), 2008 CBR600RR

Posts: 454
Quote:
Originally Posted by afbarr View Post
So did a consensus emerge on whether it was better to remove or keep the oem airbox runners when removing the airbox and replacing with a standalone air filter (such as the k&n r0990)?

And is anybody aware of and can recommend a book that covers the topic at an "educated layman's" level or deeper? I looked online but the "articles" are rather brief on the topic.
The general idea of tuning your intake runner length isn't terribly complicated. To effectively do it you have to actually know a couple of variables (which involves some math ).

The airbox on the Too-Fiddies is terribly restrictive and it's done this way to create a pulse wave in the airbox. At low RPM's you get a slight bit of pressure in front of the carburetors so you can get more laminar airlow at low RPM's. At high RPM's the effect is lost and you're left with a restrictive ass airbox.

So by removing the airbox you actually lose a bit of torque at low RPM's. Back to runners:

Intake runners act like a shotgun to smooth airflow. Like most things on an engine it's a two edged sword. If you have small diameter runners and they are long airflow through will become super laminar (smooth) and you will get more air/fuel into that particular cylinder. What happens at high RPM's though? At high RPM's it's like sucking soda through a coffee stir stick. The soda will come out at a high velocity, but not a lot of it (and you have to really suck to get soda through.

Using larger diameter and/or shorter runners will allow for a ton of flow through and at high RPM's airflow will be relatively laminar, but at low RPM's air is going to be super turbulent. By keeping the intake snorkels IN the air filter you increase your runner length which helps smooth the airflow. So you regain some of your lost power at low RPMs.

There are various clever examples of getting the best of both world with intake runners. The new R1's for instance have runners which are telescoping. So at low RPM's the runners are long and at high RPM's they shorten. Pretty cool concept.

So yeah, as for the double edged sword: What are you trying to do? Racer X needs maximum horsepower (so high RPM) and hence would need a large diameter or short intake runner. If you want a little more "umpff" getting out of the hole for stop-light to stop-light riding, you might extend your runners.
VeX is offline   Reply With Quote