Ram Air Inlets

Different model variants, such as the 668, have a form of ram air induction with tubes from scoops in the front fairing assisting breathing at higher speeds.  These tubes are made of concertina tubing, and it has been suggested that replacing them with ones made from something with smoother walls will aid top end performance.  The tubes do, however, by their nature, reduce effective inlet area to that of their entry tubes into the airbox.


The standard airbox on the 668 is regarded as being very restrictive.  The same airbox, complete with provision for the ram air tubing, was used in all models, even those without the ram air scoops, thereby potentially constricting induction.

An option is drilling one or more holes in the standard air box in front of the air filter.  A single hole three inches or more in diameter has been suggested.  Another option is discarding the front section of the airbox and replacing it with a frame, perhaps made of wood, to hold the air filter by the standard retaining clips.  You could also replace the standard paper element filter with a more free flowing reusable filter such as the K&N. 

More radical is to remove the airbox completely and fit pod filters to specially designed inlet tracts.  This will also likely mean repositioning of some of the EFI sensors.

Inlet Tracts and Manifolds

The standard inlet tracts are possibly a bit restrictive and could benefit from some reshaping.  There is a discussion of this in the extreme engine mods section, although there are potentially improvements to be had from less extreme improvements.  This sort of thing is best left to professional engine developers, equipped with flow benches and the appropriate tools and experience.


In every case where you make changes to the induction system you should remember to retune the engine on a decent gas analysis system.  Improving the flow of air into the motor will mean that the engine will run lean and hence hotter unless it is retuned.  This is most definitely not a good thing!


© Steve Carr, 2001-2007

Site created February, 2000.  Last modified Friday, May 15, 2009

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Last updated
30 May 2005