What is the correct overall system length?
Induction length is one of the most important aspects of fuelling performance engines. In our experience an under-length system is the greatest cause of disapointment, with loss of up to 1/3 of power potential. There are a number of good books on the subject and the serious developer is referred to these and, in particular, dyno trials. A guide figure, from the face of the trumpet to the centre of the valve head is 350mm for a 9,000 RPM engine. Other RPM are proportional, i.e. for 18,000 RPM the figure is ca 175mm. Any air feed system to an airbox or filter can have a large effect on the power curve and must be considered carefully – particularly if the airbox is small. The induction system is part of a resonant whole – from air inlet or trumpet to exhaust outlet – and the ideal length is heavily influenced by the other components.
