Intake system length

[phoenix]

Originally Posted by ian_w

They are only 'rules of thumb' and should give you a ballpark figure for sizing valves and ports. Equation I use is:

MGV = Stroke * RPM / 30000 * ( Bore / Diameter )^2

Where Diameter = Area of interest, i.e. valve or port.

As you say in this case, the 33mm valves reach 70m/s at around 8500 rpm. Above this speed they will probably start to restrict the engine so peak power may be closer to 8500 than the 9500 max rpm.

Where it is not possible to get exactly 70 and 100 m/s at the max rpm, I would have thought a good starting point is to maintain the 70/100 ratio between valve and port sizes.

Why do you prefer not to have the port max out at the same engine speed as the valve?

[Al Weyman]

Thanks Au and Gordon. I am thinking of fitting the stongest spring I can find for the 1.47valve pockets a K-Motion 800 http://store.summitracing.com/partde...part=KMO-K-800 as I am reluctant to take them out further (see thread with holed cylinderhead!) and sorry to hijack Dennis I'll shut up now. ;-)