Hi, OK oh wise ones -what's the answer. 650 pantah engine, standard cams, cont 2-1, 36mm dellortos, which inlet trumpet and why? 45 48 or 70mm long (don't ever recall seeing a long trumpet on a pantah I must admit. Answers on a postcard to the usual address Keith mm
I have no idea. But in "Tuning for Speed" Ch13. p.141 Phil Irving says - "Various formula have been proposed for determining the best inlet length for maximum power, but it is a difficult matter because changes in cross-sectional area, such as a long intake bell-mouth, or any diversion from a plain straight pipe affect the result. In general, good results are obtained with a length of 90 in. divided by the rpm. in thousands which gives 15 in. for 6,000 and 13 in. for 7,000 r.p.m." I'll let you do the maths
Thanks Steve R, just the informed useful answer I needed. I shall buy some short dellorto trumpets. thanks again. Keith mm
Agreed. It's a useful book. I've had my copy for about 45 years and still refer to it now and again but as you say Steve, things have moved on. As I understand it, the inlet and exhaust are all part of tuned system so that changes made to any one part will have an effect on the whole. So the optimum inlet tract length will also depend to some extent on the exhaust.
