there tends to be no flange at all on bike bodies, Colin's trumpets are tapered to fit just into the body, and you secure them in place with a grub screw.

got any pics?

A starting point for working out the length and diameter of intake runners can be gained from the following equations. In a Helmholtz Resonance system (one with runners connected to a common plenum), US-based engineering guru David Vizard suggests that a runner length of 17.8cm at 10,000 rpm makes a good starting point. (In this context, "runner length" refers to the distance from the inlet valve to the plenum chamber.) Add to this length 4.3cm for each 1000 rpm less that the system is being tuned for. Tuning for peak torque (not peak power) is the norm, and so if the engine were being tuned for 4000 rpm, a runner length of 43.6cm would be required. You can see that for an averagely-sized engine bay, the longer the runner that can be fitted in, the better!


One equation for runner diameter is to multiply the engine volume in litres by the engine's volumetric efficiency, then by the tuned rpm, then divide this sum by 3330. The final figure is square rooted, giving the runner diameter in inches. As an example, a 5 litre engine with an 80 per cent efficiency (expressed as 0.8) and tuned for 3000 rpm, will have a runner diameter of 1.9 inches, or 48 mm. The volume of the plenum should be around 80 per cent of the volume of the cylinders to which it is connected.

Do you have a contact email for either of those welshpug?

I will make a thread when its done lam6 as there are always loads of questions about using bike bodies and no concrete answers!