If this is for a racing Vincent.....How far do you think you need to go.? The NASCAR engines you talk of most likely rev to 9500 rpm or more.....Even the all out efforts that the Irving Vincent bikes are built to rev to about 7500 max And they put out about 145 HP from 1300 cc 2 valve engines. All the development work you talk of, perhaps you should talk to the Horner brothers who developed the Irving Vincent. The initial design work that was carried out on the heads that Terry sells was from John Trease....He is an out and out Harley man, and his period 3 59' sportster engine (featherbed frame) racer is in my mind the fastest road racing Harley in the world......It is his knowledge of racing and building high output Harley engines, and this is what went into The Vinton racer I mentioned earlier. Much of this work John told me he would likely never repeat, as it was just too time consuming. The bike was very competitive, although some weight changes would help, but the new generation of Manx's has changed the goal post a bit. The ratio you need to give 0.500" lift at the valve is 1:1.15 This from the 0.433 or 11 mm travel already. The other reason I need to make my own valves is because the inlets are 0.125" larger than standard. You generally need to remember the travel ratio of the rocker as well, this at the valve, which is one third up to two thirds down.....from the center line horizontally through the rocker and at right angles to the valve from the vertical.
