Follow this link for fitting and timing "Hot Road Cams"
I have been working with David Newman of David Newman Cams. He has 38 years of experience and is tooled up with hundreds of thousands of pounds worth of CAD/CAM CNC machinery. Jobs lying round the immaculate workshops include Vincent twins, Commando, Lotus and Cosworth. We have discussed the design of a Fast Road cam - increased performance, wide power band, maximum volumetric efficiency, retain the standard followers, although the follower blocks will need to be eased by about 1mm to allow for the extra lift.
talented amateurs like ourselves, the rule of thumb with cams is "one step
softer than you think". If you are Sheene or Hailwood then you will be able
to do better with the most radical cam. But then you also need a Mega, a big
bore carb that won't be civilised at low revs, a six speed box, stop drinking
and smoking, lose a stone, win the lottery or get factory sponsorship.
With full acknowledgement to Phil Irving and "Tuning For Speed" I reproduce one of his diagrams. Essentially it shows that the hot road cams below will be a source of additional performance over and above other tuning work.
The specification for standard and my hot cams is below.
|Model||In Opens BTDC||In Closes ABDC||Ex Opens BBDC||Ex Closes ATDC||Lift|
|Phil Irving Min Spec||35||60||65||30||???|
|Hot Road Cam||55||85||85||55||0.354"|
|79 x 100 Manx||60||67.5||85||45||???|
The data above shows that...
The ES2 standard cam is a little softer than the Model 19 cam.
Both of these are too soft in the opinion of Phil Irving.
The Hot Road Cam is hotter than the Phil Irving minimum spec.
The Long Stroke Manx cam is comparable
Top is the Standard ES2 Cam, below is the Hot Road Cam. The increased timing is evident, even though the increased lift is impossible to judge.
There has been some talk cautioning the comparison of ohc and pushrod cams due to the flat v radiused followers. In fact flat followers make the most of a cam profile; radiused followers reduce the acceleration of the valve train, but do not affect the overall timing. The effect of a radiused follower is to dilute slightly the sportiness of its cam.
I have received information that some ohc profiles had 0.500 lift. This information did not specify whether the lift was at the cam or valve. My rocker ratio, which is only slightly greater than standard, is 1:1.36. This means that my valve opening is 0.354 x 1.36 = 0.482 (minus any tappet clearance).
So far users of my Hot Road Cams have not needed to modify the cam follower clearances, but you need to check that the extra lift does not top out the followers. (See above link on fitting)
Lighten the rockers...they are doing less work but also need to move faster. These have also been trued up so that the surface that bears on the valve stem is exactly parallel to the axis of the rocker spindle. This means no sideways thrust. There is still the "wipe" effect but a 3/8ths end cap on the 1/4 valve stem mitigates to a certain extent.