Newman Cams

[Charles P]

Thanks all, I have a stepped key on my current gear which allows for adjustment by half tooth. Depending on how it fitted I might have to try something more sophisticated, in which case I'll get in touch with Dave. Does he need the original outer part of the gear to start with?

Any thoughts on the profiles themselves? What is the max duration/lift you would live with on a car being used on the road? Not intending to do many hill starts but don't want to be burning the clutch out every few months!

Dave's are new steel gears. If it's a mag engine I'd replace the original gear - they do break.
I reckon 260 degrees will be fine in a lightweight road car and you probably don't want/need much over 270 lift. It really depends what you want the car to be. Until the development of variable valve timing technology camshafts were always an exercise in compromise. 
If you're worried about the clutch then fit cast iron linings (as per the works). Makes a very nice clutch, long lived and no nasty smell if you do slip it.  

Charles

My understanding is that extra lift beyond the point of maximum flow is still useful as it increases the amount of time the valve is open at the peak flow level.

What is the downside of extra lift? Is it just wear on the valve train and noise or are there other factors that I am missing?

The downside of high lifts is in the acceleration and subsequent loads imposed on the valve train. This can lead to increased noise, wear, risk of breakages and the need for stronger valve springs. Stronger valve springs waste power. Having lift above max flow would seem pointless to me because it's adding load without any apparent benefit.
The ideal cam would open the valve from closed to open almost instantaneously and hold it at maximum opening until it shuts like a trap. Clearly that would impose enormous forces on the drive train. Every other cam is a useful compromise between loadings and flow. A decent outfit like Newman will have done their maths to keep things in check and the three key measures are velocity, acceleration and jerk (yes, really - jerk is the derivative of acceleration). Whether Newman will share these figures I don't know but they are the standard way of comparing cams. I've never had a Newman cam to compare so can't help to measure an calculate

c