Alex, I have done an awefull lot of work in this area and it is from this that I have my own range of cams for RS turbos and cossies.

As a basic example if we utilise a turbine housing with a larger area/radius ratio, in order to combat an increase in lag and reduction in response, its essential to decrease overlap. This doesnt mean you necessarily have to reduce the cam duration but as with all factors everything has a knock on effect.

I'm not going to quote specific figures for obvious reasons, but lets take for example a cvh turbo.

I have a specifc cam profile I use when running a 0.48 exhaust housing. When I upsize this to a 0.63 I regrind the cam with an increase in lobe separation. (i.e. decreasing overlap)

This results in an engine which drives equally as well as the 0.48 with similar lag between gears. The difference then is simply a later spool up time with the 0.63 but of course you get a corresponding increase in top end power.

If I left the overlap the same the 0.63 exhaust housing simply would not work at all!!! The engine would literally take several seconds to come on boost when changing gear!!

It's a complex issue and the best way to develop a camshaft is by real experience on the road NOT on a dyno. A camshaft CANNOT be developed on a dyno as it does not give any driver "feel" feedback.