I think that's an interesting area too but using laptimes from the two Nats solely to analyse the effects of more minor mods is difficult.

The two events were over a year apart and in that time all drivers have had more experience with their car, either at track days or just driving hard generally. A number of guys were faster than last year and yet had done nothing major to their cars inbetween (jormatom is a good example).

I reckon experience was probably the biggest factor in the improved times of the non-turbo owners, unless semi-slicks were used (worth 2 secs per lap in Len's view).

As somebody who struggled to recollect the difference in my car's track performance before and after suspension mods (when the track attendances were nearly a year apart), I think the best way to assess these more subtle mods is to do some back to back testing on the same day using the same driver in different cars (preferably using a stock car as the control). Alternatively, driving the same car shortly before and shortly after fitting the mod (i.e. within a month or so).

This is why I was particularly keen to get Rod out in my car to get his views. We ran out of time for that because he was busy instructing others (and trying to get his own times down) but we have loosely talked about attending Wakefield again sooner rather than later to do some testing (i.e. similar to the tyre testing Rod and Len did last year).