Well finally got the car down to my local rolling road - Mikeanics in Congleton - to see if that
exhaust manifold managed to unlock the DTH 48's that never really delivered as much as I hoped. My engine man said that 48's gave more power on the dyno than 45's, on similar spec engines, so I was hoping for an increase when we fitted them. As I said, this increase never really materialised and the verdict at the time was that the
exhaust manifold was probably now the restriction. So this is what prompted the new manifold described earlier in the thread.
So down to the rollers and the map needed changing quite a bit. Promising start....
I am staggered by the result. There was not much increase in peak power (4hp) but the midrange has been massively increased - by as much as 30hp at 5500rpm!
Power increases shown below.
Absolutely bang on, well chuffed.

Exactly what I was hoping for.
Ave it
Rob