[dbn04]

need a bit of help with a problem ,it seems the valve springs that came with the heads are weak and motor has a power dip at high revs (around 4500-4800 rpm) this shows up on a dyno , it also seems to have a flutter (only word i can think of) when you excelorate and back off a little . a couple of mechanics and the 2 dyno guys say its the valve springs. of course ford motorsport say they dont have problems with there springs and wont replace unless i prove which ones are failing , so my question for you folk out there is 1 : have any of you had probs with the same 2 : should i use another type of spring from someone else,.
any help would be appreciated .
darren