The first thing i did to my car 2 months ago when i got it was replace the torn rev c diverter valve with a rev d item. Since replacing it i have got more power at higher revs but there is more hissing when loading the engine up at low revs. Basically it sounds like its a bit of a duff item, unless i have a leak elsewhere but ive had a look and cant find anything. Is it worth me getting a rev g diverter valve and fitting it? Is it known that the revision d's are a bit crappy or come already faulty? cheers