It turned out to be that for some reason i was hitting overboost and the ecu was going into protection mode and dumping fuel in. It was between sessions at sandown when i regapped the plugs and also reduced duty cycle on the boost control. Didn't want to take any chances and ruin another session. I've been too lazy to increase the gaps again, next plug change i suppose.
Yep, good old DT. Most panel shops wouldn't know what over fenders are and would be hesitant about repairing other peoples stuff ups, DT knew exactly what was going on just by glancing at the car and exactly what was needed to be done. My car had been painted by another shop around 10 years ago, the paint work was pretty good but the bodywork prep was not so good. Particularly around the rear quarters, you could see sanding marks through the paint and there was also some shrinking as well as the finish being a bit rough. There was a fair bit of work involved to get it all repaired, all the rear glass was removed and then they went to town digging out the filler which revealed that the over fenders were only riveted in but not glued. They managed to get some glue underneath them where possible and then refinished everything. I'm quite happy with the way it turned out and relieved that the paint matching is pretty spot on, that was my biggest worry as its not a standard Nissan colour and has got a fair bit of metallic sparkle in it. I just had a look at it before in sunlight and looks pretty damn good.