i have a 355 that every so often has some run on.the timing is @ 34* and everything else works great.it has the performer package but with world angle plug heads that need shorty plugs for 2 cylanders.it also gets a 150 shot of nos from time to time.now i think the term is called deaseling from to hot of a plug.does anyone have a idea what heat range i need to be to make this annoyance go away?
                        thanks,Darren  

Are you sure diesel problem (engine running after shutoff)in your engine is due wrong spark plug heat range?Usually this problem occur due excessive compression ratio,engine with high water temperature,hot spots in cilinder head due sharp points or carbon buildup.
If your only problem is diesel efect (no pre ignition with pingin)you can use a cut of solenoide like GM use to install in some quadrajet in the 70s 80s.  

I dont believe it could be from high comp. it just has regular flat top pistons with the valve reliefs and stock felpro head gaskets.To be honest it dont know what the compression ratio is but i dont think it would be more than stock.The temperature is pretty consistant at 170-180.I dont know about the carbon build-up,that might be a possibility but wouldn't a couple shots of nitrous at the track blow that out?I also know it should run a cooler spark plug when spraying.Right now it has R45T but im not sure what number would be a cooler plug.  

Try pulling your timing back from 34* to 32* or even 30* degress total timing. Also, go to any NAPA store with your plug # and tell them you need 1 or 2 heat ranges cooler. I believe it is R43T in AC Delco. Make sure your balancer is marking corectly. If it has slipped you could be way of on your timing. GOOD LUCK.