I wouldn't go above 150ish with nitrous. Why the timing problems? What ECM are you using? I have EFI, have done EFI on many, many combos, only one ever gave me problems, it was just the plug wire/ non resistor plug combo...... I run non-resistor plugs all the time, no problem. Those plugs may be too hot. With EFI you can certainly run a nice cold plug and have no problems with them.