Something doesn't sound right, you shouldn't be having to drop down "a lot of gears" to overtake cars, maybe you have a European import with a restrictor kit fitted? You'll need to take one of the carb tops off to see if you can find a grommet that would prevent the slide from fully working. You could maybe check the Throttle Position Sensor to see if this is out, check Pat's guide for details on how to do this, there is a link in the FAQ. Might also be worth running some Redline fuel system cleaner through a couple of tanks in case the carbs are slightly blocked.
An ignition advancer will give you a slight boost at the bottom to mid range but it's a subtle difference not night and day. You can fit one before or after Ivanising it will still have the same affect.
An ignition advancer will give you a slight boost at the bottom to mid range but it's a subtle difference not night and day. You can fit one before or after Ivanising it will still have the same affect.