if you have the DOHC neon engine then it is not a 420A...but is the same for the pourposes of turbocharging...as far as detonation goes, you are first off sure it is detonation correct? how did you come to this conclusion...detonation is generally not a problem unless you are running high boost, as for retarding the timing, forget it, you cant really touch it, the computer controls it, and short of a $300 ignition box, theres not much you can do about it, and if you spend $300 you might as well buy a MegaSquirt, but I for one doubt detonation is your problem, since there are a lot of people running high boost on the stock computer, more likely your issue is fuel, and/or MAP sensor cutout