With an HCI combo what do you do with your timing and a/f ratio when adding say a 125shot. I would GUESS retarding a few degrees and then try to run just a little rich. Is this correct for as far as STARTING to tune a nitrous motor?
As a general rule, I think you want to pull out 2 deg. of timing for every 50hp of nitrous. So for a 125 shot you would want to pull out around 5 deg. It's also a good idea to go to the next heat range colder spark plug. You also may want to close up your plug gap to prevent the spark from being blown out. If you have an adjustable fuel pressure reg., a couple extra lbs of fuel pressure will give you an added margin of safety. Best bet is to get it on a dyno and make sure the A/F ratio is safe, say around 12:1 or even a little less