So last summer i switched my shot to 125. It worked fine the night i tested it on the track but a couple months later it isn't working fine. When I hit the nos it works until I am right about to shift at a safe rpm (not waiting till it gets too high) and then it makes a knocking sound almost like a misfire. After becoming aware of this I replaced the spark plugs and made sure they were the right ones. I also replaced the fuel filter, changed the oil and checked the nitrous line and was sure to add 91 octane. Everything seems to be running fine but the nos is still backfiring or whatever. Does anyone have any ideas of what it could be? If anyone could please help I really want to get it on the track this summer. Thank You

 

Is your car tuned for the nitrous? With a 125 shot it most definitely should be.

 

You say just before you shift,your fuel pump could be at its max. Check it out, get on a dyno tuner before you have a big problem.
muzzy

 

Well if changing the oil didn't work, I'm not sure what will.