i know this sounds crazy but your vtec is set entirly to low, when vtec is set right you should not feel it engage at all,
what is happening is when the car switchs cam lobes your actually losing torque and horsepower at 4000 rpms because the cam profile isnt desined to make power at that rpm
the optimum vtec setting for a stock camed d motor is between 5300 - 5800, while for a more or less stock internal b18c1 the optimum vtec is between 4300 and 4600, i know this from HOURS of dyno exprenice
i wish i could put a dyno plot on here and explain my self but i dont have any, vtec engagement is the quickest fastest and easiest thing to tune on a dyno and for a stock compression naturally aspritated honda is the only computer modifications you can do to gain any real et on a race track, changing the af ratio and igntion timing in the computer will just hinder a car at your level now.
think of it as walking up 3 hills all the same height, the first is a slight slope then at one point the slope goes up real fast (vtec too early) the second you walk the same slight slope then you have to go down hill for a little while then sharp back up hill (vtec to late) the third you have a smooth consistent climb up the hill, remember all 3 reach the same point but which one is the least work to get there.
sorry for correcting you in your intro, doesnt mean i dont like just means im willing to help, if you have any questions just ask
edit ps leave it running rich when you first get the nitrous and learn to read you spark plugs, if you rich you wont hurt anything if you lean you melt plugs then blow headgaskets then you turn out with a block that looks like this