There is a lot of "not so trues" in this post.
(1) 150hp as far as what is recomended as a baseline tuneup for the nitrous manufacturer will not net the same horsepower gain from one engine to the next, so a 150 shot on a 10.5-1 350ci will not net as much horsepower as a 150 shot on a 15.5-1 632, both tuned accordingly. There is not one nitrous system manufacturer out there who can recomend a tuneup that will be perfect out of the box. The only way to give a nitrous engine what it wants or needs is the ability to read spark plugs and make the proper adjustments to get the mixture right (nitrous fuel ratio) and ignited at the proper time (heat mark on ground strap of spark plug)
(2) Retarding the timing does not reduce the horsepower by 10hp per degree, at least not while the nitrous is in use. Retarding the timing allows the mixture to ignite at the proper time so that it doesnt detonate or pre ignite, which causes serious harm to an engine.
(3) Just to say to pull 6 degrees of timing for a 150 shot is wrong also, one needs to know what the initial timing on the particular engine being tuned is first, then there is the question of what the valve angle is on the heads, type of fuel being used, compression ratio, cam info....etc.
A properly tuned nitrous engine will leave a clean plug with the timing mark just around the bend on the ground strap of the plug.
In my particular engine when I go down the track with both foggers blazing, my timing is pulled down to 8 degrees. :shock:
Not trying to step on anyones toes here, just wanting to share some of the things that really matter when tuning a nitrous engine.