is it possible to use the largest nitrous jet and the smallest fuel jet for this kit to produce a larger than 150 shot safely?

 

I am assuming 150 is the largest gets that come with the 5151 kit and you want to use the smaller fuel jet to squeeze a little more power out of the system because they all come tuned rich for a safty factor from the manufactor.
Well if you go with the smallest fuel jet (for 75-100 hp for example) you will blow up you motor soon as you hit the button. I would use the 150 jets for fuel and nitrous and work with the bottle pressure (with bottle heater) or fuel pressure (with regulator) to fine tune you setup for more power. I would not do any of this though without a good O2 sensor and gauge to monitor your air fuel ratio.
I would also not buy larger fuel and nitrous jets than are supplied with the kit (to get more power) because the lines and solinoids could create a bottle neck in the system and you might not get the mixture you anticipated on with the larger jets. Your results could be a fried motor.
If you looking for more power out of you system you really should look into buying a kit that will suit your needs. Someone else may want to chime in because I am no expert on nitrous setups. I have just read alot about it and set my system up last summer, N2O is some fun stuff but do your homework!

 

If I lowered the fuel pressure via AFPR will it result in a little more power??? Right now it is at 51 psi with #24 injectors.

 

Yes that is the idea. But if you lean it out too much you smoke your motor. I would call NOS tech line and ask them for more specific information. Once again I would not try it without some kind of air/fuel mixture gauge. For all you know your air fuel could be optimal now and if you lean it out for more power you could melt stuff down. You could also read your plugs to see how your mixture is, if your not sure how to do that search the net there are a lot of good articals on how to read plugs when using nitrous. Also, just courious, is your bottom end stock? If your not running forged internals you probably shouldn't be running over a 150 shot anyways. Cant wait for summer so I can get out and start feeding my 79 vette more nitrous. It likes it!

 

Bottom end is stock. Had it dyno tuned and it ran a little rich in the midrange at 51 PSI. Don't think I'll go any lower than 45 PSI to see what the power gains are.

 

Good luck. Maybe go back to were you had it dyno tuned and they can keep an eye on your A/F mixture while you dial it in for max power.