i have put a slp single pipe and air horn kit, now iam up in the air about putting the FLOW RITES i know slp says it is required to get all the HP.but i would like to hear from some people that have had good luck with it.i sure would hate to drill the hood if its no needed so what do you guys think??????

Well I have not run them or a slp pipe, but IMO it makes sense. If you gut your box and add a pipe I would think you cant be sucking through a pin hole--if you know what I mean.
Yes SLP is in business for a profit, but I dont think they base sales projections on flowrite sales. Also, SLP and others realize most people wantto leave sleds looking as stock as possible.
All that said - Yes I would imagine they are well worth it. Now what SLP says to jet vs people on here is much different, and I am not touching that topic, because I ve heard from 410's(700) to 500 (700)

Good luck ,and please share your experience when the snow flies

They will help, but use TPI lowboys. That way you can open and close them depending on outside temp. It's like jetting with air. I have four lowboys in the my airbox. I jet my carbs so its safe to have all four open at 20F or above. When the temps drop I can close or partially close the lowboys to keep my jetting safe.

The problem with the other solution is that they are mounted to your airbox. You need cold fresh air - hence the location in the hood.