I'm running the BTC/MAP sensor on my JRSC currently. I'm going to be upgrading to 440's and either S300/Neptune next week. My car hasn't been dyno'd as is but does anyone know how much additional hp (roughly) I can expect on a full tune?

 

It's really hard to give an accurate number. It depends really on the skill of your tuner and your particular set-up. If the car has not been tuned i would expect to see a "healthy" gain with a proper tune