Welcome to the forums Lauren -
hope you enjoy browsing the forums as much as i do.
there is so much info on this site, it ist funny, so before you post something - be sure to search and you will...
i recent upgraded to rear disc brakes - changed brake master cyclinder - didnt change the prop valve. is 150% better in terms of feel and stopping power.
Disclaimer: The following is provided as a GUIDE ONLY, and neither myself nor Ozhonda take any responsibility for the outcomes of someone else doing the following. You follow these steps at your own...
if you want to go turbo - boost the d16a8, most bang for buck.
if you want to go all motor. b16a, as most people have suggested, is definately within your budget.