Here I will make it easy from 3800 Forum

"This section is for those looking to go as far as they can for minimal money and to get the best 'bang for the buck':

There is a very simple and straight forward list to obtain approximately 300 crank horsepower (~240whp) and to be able to run high 13 second 1/4 mile times (with minor track prep- in full street trim).

-CAI/FWI, (the most common used is the 4" inlet, 9" long K&N, but many will work), you want as little restriction and as little temperature as possible for the s/c to provide the coolest output. Do not do a 'hot air intake' with the filter in the open engine bay at this mod level. This runs $50-300+ and power gains are minimal, but you will now hear the supercharger scream when you floor it!

-Downpipe, do a 3"- this eliminates the neck down right inside the first bend of the DP, and eliminates the ubend. These things are cheap if you don't need a cat, but even with a cat, they are worth it $80-200

-Plugs (while plugs are useless for an L36, the stock platinum plugs do not work well with modded L67s). For this step either go with Autolite copper 605s (1 step colder than stock) or Autolite copper 104's (2 steps colder than stock). If you don't plan on going further than this list- go with the 605s. Less than $10

-180* thermostat- just another mod that seems to help w/ KR reduction $15

-ZZP Powerlog- basically a front header only- eliminates the neck down point just before the crossover pipe, and is a very quick and easy install ~$100.

-1.9:1 modded stock rockers- open the valves more, letting more air in and out. These are the most difficult part to install of these basic bolt ons, you pull both valve covers to change them- but you can leave the stock springs, and driveability and gas mileage stays about the same. These are the second most noticeable power gain next to the pulley drop. Prices range from $200 used up to about $275 new.

-pcm tuning- you essentially have 2 options here- a canned tune that they send you a new pcm, or driving to someone and having them custom tune it. A canned pcm is far cheaper at $100, but its gains are typically nowhere near a one off tune. Honestly, if you plan to spend the $250+ on a custom tune, you should consider buying your own tuner (they start at $400 for the 3800s)- but be prepared to learn... A LOT.

-supercharger pulley drop (if you will stop modding at this point- go with a press on pulley- if you plan to go on, then buy a modular setup so its easier to change again later)- you do need to scan for knock first- after all those other mods are done. If you still have knock, then you probably have a problem. If not, you're good to drop pulley sizes. With those mods above, you should be good to go for a 3.4" pulley, however, if you had a very hard time getting rid of factory KR, and you barely did- a 3.5" pulley would be a better choice. This is likely the most significant power change for the basic bolt ons, as long as you end up with little to no KR. Press ons go from $20-60, modular setups go from $80-150."