[Obioban]

Bolt on (intake/exhaust/cam/tune) S54s get up to ~360-370 SAE RWHP these days.

Bolt on FI takes you to ~450 SAW RWHP.

More extreme FI has gone up to ~1200 crank HP, but that some pretty serious building. And, honestly, WAY too much power for the chassis to handle. I think the e46 chassis is pretty ideally suited to ~500 crank hp.

If you're looking for cheap power, ebay headers (with their associated possible leaks, fitment issues, etc) and a DIY tune (easy these days) nets 25-30 hp for ~$200.

S54 tuning has really moved forward in the last two years!

I'm in the boat that FI is satan, so my car is currently sitting at 328rwhp... but I have a CSL intake on the way, as well as CSL based ECU tuning (MAP sensors instead of MAF), and hoping that will push me to ~340rwhp. Then I kind of want cams. After that, not doing anything till I need a rebuild (fail a compression/leak down test, hopefully not until ~250,000 miles). At which point, thermal coatings, bump it to 12:1, maybe a slight displacement increase.

Once I'm 12:1, I'll remap the sport button to be a 93/91 octane switch and retard timing to keep her from knocking when on 91.