This thread has gone off topic way too many times. OP asked about perf. upgrades to a 323 not a 335. And back on topic, sell car, buy another car, or be happy with what you have. Spending $'s on power upgrades is a waste of time and money, you'll never be happy. Or, you'll be in a Tim's parking lot bragging to others how with your so and so you've got 12 more hp and with that thingamabob you've got 7.5 more hp so now you should be pushing close to 200hp! Wow I'm so sure everyone will be so impressed when the reality is, you might have gained half of the claimed hp. mktg mktg mktg! Not to mention, the actual speed gained if measured on a track will NOT be noticeable.
I remember years ago, my know it all bro-in-law was telling me how all of these bolts ons added almost 50hp to his e36 m44 318i and how much faster his car was because of it. FEEL it come on isn't it amazing he said. Stock we had gone to a cayuga test and tune the month before and he ran a 16.7 sec 1/4. After this almost 50hp increase we had gone back and guess what he ran? 16.6 sec 1/4, which I attribute more to the cooler weather than to the upgrades. I never noticed much of a difference other than a higher redline. Nonetheless, he made excuses and I would still blow his doors off with my stock vr6 jetta which would run consistant 15.3's and blah blah bla.
Then I got an e36 328i and did a 14.7 first pass and that was that. He shut up, sold his car and went in a different direction with a dsm awd turbo. (I still beat him with my e36)
BMW F30 335i M-sport - SerpaBMW Company Art car
BMW 325I E30 Track Rat
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BMW 540iT M-Sport (New Family Hauler)