Things I Didn't Keep
This page lists a multitude of modifications I made to my cars over the past decade (and counting) and subsequently rid myself of. They were removed because they served no purpose, served a purpose that was inappropriate for a street-driven car or were just more trouble than they were worth. Consider this an advice section that can save you time and money. As I have found over the years, a meticulously maintained stock E30 is a very capable performer on its own. A big plus with a stock one is that it is far more pleasant to drive. If you are not using the car for track events and it is a primary mode of transportation, most "performance" modifications are a bad idea.
Custom Intake & Heatshield
This modification was made on my first car when I was in high school (sometime in 2000). At the time it seemed like a good idea. For whatever reason, it is easy to convince teenagers that the engineers at car companies do not know what they are doing, and that all stock intakes are robbing them of precious horsepower. The open element filter certainly sounded neat. Alas, these things are a gimmick, and at least in an E30 with an internally stock motor, the stock air intake is the best system. It IS a cold air intake system that has been designed to work with the intake resonances inherent to the motor. No matter how restrictive it may look, it is better than whatever sordid aftermarket junk one might scrounge up & stuff onto the intake pipe. It is also a good idea to stick with stock paper filters. "Performance" filters let in a lot of particulate matter, with negligible air flow gains in stock applications. Do your old motor a favor & trust the engineers at BMW.
Polyurethane Differential Mount
I used one of these for a few years. It seemed like it might provide an improvement in driveline feel and performance. It was also a lot easier to install than a stock one (and being a broke college student at the time, saving $40 in shop labor was a large factor). Really, this part served no useful purpose. It wore out after a few years and allowed slop in the rear suspension. Now that I use a beefed-up stock rubber bushing, I am quite happy.
BavAuto 8mm Ignition Wires
There is not a lot to say about these. They are a gimmick and do nothing. Get new stock wires if yours are work out. There is no such thing as "performance ignition wires" for these cars. End of story! Don't be silliy like I was and spend $180 on these.
M30 Engine Mounts
I used these for a number of years because they cost 75% less than stock M42 mounts, and they were far stiffer. They did make a small improvement in throttle response since the engine is held more rigidly with them, but the noise and vibration became too much to handle on long drives. They are an OK swap for someone on a tight budget, but stock mounts are worth the extra cash. You will have to put up with a substantial amount of noise and vibration with M30 mounts installed under an M42.
H&R Sportline Springs & Bilstein Sport Gas Shocks
This kit was a lot of fun. The car felt like it was on rails. Eventually, the rough ride and constant scraping on driveways got old. The last straw was an incident where a rock put a hole in the oil pan when I was driving on a remote service road in the middle of nowhere. These are not a great idea on a street car, but if you are really careful you might enjoy them. If you like to take your car to a variety of places with widely varying pavement quality, stick with stock parts.
Racing Dynamics Strut Tower Braces
I used these on my first 318iS, and the front brace did seem to stiffen the chassis a little. Cornering may have improved a little. When that car was destroyed in a crash, so were the braces. The front one did save the motor, which I was able to sell for $850. I have not replaced these items on my second car as I do not feel that they provide a significant improvement in anything. The do help with weight reduction in your pockets, but I try to keep those heavy these days.
Polyurethane Control Arm Bushings
Stick with stock rubber parts. Yes, stockers are more work to install, but they really aren't robbing you of anything on a street car. I used some 1996 M3 bushings that have much thicker rubber webs than the stock E30 ones. They are also the centered ones, not the offset ones that seem to be very popular.
Polyurethane Rear Subframe Mounts
Again, stick with stock. These provide negligivle gains for a street car, and they transmit a lot of noise and vibration into the car.
Polyurethane Rear Trailing Arm Bushings
By now, you should know what I am going to say. Yes, stock is what you want if you aren't tracking the car. I had constant problems with these bushings squeaking too, which is another reason stock rubber ones are advantageous.
Camber Corrective Front Shock Mounts
These items were used with the lower H&R / Bilstein suspension that I mentioned earlier. A stock suspension does not need these. They are not really performance items, but they do help with tire wear issues seen with lowered suspensions.
E28 535i Brake Master Cylinder
This is a very dangerous modification. Do not do it. It upsets the brake balance, and the rear wheels lock much more readily under hard braking. Bigger is not always better, take my word for it.
Solid Brake Caliper Carrier Bushings
I removed these items. They did not seem to do much for braking performance. They did manage to sieze one of my rear calpiers though.
Mild Weight Reduction
I removed the air conditioning and much of the interior. This was sort of pointless, but it seemed like the "thing to do" for autocross. My current vehicle has not been stripped down, and is much more comfortable to ride in.
Corbeau A4 Seats & 4pt. Harnesses
I purchased these for my first 318iS. They were nice to have at autocrosses since they held me in place very nicely. They were ruined in a car accident. The factory Recaro sport seats that the E30 come with are almost as good as these if they are covered in cloth. It is also unsafe to drive with four point harnesses without a roll cage. Four point harnesses prevent you from ducking in the event of a roll-over.
Custom One-Touch Window Controller
I developed a one-tough window controller that worked with all the stock E30 hardware. It used a PIC16 microcontroller and some miniature power relays to control this functionality. It was later removed due to a couple of electrical bugs in the design (mainly related to the rat's nest of wires being susceptible to EMI). They were pretty easy to fix, but for now I do not really see much use for one tough windows. They are convenient, and I may build another, improved controller to use someday.
Hella H4 Headlights
These were a great, inexpensive lighting upgrade. I eventually sold them and installed Euro ellipsoid headlights. I highly recommend these to anyone who does not want to spend $300-600 for the ellipsoid units. You should NOT use HID kits with these though. You will be a road hazard at night if you do.