Engine & Driveline
Jim Conforti Chip
Overall, this will give you the best performance improvement per dollar in a 318iS. It gives an additional 12hp at 5500rpm and 15 lb-ft at 2500rpm. The car definitely feels more responsive with the chip and accelerates more smoothly. I ordered mine through Turner Motorsport. The cost is about $250, and is well worth it. Do not buy knock-off chips on eBay and that sort of thing. As they say, you get what you pay for.
I have been running SuperSprint cat-backs on my 318iS since 2002. They are high quality units that have a mellow, but quiet tone. The price of these units is rather exorbitant now since they are out of production. Occasionally, once enough orders are placed for the E30 318iS model, SuperSprint will do a small production run. I had to wait about 9 months to get my unit after placing an order with BMP. The cost was approximately $600. There are many other, cheaper options out there that sound about as good & will last a few years.
These pictures are of my first cat-back unit. The ones you get now are two pieces, and there is no resonator.
Catco High-Flow Catalytic Converter
I usually install these because they are the least expensive California-legal catalytic converters available. It is extremely unlikely that they provide any performance improvement. The stock catalytic converter has a huge core, which is actually perfectly fine for performance because it allows for a larger cross-sectional area for exhaust flow. The stock ones are not legal in California, and even if they were I would not spend the requisite $1000 or more on one. The Catco units are of the "3-way" type with a NOx scrubber section, so despite their smaller size (as compared to stock), they probably do a better job of decomposing the exhaust gasses since the stock ones were all "2-way" units.
Innovate Motorsports LC-1 Wide-Band O2 Sensor
I purchased this during my MegaSquirt conversion on my first car. Aside from being a useful tool for future tuning, replacement sensors of this type are about 1/3 the cost of a new OE one, and are superior units (Bosch LSU4.2). The new car does not have the MegaSquirt installed in it, but the WBO2 setup has been indispensible for my MAF conversion and custom datalogger projects. For $200 from Innovate Motorsports, this is an unbeatable deal. It can be used as part of a modular tuning system, or used for logging alone. It has digital outputs, as well as two fully programmable analog outputs, and can simulate a Narrow-Band O2 sensor. This means you can run the Motronic from it, AND log the AFR on the other channel at the same time! Be warned though, the Bosch wide-band O2 sensors that this uses are easy to burn out. Running one of these does take periodic work to recalibrate the sensor.
Custom MAF Conversion
My senior engineering project was do design a working MAF conversion for the M42. The original version worked, minus a little glitch that occured around 4200RPM where things ran a tad rich. Months later I revised it to use a Bosch sensor that fit the engine's air box with a $5 rubber coupling (versus the original Ford sensor that would not work with the air box). So far I have put over 20000 miles on it and it has performed well. There are no power gains to be had with it, but htrottle response is better and the idle is a little smoother. Presently, the converter uses a 255 tap FIR digital filter sampling at 8kHz. This is necessary because of the terrible acoustic resonances that occur in the M42's intake system.
M20 Flywheel Conversion
This conversion was somewhat of an ordeal, but well worth the trouble in the end. It requires a late-model M20 flywheel (single mass), M20 clutch disc & pressure plate, matching starter pinion gear (the whole assembly, not JUST the gear), AND an E21 323i throw out bearing. You also must remove the spacer ring from the M42's flywheel and use it to keep the M20 unit from hitting the upper oil pan, and order some M20 flywheel bolts. Installation is relatively easy once you have all of the parts. The only real challenge is disassembling the starter as it tends to get very rusty and the screws are nearly impossible to remove. Once done, a marked increase in performance can be noted in the first and second gears. The idle does suffer a tad, but it is still plenty bearable.
Custom Coil-On-Plug Ignition Conversion
After tiring of replacing the expensive ignition wires, I decided to look into developing a COP (Coil-On-Plug) ingition retrofit. Since the M42 already uses coil-per-cylinder ignition, all that was needed to do this was some new ignition coils and a way to mount them on the valve cover. Initially, I attempted to do this using the stock coil packs, but that required a lot of chopping and it was nearly impossible to fit the connectors on them when in place. With some collaboration on the M42Club forums, I found that the coil packs used on most E46 cars fit very nicely. After some prototyping and thinking, I finally got it right. I even found a way to disassemble the connectors so the factory harness could be trimmed to a proper length. See the pictures below for shots of the development and the final product! Check out the full story in the Pictures, Projects & Stories section!
Small-Case 4.10 Limited Slip Differential
In April of 2008 I installed a limited slip differential that I purchesed from a forum member for $200. Rear wheel traction is greatly improved on dirt and wet pavement. At the same time, cornering takes a little more work, and the car is more unforgiving of oversteer mistakes. It is all a trade-off, but it was worth it for my needs.
TRE Performance 255LPH Fuel Pump
When the stock fuel pump started to die, I opted for a higher capacity fuel pump. Installation required some minor modificaitons to the stock fuel pump bracket, but everything fit into the tank without too much trouble. There is not much need for an uprated fuel pump in my car since it has a fairly stock motor, but this pump was less expensive that the stock one and has received good reviews for reliability.
Bosch 0 280 155 700 204cc/minute Fuel Injectors
A slight improvement to performance and idle stability can be realized by installing these fuel injectors. They are rated to flow about 6% more than the stock ones, which the ECU can handle through the oxygen sensor. However, the big improvement with these is the pintle technology. The stock injectors use one large pintle in the center of the outlet. These newer ones use four smaller pintles, which leads to improved fuel atomization. I purchased a set of 8 on eBay for about $75 and paid another $40 to have them flow tested for uniformity. I am not sure if any power is gained with this change, but the engine does seem to run more smoothly.
Z4 Shifter Linkage & Rod
When the stock shifter linkage finally wore out, I opted ot install the parts from a Z4. This provides a shorter throw between gears without too much more effort, and it eliminated a fair amount of shifter slop. The total cost for the kit was $95 from BMA Parts, and installation took under 2 hours. It is a worthwhile upgrade for someone that needs to replace their sloppy, worn-out stock shifter.