Lately I’ve been putting some thought into building a dual use road/track car. Something that would be possible to do my commute to work with, but also have fun with on a track during trackdays. Inspiration came from HeelandToe.Blog’s 328i and the two Throttle House cars. Grassroots Motorsports also is a good resource. If you can read German (or want to use Google Translate), docweb-racing and m3racing have E46-specific information.
Using a BMW E46 is a no-brainer, as it is one of the most affordable suitable rear-wheel drive cars for such a project. The E36 used to be a favourite, but is getting older and scarcer, while the E46 is still plentiful. Engine-wise, the choice is easy, too: the 231hp M54B30 as used in the 330i is the way to go. The power increase compared to the 325i is significant enough to warrant the slight premium you’re going to pay. On the other hand, while an M3 might sound even more attractive, prices are now such that I cannot recommend an M3 for such a project. Many parts are also M3-specific, resulting in higher parts and maintenance costs than with the 330i.
Concerning body style, convertible and touring are not really an option (consider the latter if you really need the extra trunk space) and the compact was only sold with the 325 engine, so sedan or coupé is where it’s at. I lean towards the sedan – it is a bit stiffer, might be a bit lighter (at least the E36 sedan was lighter than the coupé), and rear seat access is easier, especially with racing seats fitted. The coupé has the looks advantage.
You of course don’t want an automatic transmission, and I’d stay away from the (pretty scarce) SMG gearbox, which is a different model than the gearbox used on the M3 and is mostly known for expensive maintenance. The 330i was sold with a five-speed manual and then a six-speed starting in March 2003. The ratios of the six-speed are the same as the five-speed (with a longer sixth gear added on top), so it’s desirable only if you do lots of highway travel and want to keep the revs down, or plan on installing a shorter diff and still want top speed for really fast tracks.
Options are really dependent on your own preferences. I would skip sunroof cars (weight up high, and some racing classes don’t allow them). If you plan on sticking to the factory seats for the time being, I highly recommend getting a car with the factory sports seats as they offer a much firmer hold than the standard seats. In general, I would go for the most original car you can find instead of a heavily modified one, especially if you want to compete in e.g. an autocross/slalom class that requires a car to be mostly original. Original cars are also often the better maintained cars. Check the maintenance history, look for signs of rust and oil leakage, ask whether the VANOS has had a rebuild, and if possible check the car’s rear bottom for cracks. Stay away from cars built before september 2001 as these are prone to developing cracks here. There is some disagreement as to whether this has been solved after or still occurs, so checking really doesn’t hurt.
Before embarking on upgrades, consider whether a) you want to be able to return the car to original state at some point, and b) if you plan on competing in events where certain modifications will have you placed in a modified class, where you might end up against much faster competition.
Tires & wheels
Tires are the most important upgrade you can make. In my opinion, there are two options. If you use the car mostly on the road and thus require good grip at all times, including in the rain, I would go with a good standard summer tire. I run the Continental Sport Contact 2 on my compact. These are quite affordable, well balanced for daily use, and should be forgiving on the track. If track use is your main goal, something like the Michelin Pilot Sport Cup 2 will give you more grip at a price that is still Ok. Keep in mind that tires with more grip usually lose that grip more sudden than a tire with less grip, making them more difficult to drive at the limit. Performance in the wet will also be much worse.
The 330i’s brake rotor size mean that 17″ is the minimum wheel size you can fit. I would not go larger, as bigger wheels just add more weight. Mixed wheel and tire widths are pretty common on the 330i (225s up front, 255s in the rear), but this may lead to understeer. I’d recommend a “square” setup on with 245s on 8 x 17 wheels, with the added benefit that you can then swap wheels between the front and rear axle.
OEM wheel weights are given at BMWStyleWheels, BMW-Treff, and e36racing. There seems to be little weight difference for 8 x 17 wheels, which may or may not be due to inaccurate numbers – the style 32 wheel is by far the lightest in 7 x 16. Popular lightweight aftermarket wheels are Apex and Enkei, but these seem be difficult to find with the correct offset (ET should be 47mm) which may lead to handling issues or problems if you are in a country where there are strict rules concerning car modifications. Since used OEM wheels are cheap and easy to find, I’d stick with them for the time being.
One of the advantages of the 330i is that it comes with bigger brakes than the 325i, and apparently these work better than on an E36, too. The general consensus seems to be that sticking with the OEM rotors and upgrading to better brake pads works best. Products by Pagid and Hawk are popular, Ferodo also has pads geared towards road/track use. Brake cooling ducts may be a good idea. Grassroots Motorsport has a good article on the subject.
Steel-braided brake hoses and high boiling point brake fluid are modifications that aren’t expensive, so definitely worth giving a try. Castrol SRF is expensive, ATE Type 200 a bit cheaper. Fischer makes steel-braided hoses that come with a German ABE certificate.
There are some misconceptions about the role of shock absorbers, springs and sway (anti-roll or stabilizer) bars. Some people are in the “as low and stiff as possible” camp, and an often-heard thing is that bigger sway bars will reduce grip at the axle where they are applied. My opinion is as follows:
- Very stiff cars will be bouncy and lose grip and traction on rough roads. I would lean towards soft, which has the added benefit of being more comfortable on the road. A softer car will also announce the limit more clearly, making the car easier to drive (not necessarily faster).
- Excessive lowering may screw up your suspension geometry and make the car unusable on public roads (speed bumps!).
- Sway bars reduce body roll, which means that a) the car settles faster in turns and b) there is less camber change, which is a good thing.
- Sway bars affect load transfer, meaning that the front and rear sway bar can be used to fine-tune oversteer and understeer characteristics of the car. From the factory, cars will be tuned more towards understeer. Adding an even bigger front sway bar will only worsen this!
- The biggest improvement may be gained from adding more negative camber to the front. In order to achieve safe (understeer) characteristics, the factory setup has more negative camber on the rear than on the front.
- Having the car aligned after suspension changes is essential.
As a result, you may consider the following:
- Camber plates, which may not be legal for the class you want to complete in.
- Lowering springs (Eibach and H&R are good brands) and stiffer shocks (e.g. Koni, Bilstein).
- A coilover set – the name is a bit strange considering the E46 has standard coilovers up front, and shocks and springs are always separated in the rear. The German term Gewindefahrwerk (threaded suspension) fits better – height-adjustable suspension that often also allows adjusting the dampers. KW and Bilstein are the most popular brands here. These often also come with camber plates.
- Stiffer anti-roll (sway) bars – Eibach, H&R and KW come to mind here.
- Polyurethane bushings (Powerflex is a popular brand) tighten up the handling.
- Strut bars stiffen the car.
Interior & weight reduction
Weight reduction by ripping out the rear seats, carpeting, sound-deadening material and even the door panels (the innards will then have to be covered up by a new, lighter panel) is relatively easy to do and, best of all, cheap! However, on a car that still sees regular road use, I would not recommend to go further than removing the rear bench seat before hitting the track. The same goes for deleting the airco. Sure, it saves weight, but you’ll sorely miss it stuck in traffic on a warm day. You can install a lightweight battery, the benefit is somewhat limited due to the battery already being installed in the trunk.
You can both save weight and sight tighter by upgrading to racing seats. Depending on regulations in your country, the choice can be limited. The Recaro Pole Position ABE comes with a German certificate. Installation may be non-trivial. If you install two non-folding seats in a coupé, the rear seats will be inaccessible. Replacing the passenger seat will also require a solution for the seat occupancy sensor.
The best OEM steering wheel is the M steering wheel. You can easily switch over the air bag if you have the standard sport steering wheel (with the round air bag panel).
A four-point or six-point harness will further tighten you down. About half of the Internet will tell you this is suicide without a roll cage as the roof coming down during a roll-over will crush your head in, so this may or may not be a good idea.
If you plan on heavy track use, I can’t recommend a roll cage enough. It will also be mandatory for most real racing events. You can either go for a bolt-down cage (it will still be necessary to weld in mounting plates) or a welded cage – the latter also stiffens up the car, which is why it is not allowed in all racing classes. At this point, the car loses its daily usability, and you might as well go the full monty with a six-point harness and any weight reductions that are allowed in your class. German group G rules e.g. require the presence of the rear seats and the original door panels!
It is recommended to drive a car with roll cage with helmet only, as an impact head – cage will otherwise lead to serious head trauma.
Check the cooling system. Older hoses may be brittle and burst, so on a car with unknown history, a complete set of new hoses may be a good idea. Consider a VANOS rebuild. You can do it yourself, it takes a couple of hours. Replace the oil. I’m a supporter of 0W40 for daily use. For heavy track use, 10W60 is recommended, but this may be too thick for daily use.
The M54B30 is known for shedding a nut on the oil pump at high revs, which will lead to a failure of the oil pump, possibly with a destroyed engine as result. A modified nut is available, as are high-performance oil pumps. This seems to happy especially to cars that have had the rev limit increased.
The 330i has the longest diff of all the E46s. A popular modification is the 3.46 diff from the automatic transmission car, for better acceleration. Unlike the E36, the E46 (except for the M3) was not offered with limited-slip diff. Aftermarket kits are available. A lightweight flywheel is another thing you can consider.
Getting more power out of a naturally aspirated engine is expensive. That’s why many racing classes (e.g. Spec E46 in the US) don’t allow it. Your best starting points would probably be headers and an M50B25 intake manifold together with engine remapping. Beyond that you might just as well save some more money and get an M3.