Why did you choose the E46 platform?
BMW has a long history in road racing, and the E46 has been successful in both amateur classes (NASA GTS, BMWCCA Club Racing) and professional series such as Grand-Am.

  • Inexpensive to buy. Donor cars can be had for under $4k, and 6 or 7k will get you a really nice one.
  • Inexpensive to run. Without a stratospheric rev limit the fuel burn is kept in check, 17″ tires are towards the low end of the price spectrum, and the stock brake rotors won’t break anyone’s budget. Wheels utilize a square setup (same at all four corners) which makes tire rotation and wear leveling easy.
  • Durable. The M54 motor is one of BMW’s best – smooth, reliable, and easy to work on. Transmissions, especially the ZF five speed, are proven performers. And with so many cars sold parts availability, both new and used, is excellent. Like most modern BMWs the cooling system contains plastic parts that require periodic replacement, and the chassis needs a few strategic reinforcements to withstand track abuse but these issues are well understood and easily rectified.
  • Fast. The E46 has a modern chassis that is low and wide, and fits large racing rubber with ease. The dual VANOS motor has a broad powerband and pulls nicely to redline. Smoother aerodynamics slice through the air with less drag than the E36. The stock 330 brakes, larger than those fitted to the 325/328, have enough capacity to repeatedly haul the car down when paired with track pads. Most importantly, we’ve spec’d high quality dampers and other suspension components to ensure that the suspension system isn’t a limiting factor in the car’s performance.
  • Fun. The E46 has several features that make it easy to enjoy as a race car. The suspension is sufficiently adjustable to allow drivers to tune their cars to maximize performance and suit their individual driving styles. Two or four door models are available if you prefer one over the other. Modern electronics provide sensor inputs like throttle position and steering angle to feed your data acquisition system. The body style is widely considered one of BMWs best looking. But most of all, they’re just great driving cars.

Why are only 330-based models allowed? Can’t you allow 323/325/328 models?
There are several reasons we have chosen to permit only 330-based models (excluding the 330 ZHP).

  • First, power; we wanted the highest output motor possible without going down the M3 path.
  • Second, different motors would require different competition weights and in our experience, it is extremely difficult to achieve the desired balance between the different models (see: Spec Miata).
  • Third, there are other differences between the models besides the motors (such as brakes) which would be difficult to account for in a fair and equitable manner. The most important part of spec racing is ensuring that all cars are as similar as possible, and that means one chassis/motor.
  • That said, Spec E46 allows for 323/325/328 models to be converted to Spec E46 provided all of the 330 parts are swapped over. It’s a non-trivial amount of work to do this but it can be done. Allowing other E46 donor chassis increases the total number of donor shells and parts available long term.

Wouldn’t it make more sense to use the E36 or E46 M3?

  • The E36 M3 has been a track day favorite for many years – it’s fun, durable, reasonably light, has excellent brakes, easy enough to drive for beginners to get started on while being fast enough to excite experienced drivers. However, there are several reasons we did not select it:
    Many existing track day cars have been modified with parts that would not be compliant with a spec race series and would have to be removed or replaced.
  • The platform is getting on in years, the newest E36 you can buy is still fifteen years old.
  • There already exist two spec race series based on the E36 platform, Spec3 and Spec E36. The world doesn’t need a third.
  • Fitting wide race rubber can be a challenge, even 245.40.17 R-comps often require wheel spacers and fender rolling.
  • It lacks stock sensors which many racers find invaluable for data acquisition such as throttle position, brake pressure, and steering angle.
  • The E46 M3 is a wonderful track car. Fast. Beautiful. Great chassis. Amazing engine. Plenty of “wow factor”. So why not use it? In a word, cost.
  • Even tired donor cars cost 12k, and good ones can easily top 20k.
  • As lovely as the S54 motor is, it also isn’t cheap to replace (and is notoriously hard on rod bearings). Ditto the transmissions.
  • 18″ 275mm tires + M3 pads and rotors + faster fuel burn = higher consumables cost.
  • Not available in a four door, a body style many people prefer for its ease of access to the back of the car.

Why the fancy suspension? Spec E30 utilizes inexpensive parts; why can’t Spec E46?

One of the design goals of SE46 was to create a car that was fast and fun in both racing and non-racing environments. With a great chassis underneath, we felt the E46 would be let down by low end, non-adjustable suspension components. What worked for the E30 in 2005 isn’t necessarily the best choice for the E46 today. We also wanted a platform that enabled drivers to develop their skills in tuning a race car chassis, something that non-adjustable cars can’t deliver.


Why isn’t Component X a spec part?

While mandating spec parts is good for vehicle parity, single sourcing any component has numerous potential drawbacks.  Vendors often change or raise pricing.  Sometimes the parts are redesigned or even discontinued.  There’s also the possibility that a vendor goes out of business, has a supply challenge, or even produces an inferior quality part.  We’ve spec’d the essential performance parts (tires, springs, shocks, exhaust, and ecu) and required that many others remain stock to maintain as much vehicle parity as possible while giving racers enough flexibility to build and set up their cars to suit their tracks and driving style.


Why is the differential open (unregulated) aside from ratio?

Differentials are complex items with performance characteristics that are not quickly or easily measured without highly specialized equipment.  A simple test such as torque breakaway tells only a small fraction of the story and is therefore an unreliable indicator of performance.  They are also non-trivial to remove and inspect, making trackside enforcement of any rules difficult.  Because there’s little point in writing specs that are meaningless or rules that can’t be enforced, we left the diff rules mostly open.  We also felt that with modest power output and good suspension the effect of the diff would not be a major source of lap time variance.


Why was my post deleted from the Facebook page?

In order to keep the signal to noise ratio high, only posts that are directly relevant to Spec E46 are permitted.  The group admins reserve the right to delete any posts they feel do not meet this requirement.