THE GURU:
John Vitamvas has spent the last two years developing an E46-chassis BMW for D Street Prepared. His red 330Ci has been a fixture on the National autocross scene since the early 2000s.
THE PITCH:
Three generations of BMW 3-series compete with the Mazda RX-8 to create one of the most crowd-pleasing classes in Solo. Ripping inline-6 cylinder and rotary engines, big fender flares hiding monster tires, and friendly competitors are the staples of this class.
THE SCOOP:
The six-cylinder BMW 3-series is a proven formula, with the E36 and E46 chassis being the most popular choice, though the lightweight E30 has seen a recent resurgence as Kevin Henry and Tom Bleh have wrenched and wheeled their cars towards the top of the results sheets.
Because of Street Prepared's update / backdate allowances, your starting point can be the most plebian E36 323i or the most highly optioned E46 330i. If you start with one of the smaller-engine cars, you’ll want to swap in the largest engine available for your chassis. In the case of the E46, that would be the 3.0L engine from the 330i/Ci, and ideally it should come from a car with the ZHP package as those cars have slightly hotter cams. No matter the starting point, a solid 80-90% build can be accomplished by addressing three major shortcomings: suspension, differential and rolling stock, the same items that would be addressed in an STX BMW build.
Most of the DSP grid is suspended by Moton or AST dampers as they work very well on the choppy Lincoln concrete. Naturally, you’ll want loads of negative camber dialed in up front using aftermarket camber plates. While the E46 enjoys a wide range of factory-available gear ratios, from a 2.93 to a 3.46, you’ll need a quality limited-slip differential with lockup characteristics appropriate for Solo use. Even after shedding weight with lighter seats, exhaust and a non-airbag steering wheel, these are heavy cars: around 2,500lbs for an E30, 2,700lbs for an E36 and 2,900lbs for an E46. As such, wider wheels and tires are one of the first upgrades you’ll want to make. The typical setup for the E36/E46 chassis cars is the ubiquitous 285/35/18 Hoosier A6 mounted on 18x10” wheels, but other options exist, from the 275/35/15 Hoosier A6 all the way up to monster 315/30/18s. Fitting these big meats requires fender cutting and flaring regardless of the chassis, but this can be accomplished with aftermarket plastic flares if bodywork isn’t your forte.
For more power, these cars respond very well to readily-available and inexpensive long-tube headers, a well-engineered merge collector and a 3” exhaust that exits just before the rear differential. This setup has the added benefit of allowing the axles to be replaced without removing the exhaust. For an intake, run a long tube down into the front bumper to capture air outside the engine compartment. It doesn't make much difference in terms of power, but it sounds glorious.
Once you get all the hard parts installed you’ll need to tune the thing. Very few people have the tools and knowledge to tune the E46 engine computer, and they charge a lot of money for the privilege. Another option is to ditch the factory BMW setup and run an aftermarket EFI system like a Megasquirt 3. Peter Florance of PFTuning.com has these systems running reliably in at least three National-level DSP BMWs and is a one-stop shop for converting your BMW to tunable EFI. Be aware that while the iron-block E36 engines are pretty robust, the E46’s aluminum-block M54 engine is known to be unreliable beyond 7,000 RPM. A harmonic balancer from ATI helps improve reliability in sustained high-RPM operation, and these engines don’t make much power past 6,000 RPM anyway.
THE PRICETAG:
A competitive DSP BMW is not particularly expensive to build from scratch, and a well-built STX BMW is a great starting point for a DSP build – just add fender flares and wider wheels with sticky Hoosiers, increase spring rates and you’re most of the way there. The flip side is if you start from scratch you can build the car up gradually and make intelligent choices as you learn the car’s shortcomings. A basic, high-mileage E36 chassis can be had for $1,500-$3,000 while an E46 330i/Ci can be had for less than $6,000.
Tons of 18x10" wheels from DForce and Apex are readily available for these cars, and 18x11" wheels are available if you want to run 315mm tires. Figure $1,000 set or half that for used ones if you scour the forums. A set of Moton or AST shocks will run $2,000 for a used set up to more than $6,000 for new ones with custom valving. You’ll want multiple pairs of standard coilover springs, a set of aftermarket adjustable anti-roll bars for fine-tuning, plus a set of camber plates (Vorshlag makes a really nice set for around $600) and adjustable rear camber arms. Flaring the fenders can be pricey for all-metal, welded-in flares off of an E46 M3, but a body saw and some rivet-on plastic flares can accomplish the same thing for much less if aesthetics aren't important.
Headers ($300-$1500 for off the shelf eBay specials or the genuine Supersprint's they imitate) and a custom header-back exhaust ($300-500 in materials) can be built by any good exhaust shop as the routing is very simple under the E36 and E46. A quality aftermarket differential from a known builder (Blanton, Jim Rowe, Diffsonline) will run upwards of $3,000 new, but used units do regularly come up for sale on the forums so keep your eyes peeled. You can also build your own starting with an OS Giken LSD unit, but be aware that special tools are needed to assemble and set up E46 differentials so you may want to leave this to a pro. The less expensive E36 differentials unfortunately do not fit in the E46 case.
A lighter flywheel and a stronger clutch assembly help the car put power to the ground and there are plenty of aftermarket options. ACT sells a nice clutch and flywheel setup for the E46 chassis that Strano Performance Parts will be more than happy to source for you. It retails for around $1,200.
THE HONEST TRUTH
It's no secret that E36- and E46-chassis BMWs have some reliability problems, such as cooling systems made entirely out of plastic, fragile differential mounts and subframes and (in the case of the E36), fragile axles. OEM BMW parts aren’t particularly expensive and it’s good insurance to replace the coolant hoses, pump, radiator and overflow tank. In general, the stock BMW rubber bushings (including differential and subframe mounts) are very long-lived in an autocross environment, but yearly inspections are recommended. The front control arm bushings should be replaced with something stiffer than the stock floating-rubber bushing and the front ball joints should be regularly inspected for looseness – they only seem to last a couple of seasons before wearing out, which requires replacing the entire control arm. The stock rear trailing arm bushings work well, but stiffer options exist. Engine mounts are notorious for tearing in half, so stronger aftermarket replacements are highly recommended. The E46 330 has upgraded rear subframe attachment points as compared to the 2.5L cars, so it makes sense to start with one of them as aftermarket reinforcements are not legal.
That brings us to an important aspect of any competition car: spares. You’ll want some, particularly if the car will see any ProSolo action. At least one spare axle per side, axle nuts, front control arms, motor mounts and ideally, another rear differential. The E46 rear ends are very robust, but high RPM launches on sticky concrete can frag them.
Top Tips
Don't believe the hype. Brian Heitkotter showed in 2013 that the E36 chassis is far from dead. Lower weight and near-equal power are a recipe for success in DSP.
Do your own work. These are easy cars to maintain. They're well-engineered and have a strong enthusiast following, so performance parts are readily available on the used market.
Consult a pro: Sam Strano possesses a wealth of information for setting up these cars for success and will steer you in the right direction whether your starting point is an ex-Street Touring car or a stock daily driver ready to go under the knife.
