The legendary BMW 2002 was last available from the showroom floor in 1976, but even today makes for a great daily driver, enthusiast car, budget sports car, or all out track car. Not all of us can get our hands on the early lightweight 1972 or 1973 2002tii or the even more rare BMW 2002 Turbo. There are still thousands of base model 2002's out there, from 1602 to diving board bumper 1974 to 1976 cars. A lot of owners are interested in extracting more horsepower from the venerable M10 engine. This article will cover some of the basic concepts getting more horsepower from a 2002. A lot of the ideas are easy to do in the midst of a rebuild or not. The 2 liter engine in the 2002's were conservatively tuned from the factory. With the right parts and intelligent modification, the M10 engine can yield much more power with no loss of reliability or driveability.
We will break 02 modifications into two classes: Stage 1 and Stage 2. Stage 1 setups are primarily "bolt-on" and reversible mods. Carburetors, exhaust header, a mechanical advance distributor and other tuning tricks like these comprise most Stage 1 changes. Stage 2 performance mods usually affect internal engine components, such as higher compression pistons, minor head porting, and valvetrain work. Want to go further than this? Call up a reputable BMW engine builder for a track or racing engine.
How much compression should I run? Choosing a compression ratio for the 2002 engine is critical for maximizing the potential of the camshaft/cylinder head combination you choose. The compression ratio in an engine is the ratio of swept (total) displaced volume divided by the compressed volume. As this ratio increases, the overall engine efficiency increases due to an increase in the engine's Mean Effective Pressure. Essentially, this results in an increase of net work done by the engine. (more torque, horsepower!) The two primary limiting factors for a compression ratio in an engine is the type and quality of gasoline being used, and the ignition timing. For a street motor, 9 to 9.5:1 compression can be used without requiring high octane gasoline. 10:1 or 10.5:1 represents the upper limit of streetable compression ratios using nationally available 93 octane gasoline. If your 2002 runs hot in the summer, you will suffer detonation and pre-ignition symptoms (knock and ping) under high ambient heat conditions. Modern cars can run 10.5:1 compression with no problem because they have sophisticated electronic management systems that carefully monitor the engine for detonation symptoms, and retard the timing as necessary. Another general rule found from testing and experience is that higher performance cams in a 2002 really benefit from an increase in compression. For example, a Schrick 304 cam should be run using at least 10:1 compression to really make the engine come alive. Of course, the 12.5:1 compression ratio yielded by the racing pistons listed above require high octane racing gasoline.
What carburetor should I use? This response depends on the level of modification of the engine, and the horsepower increase desired. The most popular replacement carb for an otherwise stock 2002 is the trusty Weber 32/36 DGV progressive dual throat carburetor. This nice little unit is easily installed, and yields high 20's highway (25-28mpg) mileage. It will bolt right on to the stock two barrel Solex intake manifold, however, the throttle ports need to be matched up with a die grinder for optimal performance. With a stock or mild re-grind cam and headers, this application provides a noticeable increase in performance over the stock engine. This is also the only aftermarket carb legal for use in SCCA's Improved Touring class on the 2002. Hence, there is a LOT of info on this carb out there from many IT racers. There are also many shops that specialize on maximizing this carb for performance (IT) applications. Check the Roundel for sources.
The next most popular setup with a stock motor is the venerable dual 40 DCOE Weber sidedraft conversion. The DCOE Weber carburetor is a simultaneous opening twin-butterfly sidedraft design. As the model implies, the main throttle bores are 40mm. Contrary to popular belief, this is not an unreasonable setup for the street. The minor sacrifices involved with this setup are a lower fuel mileage, and some initial setup time.
A popular myth is that the DCOE's sacrifice driveability. This is simply not true. A properly jetted and synchronized set of Webers will have as much flexibility as a stock carb. These carbs should be run on the street with 34mm venturis. For baseline tuning, follow recommended jetting specifications given in a the Haynes Weber carburetor manual. It is also recommended that some sort of header/free flowing exhaust system be used, to maximize economy and performance. The best intake manifolds to use are the 2002TI sidedraft manifolds. These are well made castings (BMW - they FIT!!!), and feature a rocker shaft style setup for the throttle linkage. This linkage setup (used for the 2002TI Dual Solex PHH Sidedraft application) is factory designed, and extremely robust. Aftermarket suppliers such as Korman Autoworks and TWM Induction also offer quality linkage kits. When used in conjunction with a stock cam, DCOE Webers are legal in SCCA Street Prepared autocross competition.
Other popular carburetor conversions for the 2002 include the Weber 38/38 DGAS (a dual throat downdraft with synchronously opening 38mm throttles), the Weber 40 DFAV (also a dual throat downdraft with 40mm throttles), and various facsimiles made by other companies. These conversions yield better performance than the 32/36 carburetor.
For HOT street, and road racing drivers schools, the 45 DCOE Webers (45mm throttle bores) are considered the best choice for carburetors. They provide the best flow of all the carburetors, and mated to the proper cam, can really supply the top end performance needed in these applications. They can be used on the street, but the bottom end does suffer. 36mm venturis with 125 mains, with 50-F8 idle jets seem to work well on the track.
It should also be mentioned at this time that another performance alternative exists for sidedrafts with Mikuni. Most people believe that the Mikuni PHH sidedrafts are "copies" of the old Solex PHH sidedrafts used by the factory. This is not so. Mikuni bought out the license from Solex in the early 1970's. Since then, the carb has undergone a thorough redesign process. The only parts in common between these two carbs is the diaphragm accelerator pump arrangement. The Mikuni now resembles a cross between a Weber DCOE and a Solex. Mikuni North America offers a complete 44 PHH sidedraft kit for the 2002. Mikuni's are renowned for staying in adjustment for years. They are the "set and forget" sidedrafts. Their flow rates aren't quite as high as the Webers, which is why they're not favored by racers, and jet availability is not as good. (Mikuni North America is the primary jet supplier) The Mikuni kit does have a very high quality linkage and manifolds, which makes their installation much easier. For a street or daily driven 2002, these carburetors are well worth looking into.
One other item that should be mentioned in this section is air/fuel mixture meters. Recently, several companies like TWM Induction and Camden Industries have offered electronic air/fuel meters that utilize an oxygen sensor to monitor exhaust gas conditions. These are excellent devices to use when setting up a set of carburetors or a mechanical injection system (see below). Basically, the meter is a small "black box" with an led diode scale. The median value of the scale is the "stoichiometric" (ideal) air fuel mixture for the engine, approximately 14.7 parts of air per part of gasoline. You'll know immediately under what conditions your car is running rich or lean, and then can change jets accordingly.
What about fuel injection? If you have a 2002tii, you might want to try getting everything properly setup and adjusted before trying any performance modifications. Most tii performance problems come from distributor advance curve problems, and incorrect setting of the injection system. Beyond that, the Kugelfischer injection system can take some performance modifications with minor readjustment. The fuel delivery curve itself cannot be easily changed, but it can be shifted around to suit most needs. Higher compression pistons and a hotter cam can be used with the injection system kept intact. Extreme mods will require a custom pump recalibration, or a change to (gasp!) carburetors or a different injection system.
Alpina used to sell a multiple butterfly injection system for the tii's. This involved a 4-butterfly throttle body combined with a modified injection pump, to provide better breathing and a matching fuel delivery curve. If you can find one of these systems, consider yourself very lucky! In recent years, several companies have emerged which offer quality aftermarket fuel injection systems. The most recent and advanced models offer ignition control as well. One of the first aftermarket companies to offer a system on a large scale was Haltech. This unit, originally of Australian design featured only programmable fuel maps, and no online programming.
Today, there are several companies that make integrated injection and ignition units. Electromotive, Motec, and Haltech offer "integrated engine management systems" which are quickly rendering carburetors obsolete. Witness the awesome capabilities of any of these systems:
Closed loop control. The system constantly monitors engine
parameters like air/fuel mixture, air intake flow, various
pressures and temps, detonation, etc. The system makes
adjustments to changing conditions on the fly.
Crank triggered ignition. THE most precise way to control
the ignition sequence. Rids the engine of the distributor and its
associated nuisances.
Rev limiters andd idle speed control features, making cold
starting problems a thing of the past.
Perhaps the neatest thing about these systems is their adaptability. Because they are programmable from a laptop PC, ignition advance curves, and fuel delivery maps can be easily altered for any engine combination. Also, since these systems have the option of using a MAP sensor (Manifold Air Pressure sensor--uses speed/density relations to monitor airflow), multiple butterfly injection setups are possible. They may also utilize the more common MAF/single throttle body configuration.
Parts availability for these aftermarket systems is excellent. Primarily because they use Bosch or GM/Rochester injectors, as well as OE type sensors (throttle position, oxygen, water, oil, etc.) Both manufacturers offer injectors with MANY different flow rates and duty cycles, depending on the application. There aren't many negatives to any of these systems, with the exception of price. Like any new technology, that will drop as demand increases. These systems represent the future for grassroots enthusiasts, and they should not be overlooked.
It is also possible to adapt the fuel injection systems used on later model 320i's and 318i's for use on the 2002. The 320i used a Bosch K-Jetronic system, which is basically a mechanical system that injects fuel continuously based on air flow. The 318i used a Bosch L-Jetronic system, which is an electronic system that bases fuel delivery on air flow as well. These systems can be retrofitted relatively easily, and can offer performance and efficiency gains over most carburetor setups. The problem here is the difficulty in getting the systems to work with wild performance setups (bigger displacement, lots of cam overlap, etc.)
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