This article attempts to cover some of the basics of extracting more horsepower from a BMW 2002. It is provided simply as information which may be applied when considering the rebuild of a BMW 2002 or any other 2 liter BMW based on the M10 engine block.
The BMW 2002 left Munich in a rather conservative state of tune; by intelligently applying known methods and parts combinations, its power-plant can reach much higher horsepower levels, with no loss of reliability or drivability. The average enthusiast may not know what options he or she has when assembling a new power-plant. This article will try to provide guidance, and help dispel general myths about performance parts.
- What does “Stage 1” and “Stage 2” Imply?
- How much compression should I run?
- What carburetor should I use?
- What about fuel injection?
- Which cam is for me?
- Tips for Extracting More Reliable Performance From a BMW 2002
Tips For Increasing Horsepower
What does “Stage 1” and “Stage 2” Imply?
These terms refer to the level of modifications on the engine. Typically a Stage 1 setup is primarily a “bolt-on” setup. Carburetors, exhaust header, a mechanical advance distributor and other “accessories” like these comprise this level. A Stage 2 setup typically means that the internal engine components are changed. This means the addition of higher compression pistons, minor head porting, and valve-train work. Anything beyond Stage 2 is usually classified as a race engine. Note: these are totally arbitrary classifications, based on general trends. Race engines may fall under any of these, depending on the sanctioning body’s rules.
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 street-able 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 carburetor 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 (25-28 mpg) 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 after-market 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 side-draft 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 drivability. 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. After-market 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 BMW 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 re-calibration, 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 and 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.)
Which cam is for me?
Here is where careful research is necessary. Selecting the right cam for a 2002 depends on the intended application, and what rpm range you want the motor to make horsepower. 2002 cylinder heads contain large amounts of horsepower potential. Just by changing cams, improving the induction system, and running an OEM exhaust, 150 horsepower on an otherwise stock head (no porting) and bottom end is not uncommon.
The stock cam found on almost all 2002’s (with the exception of the 49-state ’76 2002) is referred to as having a 264 degree duration. This cam is a reasonable compromise between low-end torque and mid to high-end power. Also available from BMW is (was) the “sport” camshaft, with a 300 degree duration. This cam was designed for the TI’s and TI/SA’s (with dual sidedraft carburetors), and requires enlarged cam bearing journals.
The most well known aftermarket BMW cam manufacturer is Schrick. These are German cams made from new chill cast billets. Because Schrick cams are so widely used in BMW 4 cylinders, a brief description of the available grinds is given below. All grinds are referred to by their “advertised” duration number. This number is different from the “actual” duration of the cam, the amount of time in crankshaft degrees that the cam holds the valve open.
- 284 really only a mild improvement over stock, has good low end torque characteristics, no loss of driveability. Works well in conjunction with a 32/36 Weber DGV carburetor. Valve lift: 9.m intake; 7.2mm exhaust. ( a good stock replacement cam)
- 292 Probably the best overall street cam. Works well with either a 32/36 Weber or sidedraft DCOE’s. Excellent mid range (3500-5500 rpm) performance. Power gains are seen throughout the rpm range, and the top end really benefits from the breathing capabilities of the DCOE’s. This cam will yield 140-150 horsepower with accurately jetted DCOE carbs. Low end is still very impressive. Valve lift: 10.m intake; 7.6mm exhaust.
- 304 This is where the Schrick grinds start to get serious. This cam can be run on the street, but it is not for everybody. Low end begins to diminish, due to this cam’s increased valve overlap. This cam really works well with 45 DCOE sidedrafts, and a BIG ( > 2.5″) exhaust system. the power curve really begins at 4000 rpm, and continues on through 7000 rpm.
- 316 This cam is really suited only for the racetrack. The valve timing and duration are such that the fattest part of the horsepower curve is near 5000 rpm. This cam has been recently upgraded to provide the same lift figures as the 336 grind. Useful power is 4500-8000 rpm depending on carb jetting. (11.9mm intake valve lift)
- 336 This is the ultimate statement in Schrick cams. This cam has found homes in 220+ horsepower GT-3 racers here and in the saloon car series over in Europe. Only included here for informational purposes, a motor with this cam will hardly IDLE, and will easily rev to over 8500 rpm!
There are many other options for BMW cams. Re-grinds and new billets are available from various race shops, and several reputable manufacturers and tuners such as Iskenderian, and Korman. Korman offers their own version of a “300 degree” camshaft at considerable savings to versus a Schrick cam. Norris used to grind good hot cams, but they are no longer around. The best thing to do when looking beyond a Schrick is to work closely with someone who has had measurable experience in this field.
Tips for extracting more reliable performance from a BMW 2002
A “tii” full mechanical advance distributor (008 Bosch) is a nice addition, but not necessary. This distributor features only a centrifugal advance mechanism, no vacuum mechanism. This distributor has an advance curve that cuts in slowly and maxes out with a relatively small total advance. In other words, it is ideal for motors running high compression (you don’t want a quick advance curve, it would promote knock). Using this distributor on an otherwise stock non-tii motor can actually hurt performance. Cars with low compression and/or EGR need a quicker and taller advance curve to improve midrange torque and top end power. In actuality, every 2002 distributor is mechanical advance, but there is an additional vacuum assist servo which can either add advance under load, or retard the timing at idle, depending on the specific distributor. These distributors can be easily re-curved using different advance springs and weights, a variable speed drill-press, and a tachometer.
The total advance of a distributor is a function of the initial advance setting (what you set with the timing light) and the amount of advance built into the distributor itself. The main thing on any distributor, is to make sure that the advance mechanism is in good working order, that the distributor shaft has no “wobble” or run-out, and that the shaft end-play is less than .006″. It is also important to check that you are getting full total advance from the distributor. Many times, complaints about poor performance come from the fact that the distributor becomes worn or sticky and will not give full advance at the top end, hindering power.
- Convert to an electronic ignition system. Electronic ignition systems are a wonderful replacement for the sloppy breaker points setup. It often makes a noticeable difference in top end power (mainly because it maintains proper dwell/spark energy/ignition timing at high revs), and adds tremendous precision and reliability to the ignition system. On a race car with a 300+ degree cam, and 45 DCOE Webers, the addition of a common small electronic system was worth another 500 rpm on the top end. Another widely used ignition system conversion is the capacitive discharge type. These systems typically can be fired with either points, or a magnetic/optical pickup. There are several excellent brands, which yield nice improvements in performance. Capacitive discharge (CDI) systems offer a higher voltage spark (useful when cylinder pressure and rpm numbers are high), and more precise control than standard systems. The increase in spark voltage comes tends to come with a decrease in spark duration, though. CDI systems tend to be most useful in situations where rich mixture and plug fouling are problems, and a high voltage is needed to get a spark going. The leaner fuel mixtures on newer cars tend to favor a longer duration spark for a more efficient burn.
Another ignition alternative is to adapt a Bosch TCI system from a newer car. This requires a few modifications though, and is best left to those wanting to tinker. Either way, an electronic ignition system improves the precision of the ignition system, rids the system of points, and can provide higher spark energy when combined with a bigger coil.
- If you’re running a downdraft carburetor with manifold, matching the ports on the manifold to the ports on the head will improve performance as well. The stock port castings on the intake manifold are considerably smaller than the ports in the head. Opening the ports up will help breathing. Remember that SCCA Street Prepared rules state that intake ports on the cylinder head may be matched ported only up to one inch from the port entrance.
- A tii exhaust manifold flows quite well, and is a good alternative to headers. They last a long time, and are quiet. Also, Original BMW exhaust systems flow a lot better and are quieter than exhaust systems from the local quickie muffler shop. A 2002 Turbo system might be considered for engines producing over 150HP.
- If you have a ’74-’76 carbureted 2002, you might want to upgrade the clutch for any high-performance applications. These models use a 215mm clutch, whereas the earlier ones and the tii use a 228mm clutch. Changing over requires a different flywheel, clutch disc, pressure plate, throwout bearing, and the earlier longer flywheel bolts. Fichtel and Sachs (F&S) make several “sport” and competition pressure plates for the 2002 that are well suited in high horsepower applications. Also, Tilton makes an aluminum flywheel and accompanying pressure plate setup for the 2002.
- When performing a total engine rebuild, ALWAYS balance the entire bottom end rotating assembly. This includes the pulleys, crank, rods, pistons, flywheel, and clutch assembly. This is crucial when building a reliable, smooth running, high rpm powerplant.
- Pay careful attention to casting marks on rocker arms. These are potential problem areas on these parts. The rough edges cause stress risers along the surface of the part. The most critical area is actually on the BOTTOM of the rocker arm. The top surface (the edge that you see) is actually in compression under loading, and is therefore not as critical. Many engine builders like to “polish” this side. This is fine, but they often forget the much more important underside, where most of stress concentration occurs. Several performance outlets (Korman, Metric Mechanic, etc) offer special racing rocker arm which feature a stronger alloy, and hardened wear pads.
- Total seal piston rings (or other gapless designs) work excellently on all piston applications, and are worth the extra money. Your motor will last longer, have less blow-by, and make more horsepower.
- When installing a 292 or 304 Schrick cam, it is recommended to also install the Schrick heavy duty single valve springs. These feature a higher seat pressure, and will provide an extra measure of insurance. They don’t measurably increase camshaft or rocker arm wear, either. For the radical cams, double (inner and outer) valve springs are a must. Some people run double valve springs on the 304 Schrick cam. This is not necessary, and will result in accelerated valve-train wear.
- Don’t forget the cooling system. 2002’s have a tendency to run warm stock, increasing power will only increase the problem. Consider a high-efficiency re-cored radiator, a 320i radiator, or several other options (such as the Ford Pinto radiator or Volvo 240 radiator). Lower temperature thermostats are also available, in 71 deg C and 75 deg C varieties (stock is 80 deg C). It is also recommended that the stock plastic engine fan be removed and an aftermarket electric unit be installed. In the past, problems have occurred with the stock fan causing water pump failures at high RPMs, because of thrust loads imparted on the pump shaft by the fan. Electric fans do a sufficient job of cooling at speeds under fifteen mph. (and they’re quieter) At speeds over fifteen mph, airflow from the car being in motion is sufficient to cool the engine.
- While this is by no means the “complete” story we hope that we have provided a sufficient view of some typical combinations, and popular modifications that enthusiasts like ourselves often do to our own 2002’s. If done correctly and intelligently, many of these modifications to a 2002 will make it an even more “spirited” automobile, and enhance its value. In order to keep the length of this FAQ down to sub-novel, we omitted much of the “technical” discussion dealing with the building an actual engine. We did not address any of the issues associated with the M10 bottom end (crank, rods, block, etc.) Look for additions such as these in a later FAQ.
- Many of these modifications may not be emissions-legal in many states. We assume that you have researched the laws pertaining to the area in which you live and operate your car before attempting any of the modifications listed above. We do not assume any responsibility for any non-compliance you may encounter after performing any of the above modifications. In other words, try the above listed ideas and modifications at your own risk. Also, please keep in mind that we all have to breathe — when modifying your car, try to keep it running cleanly, it can be done.
Authors: Erik Frank and Ben Thongsai