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 valvetrain 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 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.)
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 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 runout, and that the shaft endplay 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 carburetted 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 blowby, 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 valvetrain 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.
| Contributors: |
|
Erik Frank |
|
Ben Thongsai |
