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| Introduction |
Cold Air Intake
When it comes down to earlier carbureted BMW's, a real effort was made
to pick up cold air from the front of the car. Somehow, most of this effort
was dropped when BMW came out with fuel injected models.
The early 530i's (1975-1976 models) picked up air from the passenger's
side headlight opening (this is a good pick-up point). Looking inside
the air filter housing you will see 2 large induction tubes that run parallel
to the filter housing. If you like induction sound, cut both of these
tubes out of the housing. If you don't mind a little induction noise,
cut the outlet tube out. The increased sound level will only be there
at wide open throttle. As of now, we have not tried the following but
think that it is worth doing.
On 5, 6 & 7 series BMW's, induction noise was suppressed by adding
a plastic snoot to the intake side of the air filter housing. A cold air
system could be set up by removing this snoot and running some flexible
duct tubing to the plastic cover that seals off the headlight opening.
Cut a hole in this plastic cover for the tubing. Late 6 & 7 series
BMW's had a cold air duct hole nicely formed into the plastic cover. Using
this plastic cover would give your cold air system a factory look.
On early 320i's, they also used a plastic snoot to suppress intake noise.
Remove the snoot and then run flexible ducting to the opening at the front
of the car by the upper right hand corner of the radiator. You will need
to adapt one or both ends. Another option would be to pick up cold air
under the front of the car.
Air Filters
We've tested several different air filters for flow and performance. To
date (June, '91) we sell 2 types of air filters, the MM HiFlo paper filter
and the K&N gauze filter. Both these filters have a performance advantage
over other filters and are fairly equal in performance. The K&N air
filter is serviceable and reusable. When servicing the K&N air filter,
don't overload it with oil or it can impede air flow and performance.
The K&N air filter comes pre-oiled (even though the instructions say
otherwise). The paper MM filter is about 1/3 the cost of a K&N air
filter and flows just as well. Also, a paper filter, being disposable,
is less of a mess to deal with (no cleaning & oiling).
Air
Flow Meter vs. Throttle Body
We have not measured the area of the air flow meter opening on 320i's
and compared it to the area of the throttle plate. Early model 320i's
up to 1979 use an 80 mm air flow plate in their air flow meters versus
60 mm for later 1980-on 320i's.
We have compared the air flow meters versus the throttle body opening
on L-Jetronic BMW's.
From the above, we concluded that a big throttle body available for a
325e would do very little good without increasing the size of the air
flow meter. |
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| Air Flow Meters |
K-Jetronic
When we install a 2500 HiFlo ST/Sport engine in an '80 - '83 320i, we
usually go up to an 80 mm air flow plate but this in not the air flow
meter used on earlier 320i's.
L-Jetronic & Motronic
When comparing the larger area of the air flow meter opening to that of
the throttle butterfly, it would appear that the air flow meter would
have a flow advantage over the throttle butterfly but in reality, it will
usually flow about 15% less than the throttle butterfly. For example,
a "Big Six" air flow meter flows about 495 cfm and its throttle
butterfly flows about 570 cfm (tested at 25" val/SF600). By porting
the air flow meter we have been able to increase the air flow through
the air flow meter by about 10% (540 to 550 cfm). Now, the air flow meter
is more matched to the throttle body.
Metric Mechanic can port your current air flow meter or a new one. (This
voids the warranty on a new meter.) Sorry, we'll not exchange air flow
meters. Before sending us your meter for porting, make sure your car is
running fine and the air flow meter door is not sticking. We assume NO
liability for porting an air flow meter. Please, don't send us a crapped
out air flow meter. |
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| Fuel Pressure
Regulators and Injectors, L-Jetronic & Motronic |
With Surface Turbulence™, you can put a 10% larger
engine in your fuel injected BMW without having to increase fuel delivery
to the engine. A 15% increase in engine size requires upping the fuel
pressure about 1/2 bar (7 lbs.). Going to a larger engine yet requires
a higher flow rate injector.
Regulators
Metric Mechanic offers two styles of fuel pressure regulators. The adjustable
vacuum and the non adjustable vacuum types.
Fuel Injectors
Metric Mechanic has spent a great deal of money and time flow testing
over 50 different injectors. People request this information all the time
and we do not give it out. We do sell injectors at a very reasonable cost
(to recoup R & D costs). If you're planning on installing an engine
of ours that is more than 15% larger than your current engine, you'll
need larger injectors. Due to our past experience with early HiFlo engines
we sold, we can usually figure the right injectors to use in any fuel
injection project. |
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| Fuel Injection
Manifolds |
Early
Up until 1979, all BMW's used intake manifolds with wrap around "C"
shaped runners. On BMW 2002 tii and 320i's, the manifolds were designed
in the following manner:
- The plenum log holds 2 liters (Engine volume)
- The "C" Shape manifold runners to the back of the intake
valve would hold about 500 cc (cylinder volume).
To create the broadcast power range in a BMW Engine the ram intake
volume should be equal to the cylinder volume. Looking at the above
information it is easy to see that 2 liters of intake charge will move
into the plenum log. Then this charge is moved down the ram pipes and
finally into the cylinders.
On early 6 cylinders (up to 1979), the manifold works the same.
- The plenum log holds about 3 liters.
- The intake runner to the back of the intake valve holds 465 cc.
- This ends up being an almost ideal ram manifold for a 2.8 - 3.0
liter BMW engine.
On a 3500 HiFlo Sport Engine we like to use a "C" shaped
intake runner from a 4 cylinder manifold and use it on a 6 cylinder
manifold. (See picture below.) The 4 cylinder runner holds 400 cc (versus
300 cc for a 6 cylinder) and has a straighter entry angle at the end
of the "C". Substituting a 4 cylinder runner, the intake ram
volume becomes 565 cc, which is ideal for a 3500 cc engine.
Late
Later model BMW's from 1980 on use a laid back style intake manifold.
Air has to go through fewer bends to get to the port and the entry angle
into the port is a lot straighter. These manifolds produce a cross ram
effect by choosing runners that are 180° out of phase to each other
and running them opposite to each other in the plenum chamber. These
manifolds are very well matched to the flow rate of a HiFlo Sport Head.
The manifold runners flow at 112 cfm to 116 cfm measured at 10"
vacuum. |
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| Tuning
of Fuel Injected BMW's |
K-Jetronic
For the K-Jetronic (320i & early 323i) using a HiFlo ST head or 2200
HiFlo ST Sport, install the engine and set CO.
L-Jetronic
and Motronic
For L-Jetronic/Motronic (all 6 cylinder BMW's, 318i and late 323i)
Once the engine is warmed up, fuel delivery in an L-Jetronic/Motronic
Fuel Injection system is controlled in the following way. Low speed running
(below approximately 3500 RPM) is governed by the air flow meter. Once
above 3500 RPM, if the engine is under load, the air flow meter will be
bottomed out and its resistance out put will become constant. Above 3500
RPM, fuel delivery to the engine will be fairly linear. Fuel flow will
be dictated by triggering off the injectors (through the breaking of the
ignition points and the flow rate of the injector).
So, to tune the L-Jetronic Fuel Injection System, two things have to be
done. First, the fuel delivery needs to be adjusted to achieve upper RPM
power and second, the air flow meter needs to be recalibrated for low
speed running. Tuning details are covered in the tuning guide we send
out with our engines. |
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| Fine
Tuning the Motronic Computer |
Introduction (May, 88 - Page 7)
If you have a USA or European Motronic fuel injection system and you
notice any performance problems, you may need to "fine tune"
your system by making an adjustment inside the computer box. It can
be adjusted to correct lean running (hesitation or surging), poor idle
and to eliminate pre-ignition. The duration of injection can be changed
and the timing can be retarded.
The Procedure
- The computer box is located on the interior ceiling of your glove
box.
- Remove the Phillips screws that attach the bottom cover plate (opposite
side of ID sticker). If your computer box has "bend-over tabs",
pry these tabs back and do not remove any screws.
- Remove the cover plate.
- Remove straight blade screws at the top and Phillips screws at the
bottom of the circuit board.
- Remove rubber plug in center.
- Locate on the PC board the switch used for adjusting duration of
injection and/or ignition timing. In pre '85 cars this will be a blue
switch numbered 0 - 7. In later models it’s black. On late Motronic
Systems ('87 on), the computer box has no adjustment switch.
- Use your fingers to turn the switch (see picture) or if the switch
is black use the adjusting tool described below.
- The stock USA switch setting is at "12 o'clock" (fully
counter clockwise position). Rotating the blue switch clockwise, one
notch at a time, will produce the following changes. Also included
are European Motronic computers.
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| Intriguing test
results from an '85 535i |
- Using Switch Position #1 and a K&N Air Filter increases the
1/4 mile speed by 1 mph and .4 sec. (We sell K&N air filter #33-2005.)
- Disconnecting the oxygen sensor slows down a Motronic equipped BMW
over a stock BMW by about 1.5 mph and .7 sec.
- Removing the air filter housing and eliminating the cold air pickup
costs about 2 mph and 1 second in the 1/4 mile.
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| Tuning of Fuel Injected
BMW's |
| The tuning of a HiFlo Sport Head on a 320i is as easy as setting
the CO adjustment (covered in "BMW Fuel Injection the Enlightened
Approach"). On 318i or 325e and all 6 cylinder BMW's the tuning
method we use now is to add an adjustable fuel pressure regulator and
increase the fuel pressure. We then tighten up the air flow box spring
and set the CO. We are currently looking at HiFlo Fuel Injectors. Tuning
details on HiFlo Engines are covered in our tuning guide (to be available
in June of '87). |
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