ECM BB100, Instruction Manual, Page: 10 / 37

Installing the BB100
Figure 1a shows a typical “closed crankcase” PCV (positive crankcase ventilation) system.
Note that the blow-by is sucked into the intake manifold of the engine.
Figure 2a shows a typical “open crankcase” road draft system.
Figures 1b and 2b show how the BB100 is used with each system. Note that the PCV system
in Figure 1a is “opened” for the blow-by measurement. If the system is not opened, the
measurement will be more a function of throttle position than actual blow-by.
Blow-by is a pulsating flow with some reverse flow (ie. reversion). The net flow is out of the
crankcase, but for a portion of the pulsation expelled blow-by is drawn back into the
crankcase. The following conditions accentuate reversion:
•
Low engine speed.
•
Low number of cylinders (ie. a 4 cylinder engine will have more reversion than an 8
cylinder engine).
•
Small crankcase volume.
The BB100 is optimized to measure flow in one direction, so to ensure that flow will only
pass through the meter in one direction, a damping tank should be placed upstream of the
meter. A damping tank of fifteen gallons is sufficient for most engines. There is no problem
with using a larger tank but a smaller tank will cause the meter to report a higher flowrate
than actual.
The BB100 has small integral damping tanks and ECM has found that with 10’ of ¾” hose
separating the engine from the BB100, no damping tank was required for a 5.7L V8 engine,
even at idle. With a 2L L4 (straight 4-cylinder engine), a 15 gallon tank was required (Note:
with a 10 gallon tank, there was a 1% error). Since the damping tank is not under any
significant pressure or vacuum, it can be made out of plastic.
One simple method for determining the minimum tank volume required is to start with a
large damping tank and to remove most of the internal volume by filling the tank almost full
of water. Idle the engine and measure the blow-by. Then let 25% of the water out of the
tank and measure the blow-by again. If the blow-by decreases then let another 25% out and
try again. Stop when the blow-by reaches a minimum value. The volume of the tank not
occupied by water is the minimum damping volume required.
In place of a damping tank, a small muffler can be placed inline and upstream of the meter to
eliminate reversion. ECM has found that a lawnmower muffler was equivalent to a 15 gallon
tank in eliminating reversion in the before-mentioned L4 engine. The backpressure effects of
the muffler should be considered. However, in the case of the L4, the backpressure due to
the muffler was less than an inch of water. The muffler technique may be preferential for in-
vehicle measurements where space for a damping tank is limited.
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