Tomei Powered ARMS M7960 - Manual (Page 25)

RECOMMENDED SETUP FOR TURBO ENGINES
■ Using the re-circulation valve type (Blow off valve) recommendation.
The re-circulation valve is also known as a "blow off valve", but the “Re-circulation valve” type is most
common with standard setup from factory on most turbo powered cars of recent years. This part is required
when the engine is using an AFM (Air Flow Meter). The air flow meters which uses the hot wire system,
is only designed to detect a one way air flow through its chamber. The sensor picks up the air flow quantity
that is sucked into the engine and transmits this data to the ECU. But when the throttle is suddenly closed
whilst still on boost, the mass compressed air is then forced to flow back up the intake, through the AFM
(Air Flow Meter) the wrong way. This then causes the AFM to pickup the wrong information and it then
cannot transmit the correct signal to the ECU. So to prevent this issue, the re-circulation valves function
recycles the air back into the intake piping for the turbo to keep the correct flow. The "vent to atmosphere"
type BOV (blow off valves) are not completely beneficial, as this design does not optimize the air flow to
the turbo. This "vent to atmosphere" design is mainly for enjoying the pressure release noise when the
user backs off the throttle. The "vent to atmosphere" type BOV can also cause erroneous readings in the
AFM readings which then makes the EMS (Engine Management System) to pickup the wrong data and it
then cannot control the engine correctly. When the throttle is suddenly closed, the extra air flow through the
AFM can cause the ECU to be confused and numerous problems can arise. Some examples are, the engine
can run rich, fouling the spark plugs pre-maturely, or gives the wrong valve timing and so on. In addition,
when aftermarket cams are used on the engine, the overlap time can increase much more. This can make
the idling quality deteriorate in comparison with the usual timing, at high engine speeds at the worse
case scenario; it can cause terminal engine failure if a re-circulation valve type BOV is not used.
When the goes from WOT (Wide Open Throttle) to fully closed,
the high volume of compressed air in the intake piping then
flows backward. This unnatural reverse flow then causes
erroneous readings in the air flow meters sensor(s), which then
When there is no re-circulation valve
Turbo Charger
IN EX
Air Flow
Meter
Throttle Valve
erroneous readings in the air flow meters sensor(s), which then
causes problems.
From wide open throttle to fully closed, the mass air is sucked back and re-cycled in the correct flow pattern.
Then the air flow meter will have the correct reading of less air flow being sucked into the engine, and the
ECU can correctly adjust the right fuel burn ratio and timing.
25
Standard Re-Circulation Valves
Throttle Valve
Turbo Charger
IN EX
AFM Air Filter
Throttle
Valve
(Closed)
Re-Circulation
Valve
Vacuum
(Throttle off)
The excess air
generated from
the turbo
The air required
for idling