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Blow off valves

craz0

By craz0,
in Engines & Forced Induction

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Evo_Lee Experienced

Evo_Lee

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Ant, it is all elementary...

A MAP (Manifold Air Pressure, also known some times as speed/density) system measures the pressure inside the intake, after the throttle body, and then adds fuel based on this amount of air. The air is not measured until it actually makes it into the throttle body.

A MAF (Mass Air Flow aka hot wire) systems measures the air coming into the engine at the near the beginning of the intake tract. A turbo system has several feet worth of intake plumbing. These cubic feet of air have been measured, and fuel has been added to match that amount of air.

A blow-off valve that vents to atmosphere on a system that uses a MAF causes problems with the Air/Fuel mixture, every time it is venting. Causing the cars to stumble/stutter/stall during gear changes. Following the explanation above, the blow off valve just vented all that pressure outside the intake tract. Your A/F ratio is now something like 7:1 or worse. So the car bogs from the way over-rich A/F ratio.

If you want a vent to atmosphere BOV on a MAF system, you will have to relocated the BOV further away from the throttle body or install a idling stabiliser which clamps the signal to prevent the engine stalling.

Vents to atmoshpere only.

You can buy recirculating clips for them from HKS USA, just not Japan.

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