School me on blow off valves...
12-31-2013, 09:03 AM
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You don't want the valve open in cruise on a turbo engine as it could cause ex side load that might hurt fuel MPG and cause unwanted heat in a street car. On a cent supercharged car I would run the spring at a fairly high rate, it will make the cruising sound level lower and should lower load on the head unit. I would guess this might show up as better fuel MPG also, but I never drove one enough to check this.
Kurt
Kurt
01-01-2014, 09:54 PM
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I might be wrong, but more air is more power. I tend to believe that at just about any rpm, the blower is putting out more air than the motor can ingest, hence the quicker I close the bypass/blow off valve, the quicker I will see boost and make more power. Sure it might only be 0.5psi of boost at 1800 rpm and half throttle, but if the bypass/blow off valve were open, it might be negative 0.5psi. So if the valve closes sooner, it'll feed the motor more air, which is more part throttle power, which makes the motor feel like it's got more cubes and more torque which is what I've always wanted.
Stop and realize the compressor sides of both turbos and centrifugal superchargers are the same thing. The phyics of the compressor does not change. The only difference is in how they are driven. Furthermore the belt driven superchargers are RPM dependent and the turbos are time dependent given a certain amount of exhaust energy. The outlet of the compressor never sees below ambient so your point about engine vacuum is irrelavent. The exception of course is belt driven superchargers will climb through the map at an upward angle instead of at a constant pressure like a turbo.
So with that aside, you are correct you will have exactly a hair dryer (high flow, low pressure) until you close the valve increasing pressure the turbo sees. The difference is the time it takes to do it this way versus normally climbing through the map. A supercharger wouldnt care as its not time dependent.
So with that aside, you are correct you will have exactly a hair dryer (high flow, low pressure) until you close the valve increasing pressure the turbo sees. The difference is the time it takes to do it this way versus normally climbing through the map. A supercharger wouldnt care as its not time dependent.
