Purpose of a modified blow-off valve and wastegate
08-29-2005, 10:23 PM
#1
Instructor
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Purpose of a modified blow-off valve and wastegate
Not really sure all of these turbo terms, but what is the purpose of a modified wastegate-where is this? Same"?" with the blow off valve?
08-29-2005, 11:25 PM
#2
The wastegate regulates the turbo by letting some exhaust gasses bypass it. The wastegate operates off a spring inside it, if that spring wears out, it will let too much gas get by it, thus reducing the effectiveness of the turbo.
A blowoff valve is on the intake side of the turbo and keeps the turbo from overboosting while you're shifting or letting off the throttle. Without it you would blow up your intake manifold or intercooler pipes.
http://auto.howstuffworks.com/turbo.htm
A blowoff valve is on the intake side of the turbo and keeps the turbo from overboosting while you're shifting or letting off the throttle. Without it you would blow up your intake manifold or intercooler pipes.
http://auto.howstuffworks.com/turbo.htm
08-30-2005, 02:15 AM
#3
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I don't think it will blow up your intake!
some rally cars don't use them to keep the turbo spooled.
of course they don't care about the turbo's longevity
I think the buick grand national also never used one.
it's to stop 'compressor surge':
Compressor Surge:Typically, surge occurs immediately after the throttle plate is closed while the turbocharger is spinning rapidly, such as between shifts or when decelerating. During surge, air pressure increases between the throttle body and the compressor, which reduces the air flow at the compressor. If the air flow falls below a certain point, the compressor wheel (the impeller) looses its "grip" on the air. Consequently, the air in the compressor stops being propelled forward by the impeller and is simply spinning around with the wheel, which is still being rotated by the exhaust gas passing through the turbine section. When this happens, the pressure build-up at the discharge opening forces air back through the impeller causing a reversal of air flow through the compressor. As the back pressure eventually decreases, the impeller again begins to function properly and air flows out of the compressor in the correct direction. This sudden air-flow reversal in the compressor can occur several times and may be heard as a repetitive "WHEw Whew whew" noise if the surge is mild to a loud banging noise when surge is severe. Surge should be prevented at all costs because it not only slows the turbocharger wheels so that they must be spooled back up again but because it can be very damaging to the bushings or bearings and seals in the center section of the turbo.
basically, to stop the reversal of air flow in the turbo.
I'm not sure what you mean by 'modified' blow off valve, maybe: what's the difference between stock and aftermarket bov's?
there are two kinds of bov's:
one that recirculates the air back into the intake system (believed to be better),
and ones that vent to atmosphere.
the theory is that venting the air out is a waste of air, already cooled air.
I've heard some say that venting it out also makes the engine run slightly rich when it vents but I've never seen it proven.
aftermarket ones are generally built to a higher quality too.
the wastegate regulates how much boost the engine gets.
the exhuast gas has to force open a valve spring, the stiffer the spring, the more pressure the exhaust needs to open the valve, the more boost the engine gets.
people replace their wastegate because the spring weakens and the engine gets less boost.
some rally cars don't use them to keep the turbo spooled.
of course they don't care about the turbo's longevity
I think the buick grand national also never used one.
it's to stop 'compressor surge':
Compressor Surge:Typically, surge occurs immediately after the throttle plate is closed while the turbocharger is spinning rapidly, such as between shifts or when decelerating. During surge, air pressure increases between the throttle body and the compressor, which reduces the air flow at the compressor. If the air flow falls below a certain point, the compressor wheel (the impeller) looses its "grip" on the air. Consequently, the air in the compressor stops being propelled forward by the impeller and is simply spinning around with the wheel, which is still being rotated by the exhaust gas passing through the turbine section. When this happens, the pressure build-up at the discharge opening forces air back through the impeller causing a reversal of air flow through the compressor. As the back pressure eventually decreases, the impeller again begins to function properly and air flows out of the compressor in the correct direction. This sudden air-flow reversal in the compressor can occur several times and may be heard as a repetitive "WHEw Whew whew" noise if the surge is mild to a loud banging noise when surge is severe. Surge should be prevented at all costs because it not only slows the turbocharger wheels so that they must be spooled back up again but because it can be very damaging to the bushings or bearings and seals in the center section of the turbo.
basically, to stop the reversal of air flow in the turbo.
I'm not sure what you mean by 'modified' blow off valve, maybe: what's the difference between stock and aftermarket bov's?
there are two kinds of bov's:
one that recirculates the air back into the intake system (believed to be better),
and ones that vent to atmosphere.
the theory is that venting the air out is a waste of air, already cooled air.
I've heard some say that venting it out also makes the engine run slightly rich when it vents but I've never seen it proven.
aftermarket ones are generally built to a higher quality too.
the wastegate regulates how much boost the engine gets.
the exhuast gas has to force open a valve spring, the stiffer the spring, the more pressure the exhaust needs to open the valve, the more boost the engine gets.
people replace their wastegate because the spring weakens and the engine gets less boost.
08-30-2005, 09:05 PM
#5
Racer
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I have a turbo xs BOV. I have played with adjusting the spring tension inside of mine. I have notice that if I put some shims in my BOV to increase the spring pressure...I hold boost longer.... If I take all the shims and lower the spring tension...my boost tends to fall off quicker....
I don't know if this holds true for everyone else..but just something I noticed...
I don't know if this holds true for everyone else..but just something I noticed...
