capella re
06-02-2010, 11:14 AM
a wastegate is a valve that diverts exhaust gases away from the spinning turbine wheel in a turbocharger. diversion of exhaust gases controls the turbine speed, which in turn regulates the rotating speed of the compressor (ie the amount of boost you run). The main job for the wastegate is to control the maximum boost pressure in a turbocharger, to protect the engine and the turbocharger from over boosting and subsequent engine and or turbo failure.
an external wastegate is a separate mechanism used with turbochargers that replaces the normally self contained internal wastegate. an external wastegate requires a specially constructed turbo manifold with a dedicated exhaust/manifold runner going to and from the wastegate. the external wastegate may be part of the exhaust housing itself in some cases. external wastegates are a far more precise way of controlling boost levels, especially in higher performance/race application. external wastegates can be much larger since there is no problem of trying to incorporate the valve or spring into the turbocharger and turbine housing. it is possible to use an external wastegate with an internally gated turbocharger. this can be achieved through a specially designed bracket that easily bolts on and restricts the movement of the actuator arm, keeping it from opening, but certainly not as common as a dedicated external wastegate for a specific turbo type. Another route involves welding the internal wastegate shut which keeps it from opening at anytime, but failure of the weld can allow it to open again (the external gate would then regulate the boost rather than build essentially unlimited boost without such an outlet.)
external wastegates generally use a valve similar to the poppet valve found in the cylinder head. however they are controlled by pneumatics 9air pressure) rather than a camshaft and open in the opposite direction. external wastegates can also use a butterfly valve, though that is far more rare.
external wastegates solve certain problems in performance applications such as boost flutter which can be due to the weaker internal wastegate not being able to hold/maintain the higher levels of boost required as effectivley and with the ability available to change the external wastegate spring quite easily say from 8psi to 10psi or even 15psi and higher you remove the need for a boost controller if only one level of boost was required.
now a screamer pipe. a screamer pipe is where the excess gas needed to bypass the engine once full desired boost is reached, so for example once you reach 10 psi your maximum setting, the wastegate opens and diverts the exhaust gas from the engine to the exhaust so as to hold maximum boost. now because this is diverted exhaust gas on a short runner that is not muffled, it is extremely loud. normally on street applications, this runner will be welded back into your exhaust pipe along with your turbo dump pie and will continue along through your muffler and out your tailpipe reasonably unnoticed. a screamer pipe is when this pipe does not rejoin with the exhaust, it simply ends shortly after being diverted away from engine and vents to atmosphere-hence why its called a screamer pipe as you now have unmuffled exhaust air coming straight off the turbo.
this screamer pipe does not activate until full boost when the wastegate opens so as long as full boost isnt reached, and the wastegate doesnt open, there will be no noise, hence why these are common on street cars. the benefits from a screamer pipe are pretty much just to pull chicks and scare the crap out of people, performance gains are next to nil compared to diverting back into your exhaust system.
this is an external wastegate
http://image.turbomagazine.com/f/8851969/0411tur_10z+mitsubishi_lancer_evolution_viii+tial_ external_wastegate.jpg
looks kind of like a blow off valve (this is a tial 38mm wastegate)
http://www.ultimate-racing.com/Products/STi/Tial38mm.jpg
this shows how a screamer pipe exits
http://t2.gstatic.com/images?q=tbn:kDyOMDI82AD1MM:http://www.myvividracing.com/gallery/displayimage.php%3Fimageid%3D3696
this is your more common factory internal wastegate
http://www.turbobygarrett.com/turbobygarrett/images/tech_center/tech_101/Internal-Wastegate.gif
H
here is very basic information. Internal wastegates are not as good because they've got mechanical linkage that hangs around the perimeter of the turbo - although slight more "compact" you can't choose too much where that linkage goes. some can only be rotated so far. additionally, internal wastegates are sealed units with internal springs. most internal wastegates are bead rolled shut to house the spring and the diaphram area needs to be disassembled to replace the spring. finding a 1 bar spring 9about 14.5 psi) in an internal gate is not unlikely.
External is preffered because not only is the evacuation port your choice of size (35, 38, 40, 42, 44, 46, 50, 60 mm+...) but you get to position where preturbo you want to put it, recirc or not recirc, and can load it with any spring of your choice. They are also less fragile (in my opinion) compared to a little tin can with a stick hanging out of it. Internal wastegates, for the most part, have very moddest flap size of aywhere from 25mm - 30mm that i've taken note of. If you have a large motor and a baby flapper, formally introduce yourself to boost creep.
dumping the wastegate gasses is dyno proven to give you a few more hp/tq and honestly is not that obnoxious. not to mention, it's only loud when you're on full boost, so when you're doing that you usually intend to be loud anyway.
if anyone else has experience in external gates post up the good or bad examples, i know flex recently went to a large external gate with his to4 conversion and is happy with the results.
an external wastegate is a separate mechanism used with turbochargers that replaces the normally self contained internal wastegate. an external wastegate requires a specially constructed turbo manifold with a dedicated exhaust/manifold runner going to and from the wastegate. the external wastegate may be part of the exhaust housing itself in some cases. external wastegates are a far more precise way of controlling boost levels, especially in higher performance/race application. external wastegates can be much larger since there is no problem of trying to incorporate the valve or spring into the turbocharger and turbine housing. it is possible to use an external wastegate with an internally gated turbocharger. this can be achieved through a specially designed bracket that easily bolts on and restricts the movement of the actuator arm, keeping it from opening, but certainly not as common as a dedicated external wastegate for a specific turbo type. Another route involves welding the internal wastegate shut which keeps it from opening at anytime, but failure of the weld can allow it to open again (the external gate would then regulate the boost rather than build essentially unlimited boost without such an outlet.)
external wastegates generally use a valve similar to the poppet valve found in the cylinder head. however they are controlled by pneumatics 9air pressure) rather than a camshaft and open in the opposite direction. external wastegates can also use a butterfly valve, though that is far more rare.
external wastegates solve certain problems in performance applications such as boost flutter which can be due to the weaker internal wastegate not being able to hold/maintain the higher levels of boost required as effectivley and with the ability available to change the external wastegate spring quite easily say from 8psi to 10psi or even 15psi and higher you remove the need for a boost controller if only one level of boost was required.
now a screamer pipe. a screamer pipe is where the excess gas needed to bypass the engine once full desired boost is reached, so for example once you reach 10 psi your maximum setting, the wastegate opens and diverts the exhaust gas from the engine to the exhaust so as to hold maximum boost. now because this is diverted exhaust gas on a short runner that is not muffled, it is extremely loud. normally on street applications, this runner will be welded back into your exhaust pipe along with your turbo dump pie and will continue along through your muffler and out your tailpipe reasonably unnoticed. a screamer pipe is when this pipe does not rejoin with the exhaust, it simply ends shortly after being diverted away from engine and vents to atmosphere-hence why its called a screamer pipe as you now have unmuffled exhaust air coming straight off the turbo.
this screamer pipe does not activate until full boost when the wastegate opens so as long as full boost isnt reached, and the wastegate doesnt open, there will be no noise, hence why these are common on street cars. the benefits from a screamer pipe are pretty much just to pull chicks and scare the crap out of people, performance gains are next to nil compared to diverting back into your exhaust system.
this is an external wastegate
http://image.turbomagazine.com/f/8851969/0411tur_10z+mitsubishi_lancer_evolution_viii+tial_ external_wastegate.jpg
looks kind of like a blow off valve (this is a tial 38mm wastegate)
http://www.ultimate-racing.com/Products/STi/Tial38mm.jpg
this shows how a screamer pipe exits
http://t2.gstatic.com/images?q=tbn:kDyOMDI82AD1MM:http://www.myvividracing.com/gallery/displayimage.php%3Fimageid%3D3696
this is your more common factory internal wastegate
http://www.turbobygarrett.com/turbobygarrett/images/tech_center/tech_101/Internal-Wastegate.gif
H
here is very basic information. Internal wastegates are not as good because they've got mechanical linkage that hangs around the perimeter of the turbo - although slight more "compact" you can't choose too much where that linkage goes. some can only be rotated so far. additionally, internal wastegates are sealed units with internal springs. most internal wastegates are bead rolled shut to house the spring and the diaphram area needs to be disassembled to replace the spring. finding a 1 bar spring 9about 14.5 psi) in an internal gate is not unlikely.
External is preffered because not only is the evacuation port your choice of size (35, 38, 40, 42, 44, 46, 50, 60 mm+...) but you get to position where preturbo you want to put it, recirc or not recirc, and can load it with any spring of your choice. They are also less fragile (in my opinion) compared to a little tin can with a stick hanging out of it. Internal wastegates, for the most part, have very moddest flap size of aywhere from 25mm - 30mm that i've taken note of. If you have a large motor and a baby flapper, formally introduce yourself to boost creep.
dumping the wastegate gasses is dyno proven to give you a few more hp/tq and honestly is not that obnoxious. not to mention, it's only loud when you're on full boost, so when you're doing that you usually intend to be loud anyway.
if anyone else has experience in external gates post up the good or bad examples, i know flex recently went to a large external gate with his to4 conversion and is happy with the results.