the lowdown on external wastegates

[capella re]

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


looks kind of like a blow off valve (this is a tial 38mm wastegate)


this shows how a screamer pipe exits


this is your more common factory internal wastegate


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.

[gotorx7]

I'm running a Turbosmart 48mm External..

It's plumbed back in, no screamer thanks

Seems to work very well, I have adjustable boost, never creeps.

[capella re]

i also had a 48mm turbo smart wastegate, plumbed back but flanged at the end as well as the dump pipe for easy dropping of the exhaust for racing (what a waste that was with no track to race at :()
was a t04 turbo as well. had problems holding boost at 10psi and 14.5 psi with 6 psi spring using a greddy profec b spec boost controller.
replaced the spring to a 10psi one and held perfect at 10 and 14.5 psi but i would say it was the ebc at fault not the wastegate.
love the way you feel the external gate dump through the exhaust under your ass in the drivers seat-like a midget massage

[FC3S]

mines a 60mm hks copy venting to atmo holds 12 psi all day no worrys at all on a T04e/66

[FLEX]

60mm RACEONLY external gate w screamer, dont have any problems holding 10psi

doc wat sort of power are you making at that boost?

[13bwankel]

Funny this topic comes up, I'm currently deciding what to get for the 12a. Going to be running a to4E front on a modified s5 rear housing, At this stage I can stay internally gated, but think since I have to build a manifold anyway we probably should go external, I can get turbosmart through work any suggestions what size?

Ryan what was the RACEONLY one worth? any idea where I can get Tial from? I'd like to have a look at them too,

[FC3S]

on a 12a with that size turbo i would look at a 38 to 44mm gate think i put a 38mm gate on the last 12at i did and it go's HARD with a small t04 set up

mine made 280kw's on 16 psi on a very light tune (had fuel dramma's) with a t04e/t66
with boost set at 12 psi i was making around the 230ish mark on a rich safe tune
soon to b a t04Z on 20 psi hoping for around the 350kw's mark may allso b going E85

[capella re]

Originally Posted by 13bwankel

I'm currently deciding what to get for the 12a. Going to be running a to4E front on a modified s5 rear housing, At this stage I can stay internally gated, but think since I have to build a manifold anyway we probably should go external, I can get turbosmart through work any suggestions what size?
,

if your expecting to go harder in the future, like you said may as well go external now, cheaper in the long run. i would agree with doc, 38mm-44mm would do great but certainly no more than a 48mm at that level.
as far as i'm aware the waste gate size depends on the size of the turbo vs the amount of boost you want to run. so t66 running 26psi needs a larger/stronger wastegate to maintain correct boost levels than a gt28rs running 12psi. gates arent cheap so if you plan running more boost or bigger turbo, don't skimp but on the same token the tial 60mm gate was quoted as being 3 times the price as a 38mm, so dont overkill either.
ive heard good and bad about ebay copies but probably more just luck of the draw so i can't give any conclusions there.
you can get tial through capa (just tell them its for your chevy with double pumpers and rat rad 424 big block or something!)
or
http://www.skylinesaustralia.com/for...t-t306047.html
brand new tial 44mm wastegate silver .9 bar spring , all clamps and fittings and instructions included only opened box to take pictures.
$460 including express post australia wide
or local pickup in perth
these are over $600 new , so its a bargain price
Pm or email bad180sx@hotmail.com


he also has a to4z for $1300

[FLEX]

big boost=small gate
low boost=large gate

[capella re]

Originally Posted by FLEX

big boost=small gate
low boost=large gate

weird, i would have sworn it would be the other way round, but i guess when i think about it all the wrx's evo's and hondas don't exactly run monster turbo's but run like 25psi and have 38 to 44mm gates, wheres as rotors run monster turbos but more often than not don't go over 20psi (on the street) yet run 48-60mm gates. i learnt something today boys and girls, ryans smarter than i am. damn that sucks a$$!!