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Location:
Victoria
Registered:
December 2002
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Internal wastegate too small!
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Sat, 25 December 2004 10:49
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Hey guys! Just hoping for some advice on this problem.
A while ago I bought a high-flowed CT-20 off a guy from this site. I put it on my not so healthy 3T-GTE to see what it was like before I rebuilt the motor or got another one. Straight away it span up to 25psi which of course was way too much for the stock motor. I tried a couple of different actuator diaphrams and tested them off the turbo in case there was a problem there. So now i'm convinced the internal wastegate is now too small.
I've got hold of a recently rebuilt motor now and don't wanna kill and I wanna use the high-flowed CT-20 so I gotta do something.
Now I don't really want to fabricate a custom manifold (to use an external gate) just to fit a CT-20.
Do you think its possible to modify the factory manifold (i.e cut a hole in it and fit a flange) to use an external gate?
Or prehaps port the internal wastegate hole enough and mabey fit a larger flap so it flows enough to control boost?
-Rod
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I supported Toymods
Location:
Perth, Western Australia
Registered:
December 2002
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Re: Internal wastegate too small!
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Sat, 25 December 2004 11:02
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Simplest, neatest option would be to port the standard wastegate and to look into fitting a larger wastegate valve.
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Registered:
May 2002
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Re: Internal wastegate too small!
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Sat, 25 December 2004 11:03
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Or prehaps port the internal wastegate hole enough and mabey fit a larger flap so it flows enough to control boost?
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This is what I did with a high flowed T28 (the baby size one 0.48 A/R exhaust housing) and it worked a treat. I previously had issues with boost creep (it would just keep climbing with rpm). Mine was not remedied with actuator changes either.
Boost control on mine now is perfect. It will hold what ever boost I set, rock solid!!
It's a cheaper option too.
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I supported Toymods
Location:
Perth, WA
Registered:
May 2003
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Re: Internal wastegate too small!
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Sat, 25 December 2004 11:31
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or you could convert your manifold to run an atmo venting external wastegate 
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Internal wastegate too small!
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Sat, 25 December 2004 12:38
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Does it seem to just hit 25 straight up, bang? Or does it rise in a believable way?
First of all, run it with the actuator rod pulled off so the gate is permanently open, and see what happens. If this reveals nothing (won't start boosting), experiment with tying it partly open in different positions with a piece of wire. You should be able to work out what the issue is by playing around like this, and if it is insufficient flow, time to attack the hole with the grinder, and stick a bigger flap on there.
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Location:
On your mum!
Registered:
May 2002
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Re: Internal wastegate too small!
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Sun, 26 December 2004 00:41
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I will be inclined to go with mrshin here - it is too easy for the flapper valve to be caught on something which is holding it from opening. I don't see a comp wheel big enough fitting in the CT20 housing to be completely beyond the stock wastegate's ability to control it to some degree.
I used to completely block (fuel line clamp) the wastegate signal with my stock CT20 and it didn't go much beyond about 18psi.
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Location:
Victoria
Registered:
December 2002
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Re: Internal wastegate too small!
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Sun, 26 December 2004 03:52
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Boost rises beliveably comes up pretty quick though, but not like when the diapram hose is disconected or anything!
Yeah I thought that the valve may have been sticking but pumping the diaphram up with a hand pump showed that to be fine. Didn't do it hot though maybe it sticks when expanded...
Compared to my standard CT-20 the compressor wheel is a lot larger (the housing has been taken out a fair bit and the turbine wheel is slightly smaller. I'll take some pics of both side by side a bit later and put them up.
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Location:
Victoria
Registered:
December 2002
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Re: Internal wastegate too small!
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Sun, 26 December 2004 03:52
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Boost rises beliveably comes up pretty quick though, but not like when the diapram hose is disconected or anything!
Yeah I thought that the valve may have been sticking but pumping the diaphram up with a hand pump showed that to be fine. Didn't do it hot though maybe it sticks when expanded...
Compared to my standard CT-20 the compressor wheel is a lot larger (the housing has been taken out a fair bit and the turbine wheel is slightly smaller. I'll take some pics of both side by side a bit later and put them up.
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Location:
Victoria
Registered:
December 2002
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Re: Internal wastegate too small!
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Sun, 26 December 2004 03:56
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Whoops! 
ke382TG How much did you have to take the hole out?
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Location:
Victoria
Registered:
December 2002
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Re: Internal wastegate too small!
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Mon, 27 December 2004 05:31
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Okay, here a couple of pics. The turbo from my original 3T-GTE is on the left, and high flowed one on the right. The wastegate flap is around 2.5 to 3 mm larger all round than the hole so I don't know if I can enlarge the hole to flow enough without changing the flap. Could I replace it with something other than one off a larger turbo? ie are they made from some special alloy? Or can I just use a chunk of mild steel?
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Location:
Brisbane
Registered:
May 2002
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Re: Internal wastegate too small!
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Mon, 27 December 2004 07:51
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A fair few ppl have mentioned fitting bigger wastegate flaps, so I'm guessing thats the way to go...why not ask an turbo rebuilder, if they have one (I wounder what the other guys used?)? I'd go for a proper turbo one, I think it'd be easier to fit and what not (save reinventing the wheel..)
Cheers
Wilbo
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