Overboost problem CT20b + 3" + ST165

[evil_si]

last test was a run with no wastegate and the port to it completely open.
it still had boost .9 bar by 5000rpm,
this indicates that the factory twin scroll wastegate ports arnt up to it, even after almost doubling there size by milling and die grinding them out.

[Dell'Orto]

That doesnt seem right, there are several of us who've run CT20B's without any sort of issue without resorting to die grinding the entry port.

[SUBARUCONVERT]

are u running a non twin scroll manifold with a twin scroll turbo?

[sergei]

i'm running twin scroll manifold.

[pureadrenalin]

Dam, you got a fun one on your hands there.
Sounds like you need to give that ct20b to me

it still had boost .9 bar by 5000rpm

I would get ~10-11psi on my ct26 by ~ 5000rpm when the waste gate flapper was stuck open on one of those crappy XSpower gaskets.

[RedMist]

Sergei. How did you resolve this?

[sergei]

I have not, yet. I am still wainting for evil_si to make up some time for me.
The plan is:
make a spacer (~60mm tall) between turbo and exhaust manifold with 2 40mm pipes sticking out on each "entry" side (remember turbo is twin entry so it need 2x wastegates) and have 2 wastegates venting way before turbo.
This modification will result in turbo sitting about ~50mm lower and ~25mm closer to radiator, which result in compressor hosuing sitting very close to radiator and completely interfeering with radiator fan (which would be fixed by using a slim aftermarket unit).
I still have not decided to have the wastegates discharges to double Y into down pipe or Y into separate path (side of the bumper) due to legal issues.

[vvega]

sergei i have a ct20b(steel) and a sx power downpipe....
after a bit of panel beating im not getting any boost creap.....
i aslo ha a 1.5 meter 3" exhast system so flow is fairly um...un impeded

and thats with my dodgy attuator

i do have to ask....whats the attuator your useing off ??

v

[mister2]

Have you tried pressure testing your actuator to make sure it opens? Use a MityVac to pump it up. You see this from time to time that the diaphragm rips = over boost.

I'd be very surprised if 2x 20mm ported wastegates can't flow enough for a stock CT20b.

Generally internal wastegates are ok on most stuff and where it isn't (eg S4 RX7) they are ridiculously undersized (eg 1x 10mm hole!) - not 2x 20mm.

Cheers

Nick

[sergei]

Well, as I stated earlier, I have tried running the car without any wastegate -- 2x20mm ports venting to atmosphere, and I was still getting boost.

[vvega]

yeah ??? and
i still get boost without a attuator on mine
your still gunna get spool :S

[sergei]

Hmm, on few other cars (mainly CT9 and 12s, and VF10 hybrid) I've tried to disconnect actuator and run with it completely open, I was getting 0 boost no matter what load.... Oh and other thing I was getting almost 1bar boost without wastegate, theese things should be about 0.7bar factory with wastegate in...

[vvega]

are you getting 1.5 bar with no attuator ?
all the waste gate has to do is vent enough gas to keep boost at set point
if it wont go above .5 bar then you wastegate hole is fine

[sergei]

I was gettting almost 1bar at 5000rpm, I know for sure it would go over 1 bar very quickly if I rev higher. thats without wastegate.

[vvega]

.9 ??? by 5000 ??
wierd
i have a rc motor aand a steel wrc turbo
2x 20mm holes is a big area
si jump online and chat bout it bro...must be missing something

[vvega]

sergi you use msn ??
you have enough area to vent prolly 400 hp
id hope your not seeing 400 hp at 5000 rpm

[sergei]

vvega-> check your pm.

IO dinoed almost 180kw atw at TP, that is with very restrictive muffler...

[mister2]

Is that with the flap wired open though? With the actuator off can you open the wastegate by hand - maybe it is not opening enough and hitting on the turboxs downpipe. I'd still be pressure testing your actuator on and off the car to confirm operation. Unless your wastegate ports are obstructed - that is a pooload of wastegate area.

[vvega]

been talking to him directly
even with no down pipe and wastegte flap on there hes still getting 1 bar at 5krpm

[evil_si]

there is no wastegate flap in there, it was removed when i ported the holes out, and set it up for external.

i got sergei to unbolt the wastegate completely and go for a drive, he was getting .9 bar by 5000rpm,

the plan now is to run a spacer between manifold and turbo and run 2x externals 1 off each scroll eaxh with its own 38mm feed.