Overboost problem CT20b + 3" + ST165

[sergei]

Hi recently I've done full 3" exhaust (from turbo, with 3" XS Power down pipe) on my ST165 with CT20b (and 185 blitz ecu).
Right now with even boost controller off it peaks boost at about 1.5-1.7Bar at full load. So far I've removed the turbo, checked operation of wastegate (with compressed air), it opens fully at ~1bar, it does not interfeer with down pipe (although wastegate valve is quiet close to the wall of the down pipe).
Right now my options are:
1) Modify down pipe in such way so it would flow more in waste gate area.
2) Custom made twin entry exhaust manifold with 2 external waste gates hangin off it.

I know option 1 would be relatively cheap compare to option 2...but question is: what is exactly at fault here - is the internal waste gate big enough?
BTW with restrictive 2.5" exhaust car made 178.8kW at the wheels (16.5psi) at torque perfomance with really funny boost curve (I assume that the problem was there before but 2.5" exhaust was not flowing enough for it to create very high spike).

BTW how much I'm looking at option 2, ball park figure. I also want to keep my W/A intercooler and turbo in "factory" position.

[Akane]

Maybe the best thing to do is go external if space is not an issue, if you are definitely sure that the wastegate assembly is not hitting the 3" dp, and this has only happened once you changed to 3" dp, then it must not be flowing enough through the internal, or as you said, the 3" dp is designed so badly that it's blocking the path of flow near the wastegated area.

If you really want to you can try a port job / dp job first, a quick home port job / dp job should see if you get any improvements. Also you can try to extend your actuator about 2-5mm's and see if your boost drops, if it doesn't then your internal w/g port might well be too small / wastegate air flow around dp is bad.

How about:

1) Port the wastegate, if it fails then
2) redesign 3" dp to have seperate pipe (divorced dp, anthonym had this on the TD06 along with routing the w/g to eliminate overboost - common problem on TD06), if it fails then
3) go external.

[flygt4]

i remember mmm boost had a similar issue when he put his on his mr2. i think it was something to do with his screamer pipe from memory.

[sergei]

It is XS Power downpipe, which I got off drivenperformance...

Here is the pic of DP:

[sergei]

I've grinded off slightly (~4mm) the posts on the turbine housing where waste gate sits, still same problem...

[Akane]

Got a better pic on the other side where the flapper is?

[Dell'Orto]

The issue with mine was, that even though the wastegate flapper had plenty of room to move, the way it was designed meant it had to do a funny curve to exit the pipe.
Kinda hard to explain, but the wastegate opening about 1/2 covered the screamer pipe when fully open.
We opened it up when we plumbed the screamer back in, and it held boost fine from then on. Seems CT20B's like lots of room to bypass exhaust gas.

[sergei]

Here are the pics of the flap area:

[sergei]

Ok, I have some dea on how to modify my down pipe, who would like to implement it with TIG and some stainless piping?
I will pay up to $250 for good job.
I'm in auckland, I can drive over in greater auckland if necessary, I can take off the down pipe and bring over if it is better (although some clearances would be tough to estimate).

My idea involves in separating waste gate flow from turbine flow and gradually joining two flows further down the stream.
This will involve in relocating oxygene sensor further down...
I post the pics up when I photoshop mokup...

[cr1mnl]

pm evil_si. hes got all the gears and skills to do it

[sergei]

Here is the mock up, and please don't make any "it looks like penis" jockes

Red Arrow points to separator (pipe, that is flared from turbine diamater to 3") that will separate turbine flow from wastegate flow.
Thats how turbo looks:

As you can see turbine outlet has gradual tapper in which the "separator" can slot it...

[SUBARUCONVERT]

why dont u just go external, problem solved

[sergei]

The problem with external => can't put anywhere except where is the stock wastegate flap (with stock item removed), can be a problem in separating flows (need custom gasket etc.).

[Al]

Amazingly the poms of all people actually have a solution for the XS powers crap build quality. Usually they just have a cry, then pay their mechanic god knows how much to fit something else.

Ok peeps and peepettes,

i've been out the back today with my new angle grinder to make some alterations to the downpipe I have.

In some of the shots you can clearly see where the problem resides.

I've tried to take as a descriptive photo as possible for the mods I've just carried out.






















Hope this is able to help others avoid the potential overboost issue that people might find with certain downpipes.

Ant

[sergei]

Thanks, I will try that today, but I'm sure that I've tried wastegate operation with turbo off the car and down pipe attached (and with wastegate fully open, to remove and install down pipe to see if it is catching)....
I will let you know the results..

[sergei]

OK, I've taken it for a ride with grinded down pipe, still same problem...

[Inane]

put it to the sword

[avinesh]

OK, I've taken it for a ride with grinded down pipe, still same problem...

is this problem only asociated with ct20b's i have the same brand down pipe on my mr2 (ct26b) an it doesnt have any over boost problems but i was goin to upgrade turbo to ct20b an wanted to know if only ct20bs have this problem with xs power dp.....

[MrOizo]

OK, I've taken it for a ride with grinded down pipe, still same problem...

Could you take it for a drive without the WG actuator arm attached?

just to see what happens?

[sergei]

Good idea, I was thinking in modifying waste gate actuator rod so it will be adjustable, but I will take the rod completly tonight and see how that goes.