Overboost problem CT20b + 3" + ST165

[cr1mnl]

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.)

this is what i've done with my setup. removed the wastegate flapper and linkage etc, welded up the hole where the shaft passes thru the housing and then took to the housing with a mill and ported out the 2 holes and made a flange with 2 seperate areas. 1 for turbine exhaust and 1 for wastegate. made a gasket from 2mm copper sheet so the two areas are sepeated.
works well and doesnt have any problems with boost creep at 18psi.
only problem is its quite tight for space from wastegate to oil filter so i remote mounted my filter and plumbed in a cooler.

doesnt help you fix your down pipe and would be a bit of extra work but its a possible solution.

[sergei]

Got any pics?

[cr1mnl]

i'm off work at the moment but may have to go in tomorrow so i'll get some then hopefully

[sergei]

OK, with flap fully open, I get no boost till ~4500rpm then it quickly rises to over 20psi.
So from my point of view, XS-Power down pipes are of shit designed, unless CT20b has its wastegate design flawed (I doubt that).
Buyers be ware - if you are planning to use real free flowing exhaust - don't bother with XS-Power downpipes - waste of money and time - I don't even want to calculate how much time I spent removing and installing down pipe and turbo (about 10 times down pipe and ~5 times turbo)....
Really frustrating.

[avinesh]

OK, with flap fully open, I get no boost till ~4500rpm then it quickly rises to over 20psi.
So from my point of view, XS-Power down pipes are of sh*t designed, unless CT20b has its wastegate design flawed (I doubt that).
Buyers be ware - if you are planning to use real free flowing exhaust - don't bother with XS-Power downpipes - waste of money and time - I don't even want to calculate how much time I spent removing and installing down pipe and turbo (about 10 times down pipe and ~5 times turbo)....
Really frustrating.

im running a xs power with out any problems so far but it is a ct26.....

[sergei]

what exhaust do you have, do you have graph of your boost curve?
I had no problems with over boost with 2.5" exhaust, it started only happen when I freed up the flow.

[MrOizo]

might need to go to a 2" exhaust for more relaible boost.

GT4SUM on here has a ST205 with the XS Power DP and it holds steady at 1.1 Bar - he has a full through HKS system.. might restrict through the front pipe tho... dont know what the dia is for that tho....

hmmmm

[anthonym]

So from my point of view, XS-Power down pipes are of sh*t designed, unless CT20b has its wastegate design flawed (I doubt that).
Buyers be ware - if you are planning to use real free flowing exhaust - don't bother with XS-Power downpipes - waste of money and time - I don't even want to calculate how much time I spent removing and installing down pipe and turbo (about 10 times down pipe and ~5 times turbo)....
Really frustrating.

You are wrong, there is absolutely nothing wrong with the design of the XS-power downpipe and it works perfectly well with the CT20b.

Overboosting is a well known problem with internal wastegates and low backpressure exhaust systems.

[Dell'Orto]

Mine wasnt too bad, was full 3", with a bling rice cannon at the end and a 300mm long muffler in the mix, both straight through 3". The centre muffler may have given it enough back pressure to hold it steady though.

[avinesh]

what exhaust do you have, do you have graph of your boost curve?
I had no problems with over boost with 2.5" exhaust, it started only happen when I freed up the flow.

i have a 2.5 inch system with a rps n1 tip an a flexi joint.....

[sergei]

Ok, I was wrong about XS power down pipe.
What I have done (actually evil_si):
Bore out waste gate ports on the turbine to about 20mm each.
Make up new flange+gasket which separates completely turbine flow from wastegate.
Remove factory wastegate flap, weld 40mm pipe wich going to external wastegate (38mm) and back into down pipe just before lower flange.

This setup does not work. Still same problem.

I squshed the down pipe just before were waste gate flow joins the down pipe - still same problem

So I got car back to evil_si and have done a modification to how waste gate flow joins the exhaust flow, basically we have waste gate pipe (40mm) going inside of the down pipe and continuing inside for a few centimeter - this way it obstructs the turbine flow thus theoretically restricting it and making waste gate path more favourable. Well the effect is minimal and it is quiet easy to boost up to 1.4-1.5bar with 0.5bar wastegate spring. We tried different location where from the waste gate feeds boost. No difference.

So I'm sligtly pissed off, slightly puzzled as to why I get this stupid overboost problem....

Next step would be removing waste gate completely and leaving bypass to air. But I can't be stuffed doing todayt (will do it tommorow).

So any one has any ideas how to economically overcome this problem?

[Akane]

I'm sure one day you'll find out, it'll be so simple and stupid, like "Oh damn, the vac/boost line wasen't even hooked up properly, it wasen't seeing any boost!"

[sergei]

Well we tryed from 2 different places (before intercooler and after) no effect.

[sergei]

I removed waste gate completely, the bypass was going to atmosphere, still got boost (0.9bar @ 5000rpm). .

I don't know what to do....

[Mr Revhead]

where are you taking ya boost measurement from?
cant recall if its been mentioned, but is your gauge good?

[sergei]

Tried from turbo itself - where stock wastegate feeds, also tried after intercooler. Defently problem is not in that - because I drove without waste gate - just pipe sticking to air and it still over boost - it should of been 0 boost .

Also boost guage is apexi item, and boost cotnroller backs up as boost guage as well (with peak hold function). right now boost controller is not connected to waste gate and just works as second boost guage. both of them are in bars and give out same result. Also I know it is overboosting because ECU goes into 'safe' mode after 1.4Bars - it retards ingintion and dumps fuel - car actually feels much faster on 1.3 than on 1.4bars...

[Mr Revhead]

magical boost gremlin hiding in the tvis manifold?

i was thinking along the lines of a stuck tvis causing a blockage in the inlet casuing a false reading in the manifold.

[sergei]

magical boost gremlin hiding in the tvis manifold?

i was thinking along the lines of a stuck tvis causing a blockage in the inlet casuing a false reading in the manifold.

There is no TVIS... buterflies are gone, holes filled, sandwitch plate grinded to match the manifold.

[Dell'Orto]

Plumb the wastegate into the exhaust and jam a bung in it...that'll tell you if its the lack of restriction thats causing it

[Mr Revhead]

how about a quick run with no downpipe at all.. thatll tell you if thats the issue or not