Unsteady boost on gen3 3sgte

[kim0663]

Details of the car is:
Sw20 with a gen3 3sgte with steel wheel ct20b.
Gauge is a defi unit.
3" straight pipe intake
3" chinese downpipe that I have used without any issues for the past 3 years (wg catching now all of a sudden...? hmm)
2.75" s/s exhaust
xs power i/c

Sorted out detonation issues I have had since the swap today (I think I've got them all now...) and car runs mint.

However, on WOT the car hits 1.2 bar and my boost controller isn't even turned on. That's in first and second gears, so I would assume in 4th, 5th, that boost might creep up even more.

Hitting 1.2bar doesn't worry me too much but the gauge needle flickers between 0.9 bar and 1.1~1.2 bar constantly on WOT which does worry me a bit. On the gen2 engine, it wasn't as bad and setup has remained the same (exhaust, dp etc)
Probably best to see it on video thus I'll try and get a video of the boost gauge replay...

Any ideas for the cause of boost flickering?

[sergei]

Details of the car is:
Sw20 with a gen3 3sgte with steel wheel ct20b.
Gauge is a defi unit.
3" straight pipe intake
3" chinese downpipe that I have used without any issues for the past 3 years (wg catching now all of a sudden...? hmm)
2.75" s/s exhaust
xs power i/c

Sorted out detonation issues I have had since the swap today (I think I've got them all now...) and car runs mint.

However, on WOT the car hits 1.2 bar and my boost controller isn't even turned on. That's in first and second gears, so I would assume in 4th, 5th, that boost might creep up even more.

Hitting 1.2bar doesn't worry me too much but the gauge needle flickers between 0.9 bar and 1.1~1.2 bar constantly on WOT which does worry me a bit. On the gen2 engine, it wasn't as bad and setup has remained the same (exhaust, dp etc)
Probably best to see it on video thus I'll try and get a video of the boost gauge replay...

Any ideas for the cause of boost flickering?

Same problem as I had with steel CT20b... Although I could see 2Bar easily...

viewtopic.php?t=50929
In short this is the solution that worked for me (not necessarily you have to follow that path):

[samlloyd]

Have you got an internal gate at the moment?

Can you grab the wastegate actuator arm and move the lever so you can rule out that its seized or similar?

[gt4dude]

ive been through the same bullshit on the toyota CT turbos, am still going through the same bullshit with the internal gate on a garrett gt2860rs even after having the internal gate bored out around 32mm (kinda helped got 1.0bar that creeps to 1.2 instead of 1.5bar from 4000 onwards), but am now going for a 44 or 50mm external.... i think the problem is 3rd gen 3sgte heads flow too damn good, as this turbo is supposed to bolt on to an s15 spec-R as-is to run at around 0.7bar

[sergei]

ive been through the same bullshit on the toyota CT turbos, am still going through the same bullshit with the internal gate on a garrett gt2860rs even after having the internal gate bored out around 32mm (kinda helped got 1.0bar that creeps to 1.2 instead of 1.5bar from 4000 onwards), but am now going for a 44 or 50mm external.... i think the problem is 3rd gen 3sgte heads flow too damn good, as this turbo is supposed to bolt on to an s15 spec-R as-is to run at around 0.7bar

I don't think it is to do with gen3 head. I had over boost problem with gen1 head (which is very different).

[evil_si]

We tried all sorts on Sergei's car to eliminate the overboost issue.

Including boring out the wastegate port to well over twice is original size,

Tried restricting the exhaust downpipe to drease the flow

Think there was something else but it was awhile ago so i cant remember, any ideas Sergei?

Last we did the turbo spacer with the twin wastegate ports, and it worked perfectly,

[samlloyd]

Could you have got away with 1 external waste gate, and have had the 2 pipes running into the bottom of it?

[sergei]

Could you have got away with 1 external waste gate, and have had the 2 pipes running into the bottom of it?

yes, with a separator. Would worked fine, only problem is with separator burning out. Bazda has this setup a while ago I think.

[sergei]

We tried all sorts on Sergei's car to eliminate the overboost issue.

Including boring out the wastegate port to well over twice is original size,

Tried restricting the exhaust downpipe to drease the flow

Think there was something else but it was awhile ago so i cant remember, any ideas Sergei?

Last we did the turbo spacer with the twin wastegate ports, and it worked perfectly,

First mod was grinding and hammering out XS-Power down pipe to make sure it was not catching.

As a test I completely unhooked the wastegate actuator jammed the wastegate flap wide open. Was seeing boost just like it was hooked normally.

Second mod was boring out the ports and feeding them into single external.

Third mod was restriction of the down pipe (BTW that explains why XSPower downpipe came with a gasket that had a lot smaller ID).

As a test I completely removed downpipe. I got 1 bar boost @ 5000rpm with turbo and enlarged ports venting straight into atmosphere.

I think once you are flowing past certain amount through the turbine, the factory wastegate ports stop flowing due to venturi effect.

I think this mod is partially responsible for such easy power gain (it went from 175kW to 195kW, albeit with different ECU and exhaust went up from 2.5in to 3in). The engine was otherwise stock ST165 gen1, with ST205 W/A I/C and ST205 steel turbo.

[kim0663]

Have you got an internal gate at the moment?

Can you grab the wastegate actuator arm and move the lever so you can rule out that its seized or similar?

Yeah I'll try that tomorrow... Here's to hoping!

[Al]

Hell on MR2SIK's SW20 with built gen3, the ct20b can't flow ENOUGH

[headshotnz]

@sergei

Whats the twin external wastegates for?

And 2 bar is just under 30psi right

What can the cermatic ct20bs hold?

[kim0663]

What can the cermatic ct20bs hold?

It'll hold as much boost as your wallet/balls are willing to take it

[sergei]

@sergei

Whats the twin external wastegates for?

And 2 bar is just under 30psi right

What can the cermatic ct20bs hold?

Those turbos are twin entry, to properly vent you must have two waste gates (internal waste gate is composted of two valves joined by same arm).

[headshotnz]

@sergei

Whats the twin external wastegates for?

And 2 bar is just under 30psi right

What can the cermatic ct20bs hold?

Those turbos are twin entry, to properly vent you must have two waste gates (internal waste gate is composted of two valves joined by same arm).

Ah right, cheers mate

For some one reason i had it in my mind that it was only the ct26s that were twin entry