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Unusual Boost Control Issue

Davets

By Davets,
in Engines & Forced Induction

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Davets Apprentice

Davets

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Hey, 

I've had an issue with an IWG EFR turbo for about 1 year now ... I'm unable to hold anything much above spring pressure in the top end (above 6000 rpm). I've tried 3 port (with a variety of restrictors) and 4 port boost control ... 3 port gave spring pressure (@ max DC), 4 port I can manage another ~6 psi on top... nowhere near what I would expect. I've looked at WG actuator rod alignment, which is not perfect (had to machine some spacers) but seems to be an unlikely cause.

Going a larger spring works (I've tried up to 24 psi) but it's for a S15 which struggles for traction in lower gears (needs boost by gear). 

Has anyone seen this before? Or can it be considered typical behaviour and I should just tune around it?

Any advice would be much appreciated.

Current Build:  SR20 + VE head + EFR 7163 TS + Twin Port Turbosmart WG actuator + 3inch Exhaust

 

 

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Davets Apprentice

Davets

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Sure you have the turbosmart plumbed correctly? How is it controlled - by your aftermarket ECU?

Yep, Turbosmart actuator was plumbed following the image below for 4 port testing. Boost control seems to work fine at lower RPMs... so I don't think its the plumbing. I'm using a Haltech Platinum Pro for the ECU. 

Its behaving like it has really high back pressure, I can use normal duty cycles (~20%) at lower RPMs (0-4000) but I have to quickly ramp in a lot of DC at rpm increases (e.g. 65%). If I use >65% DC at higher RPMs boost quickly jumps from ~16 psi to ~30 psi (probably maxing out turbo) as I move out of the linear range for the MAC valve. 

Ba8CDQiy65gparux2qtkn4wBpFhTWDrMzvToqcN7Nu0P_Eve4Fv1TUtzaoIofg9RpWILwNZSa21H6-hs7tlynSo8YysbMeYPbR5PL2rXE9_aDnR6LIgx2mBromzWo6XtCFXB1aeJ

 

 

 

Edited by Davets
Davets Apprentice

Davets

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Drill & tap a sense port for a boost gauge on the ex manifold and find out?

Yeah good call probably something I'll investigate in the future, but I'm a little worried about introducing a leak. From what I've read, unless something is seriously wrong, backpressure should not be an issue given this setup + boost level... BW MatchBot predicts an EMAP of 29psi@7000rpm with 20psi boost.

KiwiRS4T Grand Master

KiwiRS4T

Posted
Posted
5 hours ago, Davets said:

Yep, Turbosmart actuator was plumbed following the image below for 4 port testing. Boost control seems to work fine at lower RPMs... so I don't think its the plumbing. I'm using a Haltech Platinum Pro for the ECU. 

Its behaving like it has really high back pressure, I can use normal duty cycles (~20%) at lower RPMs (0-4000) but I have to quickly ramp in a lot of DC at rpm increases (e.g. 65%). If I use >65% DC at higher RPMs boost quickly jumps from ~16 psi to ~30 psi (probably maxing out turbo) as I move out of the linear range for the MAC valve. 

Ba8CDQiy65gparux2qtkn4wBpFhTWDrMzvToqcN7Nu0P_Eve4Fv1TUtzaoIofg9RpWILwNZSa21H6-hs7tlynSo8YysbMeYPbR5PL2rXE9_aDnR6LIgx2mBromzWo6XtCFXB1aeJ

 

 

 

You say if you increase the duty cycle past 65% boost will go to 30 psi. Is this not the result that you want? As you go past 4000rpm there will be a huge increase in the pressure on the w/g to open and therefore will require a corresponding increase in the pressure to hold the w/g shut.

Davets Apprentice

Davets

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You say if you increase the duty cycle past 65% boost will go to 30 psi. Is this not the result that you want? As you go past 4000rpm there will be a huge increase in the pressure on the w/g to open and therefore will require a corresponding increase in the pressure to hold the w/g shut.

With 4 port control it can hit 30 psi with 70% DC but it's not controllable / consistent as small changes in DC results in massive changes in boost pressure (can't hit the pressures between 16 and 30 psi). I believe this instability is fairly standard behaviour for 4 ports.

Sounds like an EMAP sensor should be the next move...

 

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Davets Apprentice

Davets

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Do you have any specs on the boost control solenoid you are using?   What frequency are you controlling it at?

Both 3 port and 4 port soleniods are Turbosmart eBoost2 MAC valves, which don't seem to have full MAC part numbers on them...  I'm driving both via a DPO on a Haltech IO expander box @20-30 Hz. Pretty sure this is the 4 port. Are turbosmart solenoids driven differently? 

robbo_rb180 Grand Master

robbo_rb180

Posted
Posted

How have you set up your wastegate duty cycle and boost target maps? 

Does it start high and tapper down? Also depends what duty cycle is set at, had similar issues a while ago with a wrx with efr7670

Davets Apprentice

Davets

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How have you set up your wastegate duty cycle and boost target maps? 

Does it start high and tapper down? Also depends what duty cycle is set at, had similar issues a while ago with a wrx with efr7670

Duty cycle starts at 20% then tapers up with rpm.

I've attached a log when I was using 4 port and 7 psi WG spring. Boost is 17 psi at peak (4200 rpm, 20% DC) then tapers down to 12.8psi (6500 rpm, 45% DC). 

unnamed.thumb.png.ef1f90439d98dfcef0775fdca0a679dd.png

Edited by Davets
Ben C34 Grand Master

Ben C34

Posted
Posted
33 minutes ago, Davets said:

Duty cycle starts at 20% then tapers up with rpm.

I've attached a log when I was using 4 port and 7 psi WG spring. Boost is 17 psi at peak (4200 rpm, 20% DC) then tapers down to 12.8psi (6500 rpm, 45% DC). 

unnamed.thumb.png.ef1f90439d98dfcef0775fdca0a679dd.png

what happens with no closed loop control, just a set duty cycle?

it looks like you are getting the opposite result to expected.

Davets Apprentice

Davets

Posted
  • Author
Posted (edited)
2 hours ago, Ben C34 said:

what happens with no closed loop control, just a set duty cycle?

it looks like you are getting the opposite result to expected.

Here's two logs both with 4 port and 10 psi WG spring. Top one is with constant 20% DC, bottom one has 30%. The 30% DC run got another 4-5 psi at peak boost, but only 2 psi at the end of the run. 

unnamed (1).png

Edited by Davets

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