Twin Turbo Preperatory Rotation, too early..

[Robbks]

Hey guys, a little background
Gen2 GT Legacy fitted with EJ20R, VF18/19 turbo combination, single wastegate setup, ported ECV, fully rebuilt solenoid box and vac hose system with new silicone vacuum lines.

I've had a problem over the last week where the preperatory rotation of the secondary turbo is triggered far too early (3000 rpm as opposed to 4000 rpm), this leaves me with ~7psi of boost and not able to make power.
the IC valve is not opening until it's usual 4200rpm.

No trouble codes from the ECU, and it pulls like a train as usual once the IC valve opens up to allow the secondary boost into the engine.
Something is triggering the ECV to open too early.
all the solenoids appear to operate correctly when in diagnostic check mode.
car has been running faultlessly for the last few months since i bought it and the entire system was re-built just prior to my purchase

anyone had a similar issue or a solution?

[Sarra]

Take it to the person who rebuilt it, and ask them if they warranty their work, or would be willing to at least help you out.

[Robbks]

All sorted,
one of the hoses inside the BBoD has a joiner in it.
that joiner had become brittle/ broken and apiece of the plastic had become lodged in one of the connectors to the outside of the box, hence the solenoid was unable to bleed off enough air to be able to control the ECV actuator properly.

Also, the painstaking process of re-building the box was done by the previous owner (whom i know well from our local Subie Club)

[Sarra]

Ah, good to see you at least identified the problem, if not fixed it. I have no idea on the workings of the TT system they used on those unique cars. ;)

[Robbks]

read this...
http://www.veloce.pwp.blueyonder.co.uk/ ... opprt2.htm (http://www.veloce.pwp.blueyonder.co.uk/Twin%20Turbo%20Operation/ttopprt2.htm)

and you'll know 300% more than most mechanics do about the TT system.. :D

The entire system works on vacuum/ boost pressure actuators and solenoids to control the operation of the actuators.
when they get old, the lines get gummed up with blow-by deposits (vacuum and boost provided by the engine obviously) and the pressures are not as high/ low as they should be, so the system operates incorrectly, causing issues such as this as well as increased VOD and sluggish return from twin to single turbo operation, basically making the thing a pig to drive.
a properly operating TT system does a damn good job for day to day commuting and a decent blast around the county.
but it's very fickle to keep operating at it's best...

[Sarra]

That is almost scary to read, how much engineering and design went into this.

It's different than the twin turbo system used on the RX-7... Though just as complicated.

[Robbks]

good thing about the RX7 is that it produces enough exhaust gas to make decent turbo's spool properly.
a 2.5 TT Subie would be much nicer to drive and less VOD issues

[Sarra]

No kidding. There was a report of a tuner in Australia tuning the VOD out of a TT motor. Now I would be interested to see how that was done...

I would rather take my rotary engine with 3 rotors, and NA, in a 1979 chassis. ;)

[Robbks]

Basically what has been done down here a number of times to help the TT's get rid of the VOD is the following (was already done to my car before i purchased)
-fit set of free flowing dump-pipes 2.5"+
-port the opening in the ECV as much as possible,
-replace all the crappy turbo outlet pipes with decent diameter silicone ones
-adjust the ECV rod slightly looser to enable the secondary turbo to pre-spool a little earlier
and finally tuning.

from the AFR logs i've seen the tuners seem to richen the fuel right up in the cells that the ECU traces through during the VOD, which appears to help reduce it further, obviously a combination of correct AFR's and timing to produce higher EGT's to promote spooling of the turbo. also, a good boost controller to shut the wastegate completely as it goes into the changeover to allow as much exhaust gas as possible to get to the secondary to spool it up.

[Sarra]

Basically what has been done down here a number of times to help the TT's get rid of the VOD is the following (was already done to my car before i purchased)
-fit set of free flowing dump-pipes 2.5"+
-port the opening in the ECV as much as possible,
-replace all the crappy turbo outlet pipes with decent diameter silicone ones
-adjust the ECV rod slightly looser to enable the secondary turbo to pre-spool a little earlier
and finally tuning.

from the AFR logs i've seen the tuners seem to richen the fuel right up in the cells that the ECU traces through during the VOD, which appears to help reduce it further, obviously a combination of correct AFR's and timing to produce higher EGT's to promote spooling of the turbo. also, a good boost controller to shut the wastegate completely as it goes into the changeover to allow as much exhaust gas as possible to get to the secondary to spool it up.

Ahh, yes, that makes sense! I bet they bump the timing up a little too with the rich bump. that's part of how I got my TD04 spooling quicker on my 2002 WRX.

Geesh, I think I want to get my hands on a TT motor and play with it. Sounds like it might be kinda fun...