Twin turbo questions

[94bg5]

Hey

I got a 94 bg5 gt im just getting used to the way the sequential turbo system works, i been searching and found bits and pieces of info that help. Pretty much what i want to know is could anyone explain what the wastegates and intercooler valves etc are doing from idle upto redline, just trying to get my head around the whole valley of death thing and the switchover more than anything. Be as technical as you want, im not dumb, just a twin turbo noob.

[Bugle]

Change gear at 4000 RPM or 6999 RPM, all the rest is voodoo and guesswork...

[94bg5]

This is why i want to find out how it works, change gear at redline and i get stuck with big amount of lag... wait for it then the fun part of the secondary. My question is, why can't the primary turbo be engaged throughout the whole rev range. I guess i should have never moved on from my bc5 collection, but i kind of like my gt, its got a bit more style

[Marky]

There's a heap of in depth explanations online, there's probably one on here too actually

Short version: Below 3500ish - primary only, secondary is shut off through both exhaust (ECV, the massive big copper looking thing by drivers side turbo) and intake (a valve under the intercooler on drivers side)

When it starts to switch - the exhaust valve starts to open, the intercooler valve stays shut, and the pressure is vented straight back into the intake through that BOV looking thing - this is the dip you feel as it's spooling the second turbo up but not doing anything with it

Then exhaust valve is opened fully, the intercooler valve opens up, and the recirc is closed off - it's now running both turbos at once, hence why the exhaust note changes and things ramp up all over again

Primary turbo is running the whole time

That's pretty much all there is too it. The changeover will vary depending on throttle position - half throttle it waits ages, and if you change too early and keep foot flat you will find that nice dead spot where it doesn't bother switching back to primary only - stays on both and tries to spool them up.

[Bugle]

You should be able to change at 6999 (or 7499 in a B spec) and get the clutch out before it drops too far down the rev's and hands back to the single turbo?

My BG has a short shift but I dont recall not being able to do that with the std shift setup

[Guest]

 Bugle said:

You should be able to change at 6999 (or 7499 in a B spec) and get the clutch out before it drops too far down the rev's and hands back to the single turbo?

My BG has a short shift but I dont recall not being able to do that with the std shift setup

buy an auto and you can do that

[Guest]

buy a zero sports sequential controller and move the change over to about 5500 or so then the twin turbo really comes alive!

[Bugle]

This might help

Full article here, apologies if its a repost

http://autospeed.com/cms/title_The-Subaru-EJ20-Turbo-Guide/A_2775/article.html

[94bg5]

Thanks for the help guys, im thinking either single turbo conversion or mite just wait and do an engine/ecu swap, go the whole 9 yards

[FST4RD]

Is there no way that you can remove the ecv all together and have the exhaust gases running through both turbos right from idle, rather then just the primary turbo getting all the low down gases, then the ecv switching to both up higher?

Or will the ecu crap itself if you were to remove the ecv?

[Jord]

Yes, there are aftermarket headers that remove the ECV such as the SYMS system. Tuned length with individual runners.

[FST4RD]

If you were to just hack it out and weld some piping in it\'s place, would it just mean both turbos would spool up together, ie. No vod? Would you need to add a wastegate on to the secondary turbo? Ecu play ball?

[Jord]

Yes, no VOD between 4000-4500rpm. You swap it with VOD from 0-3500rpm No secondary WG required on stock headers its all controlled through the primary WG.

[FST4RD]

Why don\'t people do this then to their tt setups?

Sounds like their are no drawbacks?

[mattapo]

laggy, but yes can be done, kind of like a simple single turbo conversion

[D-Style]

Going back a few years ago (or more to the point a few forum meltdowns ago), a member on here replaced the ECV with a custom made butterfly type valve. He was also trying to change profile on how the valve would open. He stopped posting progress reports and never been seen since.

[FST4RD]

3500rpm isn\'t too laggy... I guess you could always put a slightly smaller primary turbo on so that the initial boost comes on a bit earlier?

[Joker]

VOD has never been that bad for me to worry bout customising stuff

the system works and if your on the track your above it anyway or around town rarely get revs up to induce it

they are cruisers not sprint cars

[Guest]

I got to thrash a blitzen rev c the other day first time Ive driven a bh. VOD is like a kick in the balls then its like it never happened. Very impressed with the hustle though guess they are 206kw atf as opposed to my wrx being 160ish. Long legs too. subarus are scary enough under the bonnet at first glance without being tt imo. Would almost own a 206kw one now was tempted before the wrx but missus didnt allow it thankfully.

[Kiwiflyboy]

Auto TT are much easier to work with when it comes to VOD. the main thing you need to do is learn where it is and how to drive around it. I really have any issues with it now as I know how the system kinda works and how to drive the car to get what I want out of it. Each revision of the BH/BE slightly changed its VOD and got much better by the time it got to REV c and D. I personally love the pull I get when I want to pass with the two turbos blasting away and then being able to just cruise with good fuel consumption. Well pretty good open road sits around 10L/100km

[FST4RD]

Don\'t get me wrong, when you\'re in 2nd or 3rd, put your foot down, primary kicks in, vod, then the secondary turbo kicks in, there\'s nothing like it, the pull, the speedo shooting up, the noise, the fact that my tt legacy is probably the fastest car I\'ve driven above 100k.

Just sucks when you\'re not watching properly, change gear slightly too soon and the revs drop into the vod zone...

[Bugle]

Thats why I like the TT, you have to \'drive\' it rather than just throwing your foot to the floor and holding on (and the look of surprise on peoples faces when a 20 yr old station wagon monsters them in the passing lane)