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G'day.

Ive been around the forums looking, and all ive seen
is 2nd hand hate for the subaru TT setup?
all the numbers seems to make it an awseome choice.

does anyone have any first hand opinions on it?

can the setup be simplified?

cheers

I think you'll find that the hate for the twin turbos comes from the difficulty in modifying the turbos for more performance.

I'm sure if you are happy with the twin turbo factory performance then you'll be right with a twin turbo conversion.

Also speak to Andrew T and Fatz as they shoved the TTs into their L series wagons

Cheers

Bennie

The problem is the slight pause in acceleration (known as the Valley of Death or VOD)

It happens around 4500rpm when the engine goes from single turbo to twin turbo mode.




Id love to have a drive of one, just to see if the VOD is as bad as they say.

wow, is that because its electronically controlled?
what if they were used in a traditional way?
one boost controller, not 2?

it can be fiixed with a number of computer gear. motec and the like.

you can get enough power out of it for anything its just how you do it, if you want to go 4wd then set them up to create the torque low down, smaller turbines for better low range talk. in the same sense for 4wd why would you need tt??

for on the road and for getting major power the first thing id do with a second hand twin turbo engine would be to rip the turbos off and replace them with new ones or rebuilt ones, set the second stage one with a small exhaust turbo and a large intact turbine.

Well the tune and boost control would seem to be an issue,
I've seen the size of the turbos and Tt has been
something I'm interested in, at least eventually.
I'm looking for the most linear constant torgue I can,
not just a huge kw number

I'd be interested in using left over parts from a single
conversion

I have the 2002 Twin Turbo B4 Liberty with the Triptronic Auto in it and it has a Cold Air Intake and a RSK ECU and everything else is stock and I notice a slight drop in torque during the x-over but nothing too serious. I like the feel of pull it has. I have a few turboed Subies like an Aussie 1993 RS Turbo Liberty and a JDM 1998 22B and I like the B4 for ease of drive

The EJ20TT is a great base for more work and I remember guys in Japan that were doing really awesome work. Just search the web

Well, I owned & drove a EJ20 Twin Turbo powered Liberty for 7 years(just sold it) so here is my rundown...

The frontcut I bought was a MY97 GTB BG5 Legacy variant. I too chose the TT option as the front cuts are everywhere, at a super good price, and on paper they tear even the STI a new one...
For a highway car the TT's are a big thumbs-up from me, the primary turbo is so small, they spool to a factory std 16psi boost by 2000rpm. Once the Secondary turbo gets-up-to-party they absolutely fly, BUT...
it's the in-between that sux, the 'VOD' that Suparoo mentioned is an unfortunate reality. It is caused by a sudden exhaust pressure drop when the RH up-pipe 'opens' to spool the secondary turbo, then BOTH turbos have to spool again. This can be Greatly reduced by fitting a Zero/Sports sequencial (that's how they spell it)controller, which lets you tune this turbo staging by moving it in the rpm range (higher rpm-more gas quicker) but that, of course is a trade-off with having more flow through the restrictive primary than necessary, I thought 'I'll fix that-I'll fit an external wastegate' - not worth it!!. The later model variants are a lot better, my cousin has a MY04 B4 and it is almost non-existent ON ACCELERATION. Now comes another BUT...Where the VOD becomes a problem is as funny as it sounds, on decceleration, for example if you change gears and end-up in the VOD, like going from 4th-to-3rd round a corner at a set of lights, your screwed, you aint gonna spool that baby again unless you go to 2nd!
Believe me, I did almost every mod imaginable to mine, and you can't get rid of it, you can just mask it, learn to drive with it and tell your mates "yeah it does that, because..[stuff they don't understand nor car about]..oh, never mind, have you heard that new Art Vs Science song? Wait I just got positive pressure again-there we go!" Not to mention, forget fitting a BOV, the pressure from the tiny turbo is ALWAYS greater than the manifold vacuum and holds them open, I thought 'I'll fix that too, I'll fit a HKS SSQV'-errr, wrong!

Don't get me wrong, they run beautifully, and they go like stink, but they are way more complicated than they need to be, and if you want to tune them all the TT specific parts are hand made, or very selective from japan.

If I was doing a transplant again I would go for a single turbo, I just bought a MY99 WRX for my wife, and it goes beautiful in standard trim, a lot more drivable than the TT, sure it spools a little later, but it stays spooled as long as SHE wants it to! I guess the TF035 equipped forester would spool earlier more like the VF18/VF25 on the TT, either way IMHO, single turbs is a better option.

However...if I had to repace an EJ20 I would grab a GTB engine and strip all the TT gear off it and put the whatever single turbo stuff on because the GTB engines are very good value, they have the STI cams, they have the big injectors, the big throttle body, the late model ones have forged pistons and they are available everywhere!

sorry about the rant, but you kind of asked for it hope it helps!

Yeah thanx!
It definately helps, alot!
I'm still convinced i want to think of a tt settup at least
eventually and maybe try different combinations of turbos?

Is it a seperate exh manifold for each turbo or one with
a equalizer pipe between both up pipes?

Rumour has it that some of the guys (ASG) over here have been experimenting with open ecu tuning have had quite pleasing results in "tunning" the stock ecu and working around the VOD on the B4 model....rumour mill and i would ring them to really find out the gos...

It is one manifold, that feeds the LH primary turbo all the time and has an exhaust control valve on the RH up pipe that opens at 4000 rpm that lets half the gas up to the secondary. There is a mod that you can do so they run parallel turbos, I cannot comment, as I never tried that. It is just a matter of changing some vacuum lines. Another potential improvement may be had from a large front founted intercooler, as the larger volume of compressed air in the cooler and pipes would take longer to discharge when the boost drops during the turbo staging, this would of course would be a trade-off to more initial lag, I never went down that road either.

hmm, maybe a H pipe sort of system for the turbos, feeding them both
full flow all the time and
have the outlet of the smaller turbo compressor feeding the inlet to the compressor
of the larger turbo?
both turbos running of one controller?

twin charge style!

thoughts?

i didnt know it was that complex nev!

...not a bad idea, unfortunately the 'larger' turbo isnt large enough to do that, and in fact it doesn't have a wastegate either, exhaust flow to it is regulated by a duty solenoid on the exhaust control valve, which also keeps flow going to the primary from the RH side when open aswell.

I found a really good pdf on it all once called 'twin turbo operation' I will see if I can find it, it would interest you.

Here are a few more diagrams to help explain it






A full article with a good explanation can be found here Autospeed.com - Subaru Liberty B4 Tech Overload

AHHH WOW, COMPLEX!

ive got a much simpler idea!

so much pipework!!

H-top wrote:ive got a much simpler idea

Yeah a single turbo

Trying to simplify and improve the TT setup at the same time will only end in tears. Its complicated for a reason.

i cant think of a reason it cant work?

it would just take good planning, loads of
other engines use it, and simply.

just because couldnt get it right nearly a decade ago,
doesnt mean it cant be done.

life isnt easy
more pondering required

supercharger turbo / boost all the time use to drive the big one with no lag at all and lots of air that cold

been thinking of that too, but way to costly for me