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Old 06-07-2010, 01:13 AM   #1
Cervantes
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Default how to get more bang out of a twin turbo?

when i punch it, my first turbo hits hard, then my 2nd turbo kicks in and i feel a lag. once i hit at about 4000rpms the boost drops and my car doesnt accelerate as fast. i have a boost controller, intake and BOV, but they only seem to really effect the first turbo. i know in my friend's skyline, he has an intake and BOV going to each turbo. is this something thats possible with a twin turbo legacy? or is there a way to adjust or change settings so that they equally accelerate?
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Old 06-07-2010, 04:57 AM   #2
ReubenH
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How to get more kick out of a twin turbo? Convert it to single turbo, plop an ECU in, and bam, you'll be grinning from ear to ear.

Seriously, the only TT that's worthy is the face lift BE/BH TT setup. They have and ECU which you can tune as well, and get a few pony's out of. I've been in a BH that's had this done, and it's something special!!!

BUT, a yr 2000 legacy still has the the old V5/6 style 4-plug ECU, and phase-II engine. The plus side of this you can drop V5/6 STi gear into there, and immensely improve things

Here's the thing. Sequential Twin Turbo was the cool thing back in the late 90's (and VERY different to parallel twin turbo, which is what your mates GTR will have). It meant you could have a VERY quick spool, but still bucket loads of power up the top end (as much as the STI!) Unfortunately, the implantation of it means driving with it is a sack of ****, if you like technical driving at all. They are only good on the motorways. The other downer to the older TT's is that they are impossible to mod and get power out of. There are a few things you can do, but you're very limited.

You need to weigh up the options here.

Converting to single will require you do the work on the car yourself, you need to buy the parts you need, and you need to know what those parts are, and how they are different from other generations (i can help you with that though). The upshot is you'll basically be running a high compression STi motor in your car, it will go like a stabbed rat, and will be easily upgraded, and won't bog with vod! The single conversion is what you want if you have future plans for the car, if you want to keep up with skylines, or if you like the twisty roads out in the mountains.

OR, you can do a few things to the current setup. There's the Zerosports sequential controller, which will allow you to play with the crossover point (point where it goes from single to twin), you MIGHT be able to get the ECU tuned. Go to some performance shops around town and ask if it can be done. Can get an exhaust done, i recommend doing the whole thing, not just the muffler and mid-pipe. Also, the BOV, i'd go back to factory, messing with that thing on a twin turbo will cause bigger problems. Also, go back to a factory airbox and filter too (i'm not advising this, i'm telling you!), pod filters **** up twin turbos BAD if you get them wrong. If it's too small, it will rob power on secondary, to the point where it will fell like it's not boosting in some bad cases.

Woops. done it again.

Best of luck mate!
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Old 06-07-2010, 07:21 AM   #3
Cervantes
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thanks for the tip. the intake makes the car feel like its breathing better, but you may be right about it once the 2nd turbo kicks in. im getting a whole exhaust, only problem is finding one that fits. i'm going to naha and getting one made in the next couple of months.
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Old 06-11-2010, 11:18 AM   #4
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You don't have 2 turbos. Research...
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Old 06-11-2010, 12:11 PM   #5
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He's in Japan with a B4 Blitzen so yeah he does...
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Old 06-11-2010, 02:32 PM   #6
Cervantes
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yup....ive read a lot in the last few days. i now know about the spot where the 2nd turbo kicks in and you have "breather" period. ive adjusted my boost control and got it to where it gets rid of as much of the drag as possible. im not going to mod my car to just one turbo, so i guess it is what is is.
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Old 06-12-2010, 03:27 AM   #7
ReubenH
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Quote:
Originally Posted by DankWRX View Post
You don't have 2 turbos. Research...
Herpa derp derp.

Quote:
Originally Posted by Cervantes View Post
yup....ive read a lot in the last few days. i now know about the spot where the 2nd turbo kicks in and you have "breather" period. ive adjusted my boost control and got it to where it gets rid of as much of the drag as possible. im not going to mod my car to just one turbo, so i guess it is what is is.
The said breathing gap between turbo's is affectionately called the VALLEY OF DEATH. VOD for short Getting stuck in VOD also refers to when you change gear right while it's switching to twin, and thus get stuck with no boost for quite a few seconds.

I'll fill you in a little on how subaru's twin turbo works. It's a sequential system, that is, in the low revs, it acts as a single turbo, the second turbo is totally cut off and isolated. Since the turbo's are very small, spool is very quick, and you get boost from 2000-4000rpm just fine on the tiny primary. Just before secondary kicks in at around 4000-5000rpm, the exhaust valve opens half way to start spooling secondary. At the point where it switches to twin turbo, the exhaust valve opens fully, as does the intercooler valve, and the whole system starts working as a parallel twin turbo. Unfortunately, this whole transition isn't the most smoothest, and VOD is a side effect of that pre spooling of the secondary. The exhaust is being bled off the primary, to spool the secondary, even though secondary still isn't being used.

VOD is a side effect of sequential twin turbo, and is impossible to eliminate. HOWEVER, there are some gizmo's that can help. The Zerosports sequential controller is one. While it doesn't fix, or even make any attempts to fix vod, it does allow you, the user, to pick and choose at what RPM you want the crossover, or the switch from single to twin happen. I found with my GTB, that if i bumped it up a good 600rpm from factory, i less frequently got stuck in vod around town. And when it did eventually switch, the gas flow through the turbos was that much more, that the transition and vod was allot quicker, and actually happened with quite a satisfying kick. the downside is you stayed on primary longer, and could notice it very much start to run out of puff past 4000rpm!

Twin turbo in the BG/BD's (what i have) also is not nearly as good as in the BE/BH's (what you have) so the effect of the controller was much more noticable. I've installed about 7 or 8 of these controllers now, on virtually all iterations of subaru's twin turbo, and they work best by far on the older BG/BD's. The BE/BH's seem to not really benifit as much. And the Rev D BE/BH's don't even need them as the factory TT setup works very very well as is.



Did you ever find out if your ECU is tunable mate?


Oh, have a look in depth at this site. It has pages of info on twin turbo, including a description on how it works going into a little bit more depth than my attempt above

http://www.veloce.pwp.blueyonder.co.uk/

http://www.veloce.pwp.blueyonder.co....n/ttopprt2.htm

Last edited by ReubenH; 06-12-2010 at 03:54 AM.
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Old 06-12-2010, 09:12 PM   #8
Cervantes
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i've been looking into whether or not its tunable, but havent found much except the same answer im asking. im hoping it is because after i get everything i want done to it, i would definitely like to get it tuned.
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Old 06-13-2010, 06:39 PM   #9
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i just found out from a very knowledgeable person that it can be tuned.
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Old 06-13-2010, 08:44 PM   #10
ReubenH
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Good news. No start saving and do it :P

Get a full turbo back exhaust first actually.
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Old 06-13-2010, 11:14 PM   #11
Cervantes
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i just ordered my exhaust...had to get one made because i couldnt find one to fit my bumper. after i get my exhaust installed and buy a new tmic, ill get my car tuned. as long as nothing else pops in my head after getting those 2 things done.
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Old 06-14-2010, 02:04 AM   #12
Cervantes
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i have the apx-i avc type r boost controller, would i benefit from getting the Greddy Emanage Ultimate installed on my car?
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Old 06-14-2010, 05:13 PM   #13
Cervantes
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found out it won't work for my model car
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Old 06-20-2010, 12:39 AM   #14
ReubenH
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the AVC-R is a good choice for the car btw. They can work well pared with a sequential controller (if VOD is bothering you.) Did you get a turbo back exhaust? You'll DEF want to get the y-pipe.
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Old 06-20-2010, 05:38 PM   #15
Cervantes
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got a cat back exhaust
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Old 06-21-2010, 07:56 AM   #16
ReubenH
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You can do better than that! don't waste your time tuning it till you get a PROPER exhaust.

You should be able to just be able to buy the dowpipes/y-pipe separately and combine with the existing exhaust.
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Old 06-21-2010, 08:41 AM   #17
Cervantes
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i have to be careful what i do with my exhaust. in japan, we have a JCI, if i cant pass that, i cant drive.
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