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Need Help with 2stage booster

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#1 SlaterKey84

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Posted 17 August 2014 - 06:25 PM

my brother bought a 98 twin turbo 5speed liberty/legacy and we have been told that the only way the boost can be raised is by flash tuning the computer.... is this correct? the car is 100% factory standard.

also there is a bit of a dead spot between 4200rpm and 4500rpm apparently that is where the primary turbo shuts off and the secondary one kicks in... is there a way to fix this so there isn't much of a dead spot (if any)

 

what we WANT to be able to do is....

RAISE THE BOOST (but apparently can't due to boost cut off)
add a B.O.V

install a dual stage boost controller

install a boost guage



#2 AB501UT!0N

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Posted 17 August 2014 - 08:00 PM

Hi mate I would replace all the vac lines and install a boost guage so you can get a base line figure of how much psi your making to make sure there is no issues causing a loss of boost pressure and regarding the Valley Of Death I would get my hands on a Zerosports Sequential Controller so you can make the turn is have less VOD and the reason I would suggest this is because it is the cheapest that I know of with it raising boost pressure. Also you can buy Hdi boost controllers for you car that are made for twin turbo setups but I have no idea if they are any good. Hope this helps

Chris

#3 SlaterKey84

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Posted 17 August 2014 - 09:11 PM

yeah it helps... what does the zerosports sequential controller do? how do you install it?



#4 SlaterKey84

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Posted 17 August 2014 - 09:32 PM

also does can anyone tell me IF the 98 TT legacy's have a factory boost controller? IF SO ... where is it?



#5 AB501UT!0N

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Posted 17 August 2014 - 10:27 PM

yeah it helps... what does the zerosports sequential controller do? how do you install it?

 

It controls when the first and second turbo spools up so you can remove the VOD



#6 Tim.

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Posted 19 August 2014 - 12:06 AM

The ecu is the factory boost controller. There are various ways to increase boost like by modifying the duty cycle of the boost control solenoid or altering the size of the hole in the restrictor pill which lives in the wastegate line.

But first, how much boost is he running at the moment?

#7 Jimbo

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Posted 19 August 2014 - 06:37 PM

If i was your brother, i wouldn't mess with it unless he sits down and reads the entire "Your Guide To Twin Turbo" thread. All of your questions are answered in that thread. If you start playing around with it, without knowing what your doing, it will end in tears. Guaranteed. 

We need to know exactly what it is. Is it a Legacy (GT, GTB, RS, RSB) or a 1998 Liberty shell with a conversion? It helps to do some research and give us more information so we can help you.


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#8 allpaw4

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Posted 20 October 2014 - 03:47 AM

Boost gauge is reasonably easy to install - tap into one of the vac lines on the manifold and T off a line to the gauge. Just dont mistake one of the larger coolant lines as a vac line.

 

Dual stage Boost controller is pointless - They work by fooling the ECU into thinking things are normal when the controller is making changes. The subaru system is different, and you'll end up with check engine lights etc.

Raising the boost is also pointless - the turbos on these are very small - and as such are running very close to their efficency limits - increasing the temperature of the inlet charge is a great way to introduce knock to a system that has a hard enough time dealing with it anyways.

 

I take it by the 'add a bov' you want to change the standard one for a vent to atmosphere one? This is easy to do, but you'll have to do some research on what aftermarket models will fit on the standard position.

As per Jimbos comment - read the TT thread before touching these cars mechanically. They are finicky and dont like being fiddled with. Plus, the later model TT models were renowned for doing big end bearings stock, let alone fiddled with.

 

Now, without knowing the specifics of your car, all I can say re overboosting it is that the stock Gen 3's boost settings are within about 5psi of boost cut (well, effectively fuel cut in the early models). so any gains you put through are going to make negligable difference to your 'seat of the pants' power gauge. Plus, all it takes is a freezing cold night and its extremely likely you'll hit it by even upping it by a few pound.

 

Have a read of the above mentioned thread and see what you want to do then. Sorry for the bad news, but certianly do some research before fiddling fellas.

Its not a simple thing to just throw a boost controller on it and up the boost. Talking major upgrades before you can get decent power increases.

 

The dead spot you're talking about is commonly referred to as the 'Valley of death', and you are half right - its where the valves in the system start opening on the secondary side to get it spooling up. As a result there is a substantial drop in power as the primary can't keep up with the exhaust outlay of trying to spool the secondary. When the VOD is over, both turbos are working fully. It can be modified, but you are better off reading the TT thread before you change anything.

 

Cheers,

Ben


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