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Parallel Twin turbo bg5 gtb


4x4fun

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I know this kind of thing has been covered before but looking to get thoughts on a specific idea.

As a cheap alternative to converting to single turbo has anyone thought about cutting off the secondary turbo flange and replacing it with a primary turbo and removing all the twin turbo gear and running an wrx sti ecu and aftermarket boost control. I realize there could be a decent bit of lag but the system should be able to flow a decent amount of air and perhaps have a similar fuel economy to a wrx because of staying off boost under mild driving. Would this be easy to get a custom tune?

Any opinions/ideas (apart from single turbo is better lol)?

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In my head sounded alot easier because of keeping existing piping and afaik the exhaust y pipe and intercooler should all be able to fit(might have to use the secondary turbo compressor housing. The idea is so it has semi equal length headers (2 cyl feeding each turbo) and could possibly reach 350bhp with exhaust and inlet mods and tune rather then sourcing another exhaust manifold and turbo and having to block off the oil and water lines plus might be able to disguise it as a stock legacy haha

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i thought of doing a similar thing to. But keeping both secondary and primary turbos and running them on a single turbo ecu and locking the turbos into parallel. but as said above easier to convert it to single turbo. Much easier and better results

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The reason i don't want to lock it into secondary turbo mode is that the flange/exhaust control valve for the secondary turbo is super restrictive and i figured i could use 3" downpipes with 2 primary turbos and not worry about overspooling. Does anyone have an idea how hard you could push 2 vf26's or similar. Looking at http://forums.nasioc.com/forums/showthread.php?t=1141476 it states they are good for at least 250whp(400cfm) is it all talk?

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No. Just no.

The quickest and best way to do what you are thinking is locking it in parallel and running an after market ecu.

You could take it further and get the syms or custom headers and remove the ecv but it isn't that restrictive in parallel.

Why would you want two primaries?

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The ECV could be drilled out/opened up quite a bit, or just replace the up-pipe completely?

It would work with a WRX ECU but it would be a pig until about 4500rpm. As said easier and better to just go single, unless your planning some sort of TT monster.

Rage siemeze that Marc had for sale not long ago:

photo107_zpsb933b2a3.jpg

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Wow those are some tidy headers. Thats a very good point and i wish i could afford a twin scroll system (would be much more ideal) but i was just thinking cost wise to get some decent power/flow and defeating the vod.

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Ugh, be/BH use one wastegate for boost control during parallel operation.

You can basically achieve what you are saying with a few vacuum mods and a boost controller.

Headers, ecv delete and tuneable ecu could take it a bit further. At this point a single swap isnt much of a stretch.

Or this, job done. http://www.subaruspeed.co.nz/products/parallel-turbo-conversion-exhaust-extractors-syms

Edited by GorGasmSpecB
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Most I've seen was 225kW @ wheels on a 2.2 block, a dude in aussie did it with twin Vf27's and a bit of crossed fingers

Your idea about twin primaries is backwards, they are the same turbine wheels on both turbos just a smaller exhaust housing on the secondary. I put a VF27 core into a VF26 exhaust housing for a laugh and it works quite well, quicker spool up but no power difference. You could use twin primary exhaust housings to try and help the spool up a bit maybe?

If you really, really wanted you could make a new up-pipe or just cut the ECV out of the existing one (there might be a wee bit of power there?) but the single wastegate is more than enough to control boost on the twins already (it bleeds off flow from the entire manifold, so yes it does control boost for both turbos - a lot of inline 6 aftermarket TT kits will use a single gate for two turbos)

There have been a few people do the "lock it in parallel and run a WRX ecu" thing, yes it does work BUT it's not achieving much - you can use the TT ECU just fine (just have to trick it a bit, feed the ECV signal into the differential sensor or something... I forget) - and the end result is not as capable as a properly sized single turbo is. Hell there was an old BD RS legacy in an NZPC mag in like... 1999 or so with twin secondaries and a possumlink, (once upon a time that was enough for a feature haha)

On a V6/V8 motor then sure, parallel twins are a good plan (see legnum/300zx etc) but there's no real need to bother with a subydoo, short of just doing something mildly different for internet lols.

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