Yeah, you need twin scroll headers and up pipe, which also means you'll need a new sump and oil pickup. Vision R sell tomei twin scroll headers, and psr over east sell gt spec ones. I had GT Spec ones on my conversion, just make sure you get the gaskets, as they are hard to find. For the price JWS charge for subaru ones, your better off going down the aftermarket route, unless you want to buy that VF36 kit which is on sale on rexnet at the moment. Its quite a good price. The VF36/37 is capable of supplying a lot of boost, but you need to modify the wastegate (i.e. make it stronger) to keep boost up top. Trust me, you won't regret it.

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John Stamos fan club lifetime member

awesome, wont be able to fork out for that kit straight up but will deffinately be putting money in the jar for later on.

thanks for ya's help.

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Foxey, sounded like you had a sweet package. Hey what did you do to your wastegate as I've a feeling the same mod will have to be done to mine. Spring perhaps ?

Guys I have a twin scroll VF37 that I should put up for sale, ceramic coated exhaust housing. I can source all the other parts needed too including gaskets for a kit.

J

I hadn't actually done anything to mine, but yes a stronger spring was going to be tried when the new motor was due to go in. I think an external gate would be really beneficial for running higher boost on the VF twin scroll turbos, as the internal gate doesn't really look ideal. The TD twin scroll exhaust housings look much better. It would be interesting to see how much earlier you can get a 36 to spool over a 37, as mine used to spool damn fast, and that was without AVCS.

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John Stamos fan club lifetime member

"apparently" a twin scroll turbo compared to same sized single entry turbo will fall behind in outright power.

correct me if I'm wrong? I'm talking max power and high stress applications...something to do with heat and friction....

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K.E.R.S!!!1

Well, theoretically the twin scroll should flow better at high rpm too, as the exhaust gas flows more smoothly through the turbine. I have never seen anything which would suggest otherwise, but I don't think there are many big hp twin scroll cars going around, except maybe for a few evos, and that 6 cylinder GC8 in the states. I made more power with less boost when I went twin scroll, although I did a few other breathing mods at the same time.

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John Stamos fan club lifetime member

The cold side is the limit of the power. Twin scroll and single scroll will both flow similar hp on the hot side if they are of a similar size. In drag racing though the single would probably be better for overall top top end at super high boost.

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From Forcedperformance.net

Q. What are twin scroll or divided inlet turbine housings? What are the benefits of using a twin scroll turbo?

A. A "twin scroll" or "divided inlet" means that there are two separate volutes within the turbine housing. The main reason for doing this is to isolate the pulses coming from each exhaust port and maintain more of the pulse energy from each cylinder all the way down to the turbine wheel. There are no differences between the turbine wheels used in open or single inlet turbines compared to those used in twin or divided inlet turbines.
Generally speaking, a divided inlet turbine setup will respond faster and produce boost quicker than single or open design of the same nozzle area, of course this is dependent upon proper execution. The simple fact that a divided housing is used does not guarantee these results.

While it does not cause any problems or harm to run a divided inlet turbine housing on a manifold that is an "open" design, none of the benefits of the twin inlet will be seen.

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Top end power is more to do with the Mass or Energy of the exhaust gas flows into and out of the turbine and exhaust housing of the turbo. The greater the gasses that can be flowed up to a point, the greater the HP output for the same sized turbo. Well until you end up outside the compressors efficiency range. One would think that with virtually nill pulse energy interferance that the turbine wheel would work more efficiently generating more HP at any given RPM.

On the flip side maybe twin scroll headers may have a slightly reduced internal overall diameter piping into the turbo to speed up the exhaust gas flows and promote quicker turbo spool up at the expense of the mass of gasses that can be flowed at high RPM's.

Anyone got some piping internal OD measurements ?

A VF34 / VF36 comparison would be interesting. Same compressor housings, but again different exhaust housings. PZ18 compared to PZ25. I would be putting my money on the VF36 for outright HP as well due to virtually nill exhaust pulse interferance.

J

You'll love this all ya Nerds:

Revenge of the Nerds

Lessons in Turbine Housings

By Mike Kojima

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There are basically two types of turbine housing configurations, tangential and on center. Tangential housings have the turbine inlet coming into the housing at a tangent to the turbine wheels. On center housings have the turbine inlet coming directly into the center of the turbine wheels axis. A tangential turbine housing is greatly more efficient as the gas path feeding the turbine has a straighter shot into the housing and a better impingement angle on the wheel. The gas entering an on center housing must go around a kink in the housing, which causes turbine efficiency to suffer by up to 10%. There are studies that show that a 2% gain in turbine efficiency can offset gains of up to 25% of the turbines inertia so a 10% loss in efficiency is quite significant. However the on center mounting can often give a bit of mounting flexibility to solve a difficult fit problem but because of the efficiency losses it is better to try to find almost any other solution to a packaging problem.


Another interesting aspect of turbine housing design is divided and undivided housings. A divided housing is exactly how it sounds, the scroll of the turbine housing is split in two. A savvy tuner can use a divided housing to his advantage on an engine with few numbers of cylinders. A divided housing works best on a 4-cylinder engine with some advantages on a 6 cylinder with a properly designed manifold. When a divided housing is used, usually cylinders 1 and 4 are fed into one side of the scroll and cylinders 2 and 3 are fed into the other side. The cylinders fed into each side of the scroll are as far apart in the firing order as possible. This allows the turbine to be hit with 4 distinct pulses as the engine goes through its firing order. This improves turbine efficiency, sometimes to the point where up to one size larger A/R housing with it’s attendant lower backpressure can be used, either that or less turbo lag can be enjoyed with the same size A/R housing. The divided housing can also improve volumetric efficiency by making reversion from adjacent in firing order cylinders much more difficult. This is because there is a great deal of separation in degrees of crankshaft rotation between the valve opening events of the adjacent cylinders. In order for a reversion pulse to contaminate an adjacent firing cylinder, it has to travel back through the spinning turbine blades and up the other side of the divided turbine-housing scroll to get to the adjacent cylinder. This is pretty difficult and the pulse will tend to take the path of least resistance, past the turbine to the area of lower pressure.

Rest of the article....

http://www.nissanperformancemag.com/march06/nerds/