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I've been talking to a lot of people with upgraded oem style turbos VF40, VF46, VF52, and so on. I wanted to post my thoughts on what is an effective upgrade and what is not from a turbo geometry perspective.

 

For example, I dont advise installing a larger compressor wheel on a VF40 as that configuration is already largerly turbine restricted. Installing a bigger comp wheel further unbalances the flow rates, increases back pressure at full boost, and may hurt power levels overall.

 

(***under construction***)

 

http://i463.photobucket.com/albums/qq357/tuningalliance/comparo.png

 

I'd like to talk about wheel sizing between compressor and turbines. As you can see I highlighted the "Inlet/out" ratio, which is simply the inlet diameter (compressor inducer) divided by the outlet diameter (turbine exducer). A perfect turbo would have a 1.00 ratio, and as you can see a GTX3582R is pretty darn close. A value over 1.00 indicates the turbine section is the restriction point, where as a value under 1.00 indicates a compressor restriction point.

 

A stock VF40 has a 1.08 ratio. Meaning is largely turbine restrictive, and upgrading the compressor will only worsen this ratio, and will not allow for additional power as the small outlet is the overall restriction point. This turbo would likely benefit from turbine wheel clipping or turbine housing porting. As upgrading the turbine section doesn't really make financial sense.

A stock VF52 has a 0.96 ratio, meaning it could benefit from a little bit bigger compressor inlet size. So a little larger billet wheel could be a helpful upgrade.

Edited by Tuning Alliance

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Next I want discuss the reality of putting a larger compressor or turbine wheel inside a stock housing.

 

When you machine the stock turbine housing to accept a larger wheel, there are some disadvantages to be noted. A stock turbine housing has internal passages which are carefully sized in volume, width, and the delivery channel which directs flow on to the blades is a matching dimension. This gives the most effective delivery of exhaust into the wheel. If you install a larger wheel there is now a mismatch of these dimensions and a portion of the trailing edge of the blades that is not in fact hit directly with exhaust as it would in a turbine housing design for that turbine.

 

Many people only think about the increase in diameter when they are picturing the larger wheel inside the housing. I'm not saying it doesn't work, as it does work. What I'm saying that all of the bolt-on upgraded turbos, do not have the proper volume or channel to drive the turbine at its maximum efficiency. The same thing goes for the compressor housing. Other aftermarket non bolt-on turbos spool faster and are more efficient due to this fact. This is why I often urge people to use either a OEM turbo or a full rotated setup with a fully matched configuration.

 

http://i463.photobucket.com/albums/qq357/tuningalliance/turbine_1.jpg

http://i463.photobucket.com/albums/qq357/tuningalliance/detail%20turbine_1.jpg

Edited by Tuning Alliance

Contact us for all your tuning and performance parts needs! Etuning the legacy community since 2008!

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lol right from our discussion

 

People keep asking and I find myself explaining this stuff twice a day. Time to get it out there then I can just link people to it.

More to come!!!

Contact us for all your tuning and performance parts needs! Etuning the legacy community since 2008!

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  • 3 months later...
  • 4 years later...
  • 4 weeks later...
Does the 2005 Legacy GT turbocharger have a 12 blade billet from the factory? I ordered a 12 blade billet thinking installing it would make a difference or make an improvement.

 

 

9 blade on the hot side. Here's my old vf40

 

https://legacygt.com/forums/showthread.php/142-000-miles-oem-turbo-168561.html

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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