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Garrett GTX Turbo Tech

An Inside Look at the New Garrett GTX Turbochargers
By Mike Kojima

One of the current rages in the turbocharger aftermarket is the billet compressor wheel.  The traditional compressor wheel for most turbochargers is made of cast aluminum.  Cast aluminum is a reasonably good material to make a complex part such as a compressor wheel out of economically in large scale production.  However, cast aluminum is not as strong and does not have as good mechanical properties as billet aluminum.

One of the problems cast wheels can have are small voids and other internal defects.  These voids can cause points of stress concentration inside the compressor wheel which carries a lot of load due to the high rpm it turns at (up to and over 150,000 rpm in some cases).  These areas of high stress are called stress risers and can result in wheel failure. The other issue is that the mechanical properties of cast aluminum are limited as far as strength.  For these reasons a cast wheel has to be designed with these issues in mind and the blades are made thicker and the center hub chunkier and stronger.

Some high performance cast wheels are post processed with Hot Isostatic Pressing or HIP which is a process that subjects the wheel to extremely high pressures and temperatures (around 10,000 psi and 900 degrees) in an inert atmosphere, usually argon. This process reduces internal voids and improves the grain of the material increasing strength.

Garrett GTX Turbo Tech
The Garret GTX wheel is a 5 axis machined work of art, the 5 axis CNC machining gives the degree of freedom needed to design a wheel with no compromises in aero or stress.

Billet wheels have even better strength than HIP treated cast wheels.  A billet is a piece of raw aluminum stock that has been either roll formed or forged into shape.  This highly compressive mechanical working of the material greatly reduces internal voids and improves the metal's grain making it finer and more homogeneous.  This greatly increases the strength of the raw material.  Typical billet compressor wheels are CNC machined from rolled bar stock.

Garrett GTX Turbo Tech
The Garrett GTX series turbos use the same excellent dual bearing, oil damped, cartridge center section as the older R models. Garrett's world class OEM level engineering combined with new uncompromising compressors with designs not constrained by the mass production volume and price requirements gives GTX turbos a huge leap in performance.

 

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Comments
Steve
Stevelink
Tuesday, December 21, 2010 11:33 PM
Wow. Awesome article Mike!
Dusty Duster
Dusty Dusterlink
Wednesday, December 22, 2010 5:56 AM
Good reading, but I still don't understand how to read a turbocharger efficiency map. Can someone point me in the direction of an article explaining how to do so?
spdracerut
spdracerutlink
Wednesday, December 22, 2010 7:16 AM
Dusty, it's pretty easy. Looking at the GTX3071R map, at 40 lbs/min of flow rate at a pressure ratio of 2.5, the compressor is in the 77% efficiency island. At the same 2.5 PR, but 50 lbs/min of flow, the efficiency drops to ~71%.
Todd03412
Todd03412link
Wednesday, December 22, 2010 7:46 AM
This helped me out a lot, Dusty. The cummins site is great also, very barney style explinations of how to read maps for us not so smart folk.

http://www.z31performance.com/writeups/turboselection.html
Max Machine
Max Machinelink
Wednesday, December 22, 2010 7:47 AM
Great Article. Finally registered to the site.
It would be awesome to talk to the guy who performed the FEA on acoustic stress and fatigue.
BenFenner
BenFennerlink
Wednesday, December 22, 2010 8:34 AM
Am I having a brain fart, or do the billet GTX wheels have LESS surge margin (or resistance to surge) than their previous cast GT wheel counterparts?

That's what the maps are telling me...
spdracerut
spdracerutlink
Wednesday, December 22, 2010 8:56 AM
Benfenner, you are correct. The surge line moved to the right a little mostly due to larger trim on these midframe sizes. Smaller trim moves to the left. Gtx wheel still has a lot more map width.
spdracerut
spdracerutlink
Wednesday, December 22, 2010 8:59 AM
Dusty, you can go to turbobygarrett.com and go to turbo tech section.
Der Bruce
Der Brucelink
Wednesday, December 22, 2010 11:44 AM
Dang Mike, make me go out and find my old physics books and then borrow my friends mech. eng. books! And then borrow a book from the library on metalergy! Very technical write-up in deed. I'd love to see a little debate write up between you and Eric on where the pros and cons might exist between the GTX and BW series of turbos! Like which turbos match OEM VE curves better and therefore make direct turbo replacement/upgrades that much easier? I love how smart you guys are, but sometimes I feel like I need a pop-quiz afterward to see if I really "got it!"

"Back to school. Back to school. To prove to dad that I'm not a fool!"
Fly'n_Z
Fly'n_Zlink
Wednesday, December 22, 2010 12:20 PM
@ spdracerut: That's good news on the smaller frame GTX wheels having a surge margin moved to the left (you can see it when comparing the GTX3071R vs. the GTX4294R). Can't wait to see the map for a GTX2860R or equivalent. Any idea how far away we are on a release for these smaller frame size turbos?
Mike Kojima
Mike Kojimalink
Wednesday, December 22, 2010 2:05 PM
If you see the notch to the right at higher pressure ratios, that's due to the ported shroud.
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