WRX 08-14 and Legacy GT Owners, The Wait Is Over

Introducing the Steam STX 71 with stock Lecgacy GT and WRX 08-14.  There aren’t as many options out there for the LGT guys, and none come to mind that make make STX 71 power.  Our customers have been asking us for a while, when will you make a STX 71 for in stock LGT fitment?

Well, here it is!

Steam STX 71 LGT

This turbo has the same 11-blade GTX3071R spec billet compressor wheel and TD06SL2 9-blade turbine as our STI model, but now with housings and lines for stock LGT fitment.

We are looking forward to the first LGT or WRX 08-14 guys to make 400-450 whp with a stock style turbo.

 

Turbo Billet Compressor Wheels: SteamSpeed vs. Blouch vs. ForcedPerformance vs. Garrett

For turbochargers, compressor wheels are super important.  They ultimately dictate how much power your car can make.  Selecting the right turbocharger wheels can have a huge impact on how the turbocharger influences your car’s performance.

“Billet” compressor wheels have been out for a few years now.  Brand names used for turbos with “billet” compressor wheels are names like: “STX” for Steam Turbochargers, “XT” for Blouch’s turbos, “HTA” for  ForcedPerformance, and “GTX” for Garrett turbos.

Most people assume they are all basically the same, but they are not.

Our billet compressor wheels improve performance over cast wheels of the same dimensions by increasing the blade area, and also decreasing the mass of the wheel simultaneously.  We know our competitors do some or all of these things with their “billet” designs.

Here are some of the techniques used to make “billet” compressor wheels out preform their cast counterparts.  These are well known to us and our competitors.

Billet Compressor Wheel

 

Given wheels that are the same size, aerodynamics are super important.  They determine the wheel’s flow, and efficiency which both relate to things like whether a turbo can make power at 30 psi.

Large companies like Garrett or Mistubishi make wheels with 3rd order geometries.  In simple terms, that means, the blades have more complex shapes.  SteamSpeed also uses 3rd order geometries in some of our newer turbochargers.  However, it takes quite a bit longer to mill a 3rd order surface into a compressor wheel and incidentally more money as well.

Many smaller turbo manufactures like Blouch Turbo or ForcedPerformance might or might not bother spending the extra time and money to mill their compressors this way because most  customers don’t know the difference and it saves money for manufacturers on their bill of materials.  Garrett takes the time to mill their full geometry even though it costs more.  SteamSpeed is also doing this now with our prototype production.

It is much cheaper to mill the blade shape in one pass, but you can only mill  less-complex compressor wheel shapes like this.  The primary reason to use this method is to save money for the manufacturer by reducing machine costs with faster cut wheels.  This is an example of what flank-milled with a lower order geometry compressor wheel looks like:

Flank Milled Compressor Wheel

You can clearly see the lines horizontally down the blade where mill cut the blade in one single pass.

Garrett GTX and some newer Steam STX turbos do use 3rd order blade design, and use a much more expensive milling process than flank milling.  Look at the detail of this Garrett GTX wheel.

Garrett GTX40 Notice there are vertical lines in the blades instead of horizontal lines on the blades.  This point-milling process is a lot more time consuming, and therefore, more costly.

Do you have a ForcedPerformance HTA turbo or a Blouch XT turbo?   I have personally owned some of their products myself.  Are you thinking about buying one?  Before we created SteamSpeed, I was considering buying a Blouch XT turbo.  Ultimately I bought a Garrett GTX based turbo instead, and now only install Steam STX turbos.  Make a careful inspection of the wheels on the turbo you already own, or are thinking about buying and draw your own conclusions.

Here is a Forced Performance HTA 68 compressor wheel.  How does it look milled?

ForcedPerformance HTA68
ForcedPerformance HTA68

Here is a close up on the Blouch Dominator 3.0 XT-R turbo.  How does the wheel look milled to you?

Blouch Dominator 3.0 XT-R
A close up of the Blouch Dominator 3.0 XT-R

Lots of people are using turbos with lower order aerodynamic designed compressor wheels.  They can still make good power, but they are not as effective at making power as higher order blade designs.

SteamSpeed’s competitive advantage has been our keen understanding of how to pair turbine and compressor wheels together, resulting in ideal performance.  For our turbochargers that have been issued flank-milled compressor wheels, we have mated them with ideal turbine wheels so that they make great power, produce high boost, while also enabling us to keep costs down for the customer.  Aside from eliminating the middle man and selling direct, this is another reason our turbochargers cost less than our competitors’ while outperforming their comparative products.  SteamSpeed maintains competitive pricing with turbochargers equipped with point-milled compressor wheels, but the pricing on those is understandably a bit higher than turbochargers with flank-milled wheels.

Look at the detail of a Steam STX 71 for LGT.  Notice how the blades have lines running from top to bottom, rather than horizontal marks indicative of a flank mill process.

Steam STX 71 for LGT compressor wheel

At SteamSpeed, our goal is to make the superior product, whether we use flank-milled or point-milled wheels.  For our most premium turbochargers, this starts with not cutting corners with lower cost wheels, and only putting the best wheels in our turbos.  It is understandable that if we are trying to be competitive at a lower price point that we may not be able to use point-milled wheels, but our flank-milled wheels will still be of superior cut and technology, therefore outperforming our competition at similar price points, or even higher in many cases.   Eventually, our goal is to be able to us point-milled wheels on all of our turbochargers, not just the higher cost ones.

Turbo Wheel Tech: Basics

Hello Interwebs,

This is Sam from SteamSpeed, and we are briefly going to talk about modern turbo wheels.

For a quick refresher, here are the super basics concept of how a turbocharger works:

  • Hot exhaust gasses coming out of an engine flow  through the turbine housing scroll (painted red in the picture)
  • The scroll focuses the gasses to a point and aims it onto the turbine wheel blades
  • This causes the turbine to spin on its shaft
  • The other end of the shaft is connected to a compressor wheel
  • The faster the turbine spins, the faster the compressor wheel spins.  To give you an idea of wheel speeds, the turbine and compressor wheels can spin up to 250,000 RPM.
  • As the compressor wheel spins, it compresses the air coming into the engine from the intake path
  • In super basic terms, the speed of the spinning compressor wheel will make boost and flow a certain quantity of air
  • As we compress air, it will become hot.  Ex. an 18G at will take 75 F ambient air compress it to 19 PSI, and the exit temperature will be about 300 F.  Normally intercoolers are used to bring down the charge temperature closer to the ambient temperature.
  • The boosted intercooled air is forced into the engine

Turbocharger Cutout

If there interest, we can do deeper dives in the details if anyone is interested.

Compressor Maps Explained

Waning: Physics Content 

Now with the quick primer out of the way, you can see that the aerodynamics of the wheels are super important.   It determines how much force is applied to the wheels.  Torque (moment of force) is applied to the turbocharger’s shaft.  Torque is:

\boldsymbol \tau = \mathbf{r}\times \mathbf{F}\,\!

Next, you might think that you can also increase the radius “r” of the wheels to increase the torque.  This is true, but it also increases the mass moment of inertia which in layman’s terms means the wheels resistance to start or stop spinning, so the bigger the wheel (“r”) and mass (“m”, the harder it is get the turbo spun up.  Inertia is:

 I = m r^2

End: Physics Content

How do you make higher performing turbos?

These are the basic laws of physics which cannot be cheated.  How do turbo manufactures then make high performance turbo chargers?

  • One way is to increase the wheels’ size.  The side effects are increased flow, but also more lag by increasing both “m” and “r”.
  • Anther way is keeping the wheel sizes the same, but increasing the efficiencies of the wheels.  More on this later.
  • Another option is to decrease mass (“m”).  This will reduce the inertia
  • You can also decrease parasitic friction on the shaft by using ball bearings instead of journal bearing for example.

The fact of the matter, is that you try to do all of these things in balance.  We will follow up with some more posts on these points.