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  1. Following from our last blog, billet wheels are a current trend for upgrades with some stating they are a con and may look pretty, whilst others think they are essential in any turbo upgrade.

    Billet compressor wheels are made via machining the wheel from a block of solid alloy (billet). A billet is loaded typically to a 5 axis automated milling machine and machined from a computer-designed drawing (CAD). But are they all the same? They look it...

    Simply copying the original cast compressor wheel will indeed give you some benefit; the structural strength of the wheel will increase with the wheel being machined from solid billet rather than cast, but it wont improve performance...

    Going to the effort to produce a wheel in billet rather cast may seem a waste if you're simply copying the original. The fact that the billet option is stronger, means you can make the wheel thinner on the blades and on the base, as well as on the nose and the hub. Instantly, you reduce the weight considerably and also improve the air flow because, with a smaller nose and hub, the blade surface area increases. More power = Faster spool!

    Further developement work can involve producing wheels in different designs with differing blade height, blade counts, extended tips, and maximise the potential flow of a wheel that is the same size as the original. With the use of computer aided flow dynamics software there are many gains to be made... This is where billet upgrades are a must!

    At Turbo Rebuild we are looking for maximizing the potential gains to give the most power possible without affecting the driveability. A well specced turbo will usually transcend something that has a massive top figure. Below we look at an example of what potential a performance designed billet wheel can give.

    Side by side here we have a genuine Garrett T3 55 trim compressor wheel 409096-0014 compressor and our billet upgrade wheel.

    Billet Compressor wheel comparison

    First thing first, lets check the weight of each...

    Genuine 409096-0014

    Billet 409096-0014 Compressor Wheel

    Out of the box, the billet wheel is over 9 grams lighter, that is a 17% weight reduction. To get this reduction we have made the wheel thinner, by machining the nose and hub. We have also gained a larger surface area for the blade to pump more air.

    Compressor wheel nose

    Billet Compressor small nose

    The billet wheel has a 4.2mm smaller hub compared to the case original. This results in the size of each blade being 2.1mm wider, increasing air flow. If we look at a Garrett compressor wheel, it has a 4.2mm larger compressor than the 409096-0014 wheel. We find the 60 trim wheel (409096-0013) coming in at 0.2mm smaller at 46.5 mm.

    This wheel is starting to look good indeed... Lighter than the original, stronger than the original, larger flow than the original, in fact more flow that the larger 60 trim wheel!

    Now, with the use of flow dynamics, we can adjust the CAD diagram to assess where more potential gains can be found. In this particular wheel, extending the exducer tips as well as raising the height of the wheel sees more gains.

    Standard T3 Cast Compressor Wheel

    Extended Tip Compressor Wheel

     

    Billet wheels can look the same, some won't make any difference whatsoever. Choosing a turbo builder who knows how to maximise the performance, has knowledge and experience in modifying turbochargers, as well as the correct equipment to complete the work, is the way to get the gains you are looking for!

    In a following blog post, we will get the wheels built into cartridges and take some airflow readings to see how they do side-by-side and then onto a car for real world results!

  2. The word Hybrid in the Turbocharger world is rather a minefield.  A Hybrid by definition is simply something using different parts rather than the original to improve the design.  In Turbochargers this can be simply stronger bearings, larger wheels, lighter wheels, or even stock wheels that have been modified.  In the early days Turbocharger companies put Hybrid Turbochargers into stages.

    Stage 1 = Upgraded bearings and seals, Standard Compressor setup, Standard Turbine Setup

    Stage 2 = As above but also modified compressor eg Improved wheel, different housing a/r etc or multiple changes to the Compressor design

    Stage 3 = As above but also modified Turbine eg Cutback or larger turbine wheel, larger A/R etc or multiple changes to the Turbine design

     

    categorising made upgrades much easier to understand and explain.  categorising stages of upgrade then following into engine tuning confusing the matter as a Stage 3 Turbo is not required for a Stage 3 map etc.  This coupled with Billet compressors, different blade configurations and designs has made things harder still.

    Turbo technology and engine tuning has moved on leaps and bounds in recent times with all tuners and mappers wanting to be "The Best" and their cars to be "The Fastest"  Cars are mapped to within an inch of their life and Turbos too feel the brunt of this.  Power claims can at time seem rather optimistic to say the least.  This further makes building upgrade Turbos harder.

     

    Just because "Dave" made 300BHP on his standard Turbo doesnt mean the Turbo is rated to 300BHP, chances are the cars boosting far outside of its advised operating conditions and Dave is fitting a new Turbo every few months (if he's lucky)

     

    Its vital to fit a Turbo with a RATING to the power you want to achieve, not the Maximum physical power it can flow.  Hybrid ratings can seem low and as such may not seem worth the money, but the fact is, the unit will provide the power rating without stressing the Turbo and will last years rather than weeks/months!