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