[Halon]

Another good article from Borg Warner regarding CAST vs. BILLET compressor wheels, confirming again that the manufacturing process has no substantial effect on the performance of the wheel. Just wanted to bring this up again as I've heard a few people make statements to me implying a billet wheel is superior simply because of it being billet. So just a friendly bump to remind everyone that it's the design/geometry that makes a comp wheel better, not the process in which it was manufactured



BW AirWerks

In general... yes, we can make anything if you want to pay for it In the performance and/or racing world though, there is really no benefit to using a "billet" CW other than it's shinny. Basically, billet, or FMW (Forged Milled Wheel) compressors came about due to OE applications requiring them. When a turbo is constantly being cycled from high speed to low speed, the wheel becomes fatigued and can eventually lead to a hub burst (CW splits in half). Imagine the compressor acting like a big drag slick like you see on top fuel cars; during the burnout, you can see them get skinny and "grow" in height... On a much smaller scale, the CW sees this same process over and over again, and over time this weakens the wheel, eventually leading to a fracture and possibly a hub burst. Now ask your self how many times you've seen a race car's CW split in half... I have never, and I've seen a LOT of failures. Even the billet aluminum isn't enough in some newer applications and we've turned to titanium which in its FMW form, is nearly indestructible. I've heard all the propaganda surrounding the billet wheel myths: higher boost capability, higher flow, higher efficiency, etc... The higher boost capability is the only one which is true, but not because it's machined and not true for racing use. OE diesel applications using FMW compressors can run higher boost pressures more reliably simply because they are less susceptible to fatigue as they're cycled from higher speeds (required to make more pressure) to low speeds.
So, why would anyone offer a billet wheel to the racing/performance market? Couple/three reasons:
- Some people just want them because they look really nice... and are willing to pay the cost difference.
- Because it already exists in an OE production application and it's easily installed into performance turbos, sometimes they're even interchangeable with existing cast wheels.
- Applications where a cast wheel does not exist (maybe a larger inducer is needed) or production volumes are believed to never be high enough to justify tooling costs.
Are they cheaper than cast wheels? ...NO. Even in high production volumes, a billet wheel will always be more expensive than a cast wheel. However, if a company wants to make a compressor all their own (not using an existing "big" turbo manufacture's wheel ie. BW, Garrett, Holset) it would most likely be cheaper as they would have to tool up to make all the cast versions. If a company makes a mistake in the design of a billet wheel, they can simply keep changing the program until they get something that works... The OE manufacturer does all the development work up front to arrive at the best possible design for what's needed. Once the design is finalized, a "master wheel" is machined and used for the tooling master... that's right, all cast wheels get their start from a very nice billet wheel that when tooling is made, creates the same exact performance characteristics in a much cheaper and faster to produce cast version.
Phew... Sorry for the long-winded explanation, but hopefully this helps explain why billet wheels exist. Short version is billet wheels are no better than cast wheels for any performance or racing application I'm aware of... but they sure do look great!