Interesting article about Billet vs. Cast wheels

[Halon]

http://www.turbobygarrett.com/turbob..._Machined.html

Thought this was interesting and worth sharing and hearing what others have heard about this topic. Seems to be a lot of hype now a days about billet wheels, but is it all just hype?

[goodhart]

As far as I have heard, the reason why the billet wheels end to be more efficient is the newer more efficient design of the compressor wheels.

They say they are also easier to be made because cast tooling is expensive, but yet they charge more for the billet wheel. That part I don't understand.

[santa]

The reason why billet wheels are more efficient is because they are lighter then the cast wheels /thread

[Super Bleeder!!]

I didnt read the link (yes i am that lazy), but anyone thinking a machined wheel will make more power than a cast wheel of the same dimensions needs to think about the concept a little harder.

[Super Bleeder!!]

Originally Posted by goodhart

As far as I have heard, the reason why the billet wheels end to be more efficient is the newer more efficient design of the compressor wheels.

They say they are also easier to be made because cast tooling is expensive, but yet they charge more for the billet wheel. That part I don't understand.

Exactly right on your first comment.

On the subject of the second part: setting up a part to be cast is initially expensive but cheap in the long run if the production numbers are high.

However, thats not to say machining wheels is cheap AT ALL. CNC machines are ridiculously expensive and the cutting bits wear out (and they're not cheap.)

[Kracka]

Just another hot new trend... If it's lighter then great, otherwise if the dimensions are the same it's no different.

[Shane@DBPerformance]

It's the design of the wheel that makes the biggest difference. Even Garrett has new design billet compressor wheels now, the billet GTX GT42Rs flow way more air than the older ones, with essentially the same size wheel. Cast vs CNC machined or heavy vs light does not make a compressor wheel flow more air.

From that article "For either of these turbos, a cast aluminum wheel using the same dimensions and blade designs would have performed equivalently in most aftermarket applications. "


http://www.turbobygarrett.com/turbob...ochargers.html

"Forged, fully machined wheels (billet) for expedited release"

[scheides]

Yea I would think having billet in stock and ready to rock would make prototyping way more efficient too. Real-world turbos going out the door and should last a lifetime if they perform as expected. If not, rip them apart, melt them down and re-cut into more wheels

[CarPsyco84]

Originally Posted by Super Bleeder!!

Cutting bits wear out (and they're not cheap.)

Depends on the material being cut, Aluminum can be cut for practically forever with the same carbide endmill... Stainless or other high nickel alloys... not so much. The reason the wheels might be expensive is the fact that you need a 5 axis CNC mill to do turbo wheels. And the number of hands the part goes through by the time it gets to the end user. Machining aluminium with the right tooling is like cutting butter with a steak knife.

[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!

[Mwolf83]

Originally Posted by CarPsyco84

Depends on the material being cut, Aluminum can be cut for practically forever with the same carbide endmill... Stainless or other high nickel alloys... not so much. The reason the wheels might be expensive is the fact that you need a 5 axis CNC mill to do turbo wheels. And the number of hands the part goes through by the time it gets to the end user. Machining aluminium with the right tooling is like cutting butter with a steak knife.

This isn't always the case either, yes when cutting aluminum the tooling will last longer, but the tooling will not last "forever" and sometimes not long at all. I work in a machine shop where we make aluminum cases for Polaris, Arctic Cat, Yamaha, Honda, etc....and we will end up changing some tooling whether its endmills, drills, facemill/bore head inserts, or whatever the tool may be every couple hundred to couple thousand parts. There are even some parts that may require a tool change ever couple part.
There are hardened steel shafts that get bored out by carbide inserts that can even last as long as a few hundred parts before a change is needed. Many many many factors.

[Shane@DBPerformance]

Regardless of if it costs $5 or $50 to make a compressor wheel, the main cost of new technology is normally going to be R&D. You can't spend a million dollars developing a new product and then sell it for $20 because it only costs $5 to make, unless you are going to be selling millions of them.

[FFPerformance]

I think there are some misconceptions about the wheels out there.... yes there is a bit of 'bling' factor that people are willing to pay for, and perhaps 'Billet' is equal to Titanium as a buzz word to sell by. Who knows.

I would agree that differences in comparing a cast vs billet wheel OF THE SAME DESIGN, would show similar results on the dyno, but keep in mind that most small run, and test compressor wheels are made by CNC. Generally these are of a newer design and potentially better performance than standard cast ones that have been around for a while.

But, to stir the pot , what about the material differences? A cast alum wheel is weaker than a billet version even if it's the same alloy. Most good billet pieces will be forged and therefore stronger. What does that mean? From some research I have done over the years, a stronger wheel will have less blade deflection, you would be surprised at how much the fins bend at full load, and you will have a performance gain from the added stiffness. What people should be talking about is the same wheel made of Titanium and see what happens.... ;P

$.02

-Bob

[Halon]

Originally Posted by FFPerformance

I would agree that differences in comparing a cast vs billet wheel OF THE SAME DESIGN, would show similar results on the dyno, but keep in mind that most small run, and test compressor wheels are made by CNC. Generally these are of a newer design and potentially better performance than standard cast ones that have been around for a while.

Exactly. I'm not trying to confuse the two, and what you said is exactly it. The reason I bumped this back up with another article is because I've heard from a few people recently who have said specifically that they were under the impression that a billet wheel will spool faster and produce more power simply due to the fact it is a billet wheel, and that it makes it lighter.

What makes the new billet wheels better is not because they are billet, it's because they are NEW. New better design, not because it's bling bling.

Also, which mainstream turbos are you aware of that are machined from a forged piece of aluminum rather than just a cast piece of aluminum? I ask because I have no clue.

Just because my BW is a cast wheel, doesn't mean it's not going to hang with, or exceed the performance of a PTE Billet of similar size

*Edit - from what I gather, it appears the new BW EFR comp wheels are forged billet wheels

[Super Bleeder!!]

Originally Posted by FFPerformance

But, to stir the pot , what about the material differences? A cast alum wheel is weaker than a billet version even if it's the same alloy. Most good billet pieces will be forged and therefore stronger. What does that mean? From some research I have done over the years, a stronger wheel will have less blade deflection, you would be surprised at how much the fins bend at full load, and you will have a performance gain from the added stiffness. What people should be talking about is the same wheel made of Titanium and see what happens.... ;P

$.02
-Bob

I have no background in manufacturing so take this with a grain of salt; but from what i know, a forging is strong/desirable because of the compressive residual stress near the surface which is manifested during the forging process. Once you start cutting into that surface and removing that layer, it no longer has the benefits of a forging. It is now a metal thing carved out of a larger piece of metal.