gtm_maxwell

I Always wonder is what is the different in terms of Spool and performance for this Billet vs Cast Compressor wheel for 60-1.

Let's say we use both compress wheel on a Non Bearing turbo, what will be the difference? as for the All the other spec are same i.e. Housing, turbine...etc

1) Will billet be more heavy or Cast heavy
2) Will Billet provide faster spool
3) Will Billet Push more Air


Please let me know what is the what is the different iterm of Spool and performance..

as I like to turn my Greddy 20G to either Billet or Cast for the 60-1

spdracerut

iTrader: (2)

If the blade geometry is exactly the same, absolutely no difference.

gtm_maxwell

wow. understand, than there are not need to spend extral money on the billet Wheel.. Thanks for the infor...

ScorpionT

iTrader: (1)

The billet will spool quicker. Billet compressor wheels being used by Precision, Forced Performance, etc... have better aerodynamic designs than most older cast wheels, so along with being lighter weight for better spool, you also get improved airflow.

spdracerut

iTrader: (2)

The fact that it is billet is irrelevant. Now, if it has better blade geometry, then yes, it'll flow more/be more efficient, etc. But the fact that it is machined instead of cast is not a factor. Pretty much the only difference is surface roughness and even then, it's pretty much insignificant.

If you think otherwise, provide facts.

Geoff Raicer

iTrader: (7)

thank you soooo much for posting on this forum

03whitegsr

iTrader: (8)

I could be wrong, but billet aluminum was initially used in production turbochargers to keep the wheels together at very high pressure ratios in diesel applications as it is stronger then cast aluminum.

The same reason Garrett uses the "boreless" compressor wheels.

spdracerut

iTrader: (2)

The 'boreless' design is stronger than the typical 'thru-bore'. Makes sense as you don't have a big hole going all the way through.

Regarding a piece of billet, how do you think it's made? That's right, it's CAST. So if someone can explain to me the difference, and magnitude of difference, between a huge chunk of metal that is cast, then cut into a wheel, and a wheel that is cast in the first place, go ahead.

If you start with a forged piece of billet, then it's different as forging is a process to strengthen metal by aligning grain structures, blah blah blah. Garrett does use forged billet on one of their wheels. One other example that I have seen of using a forged billet is an aerospace axial flow turbine wheel. They took a solid chunk of titanium and forged it to get the grain struture to flow the way they wanted to, then cut an axial flow wheel out of it. Pretty damn cool as you could actually see the grain lines in the forged billet. But anyways...

Do any of the other companies start with a forged billet? Not that I know of, though I could be wrong. But I haven't read as such.

gtm_maxwell

So which mean there are no a big difference in changing from Cast to billet if all the other items is the same right..

a1091156

Correct.

notstock88

Cant say it any better than this;

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

helical

http://www.youtube.com/watch?v=VVZLlLjHV2k

http://www.flickr.com/photos/sumalaya/

03whitegsr

iTrader: (8)

This is old, but I may as well respond anyway.

Typically cast chunks of metal are not referred to as billet. They are typically referred to as ingots. Once the material is mechanically formed, then it typically becomes regarded as "billet."

Mechanically forming the material cause dislocations within the lattice structure which induces residual stress that helps reduce further deformation. More importantly however, mechanical deformation helps close voids in the material and voids account for the largest amount of weakness in a material as they act like micro stress risers that concentrate stress at the local level. A void essentially acts like the tip of a crack. Once you have a crack formed, it's only a mater of cycles until it fails.

Cast doesn't always mean it's bad though either. You can also use a process called HIP which is a process that uses extremely high fluid pressures to essentially "forge" the material by applying hydrostatic pressure to the external surfaces. I believe most of the compressor wheels from places like Garrett and Borg Warner undergo this process along with being vacuum or pressure cast to begin with. HIP and vacuum casting both greatly reduce the voids within the structure which dramatically improve the mechanical strength of the material. More importantly however, these processes also greatly reduce crack nucleation sites which means the fatigue life of the product is GREATLY improved.

As a counter argument, forging induces a great deal of residual stress. Tension residual stresses can easily form cracks as well, which this is pretty typical in 7000 series aluminum that often undergo stress induced cracking. Also, forging alone doesn't always improve the material structure. You can forge the material into a cube and then machine a compressor wheel. In this situation, the material isn't going to have a grain structure that is beneficial. You could forge it into near shape though which would provide favorable grain flow. I have no idea if the BW forged billet wheels are just forged chunks or actually forged into a near net shape before machining.

Finally, I believe most modern turbines in aerospace are actually single crystal double or triple melt titanium. VERY cool stuff, but definitely not forged. Single crystal grow allows a nearly discontinuous material lattice structure which is extremely strong as it is nearly void free and "defects" are almost entirely limited to other atoms from contaminant. Considering the double or triple melt processing, contaminates are likely very low.