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Billet / Machined Compressor Wheel Facts

Posted by JusMX141, Jun 17, 2020

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  1. JusMX141

    JusMX141 Moderator

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    Starting a thread over this because I'm tired of arguing with people who think all billet / machined compressors are an upgrade. The general public is often clueless yet will continually debate something they know absolutely nothing about- I had a guy earlier this week argue with me on another public forum that prior to the GTX lineup Garrett used cast steel wheels in all their turbos. That's right...they all had steel compressor wheels. :rolleyes:


    Anywho, here's some cast vs. billet compressor facts for you.
    • Cast is cheaper to produce and can be made in large production runs for turbos that are produced in massive quantity. This is why *most* factory-equipped turbos you find will have a cast compressor...the manufacturer just doesn't have the 2 hours to wait while a CNC mill carves out one of 20,000 billet compressor wheels needed for a Dodge Dart. Of course just like anything else, there are exceptions- mainly referring to machined wheels found in production turbos used in extreme environments.

    • Billet is stronger than cast due to less air pockets in the raw material.

    • Billet is heavier than cast due to less air pockets in the raw material.
    Whaaat? Heavier? You heard that right- when comparing two compressors of identical size, shape, and blade design the billet wheel will always be heavier due to the density of the casting. The only thing you'd stand to gain will be durability- you will often lose spool and response unless the compressor in question is a performance revision.


    Just for reinforcement, here are three MHI 18KX3 compressor wheels...one in OEM cast, one in OEM billet, and finally an aftermarket drop-in performance billet version.

    20200617_121205.jpg
    20200617_121118.jpg
    20200617_121250.jpg



    So the performance revision saves 20 grams of rotating mass over stock cast...pretty impressive on a 55mm compressor. How is this achieved? Well it's done by taking most of the strength out of the wheel and relying a lot on the structural benefits of the billet raw material. That's fine & dandy but if it's not done properly it can cause the wheel to fold under stress and collapse, causing a catastrophic failure. So by adding distance to the blade from the center of the hub but also reducing the hub thickness to get maximum blade exposure you're now trying to carry a sheet of plywood in a windstorm with your fingertips. This puts a lot of stress on other areas of the wheel, including the backplate:

    72200300_130729444971447_2829555099196456960_o.jpg
    ^ That "ripple" you see in the backplate of wheel is a tidal wave of destruction- the compressor wheel is getting ready to fail. The blades are yanking on the backplate of the wheel under load and have caused it to distort indicating this bridge is about to collapse. The scary part is that's not a no-name Chinese compressor wheel, either.




    So choose your billet compressor upgrades wisely- buy from trusted vendors and not just whoever has the cheapest price because 1) you may not be buying an upgrade at all, and 2) what you're buying may be garbage by design. Don't always buy into the "if it's lighter it must be an upgrade" hype because if it wasn't designed correctly it's not going to last. Your best bet may be a design revision that gives you some decent efficiency gains but isn't necessarily a massive weight savings.
     

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    1998 Mitsubishi Eclipse GST
    manual · 2G DSM

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    1997 Mitsubishi Eclipse GSX
    awd · manual · 2G DSM

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    1992 Eagle Talon TSi
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    1993 Eagle Talon TSi AWD
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  2. jed344

    jed344 Supporting VIP

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    I have tried for years to argue this same point to the diesel crowd back when I did diesel stuff. Just because its shiny does not mean its better.
     

    1K  38

    1997 Mitsubishi Eclipse GSX
    awd · manual · 2G DSM
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  3. 1qkfwd

    1qkfwd DSM Wiseman

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    Diesel guys are horrible for going straight to that whole billet wheel hype.
     

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    1992 Mitsubishi Eclipse GST
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  4. bastarddsm

    bastarddsm Proven Member

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    ^ You ought to see the sh** we run. 5 blade 76mm smooth bore, blades are 0.0150" thick We run a filter and it's still comming apart. but it's 200hp over a more pedestrian wheel, and this lives it's like 300ft at a time 15 times a year LOL.
     

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  5. Ludachris

    Ludachris Founder & Zookeeper

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    If you think about the psychology behind purchase decisions, it's not surprising. The billet wheel turbos have always been heavily marketed as an upgrade to comparable non-billet options. The combination of marketing language and the secrecy surrounding design specs for the marketed products and those they're being compared to makes it pretty difficult to determine how much of an "upgrade" they really are - we all know that comparisons aren't always apples to apples when it comes to marketing. Naturally, as a result, the assumption is that all billet wheels would be upgrades.

    Thanks for trying to shed some light on this Justin.
     

    Street Build 9K  0

    1997 Eagle Talon TSi AWD (sold)
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    1991 Mitsubishi Eclipse GSX
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  6. JusMX141

    JusMX141 Moderator

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    A key benefit of billet is now smaller performance operations can have small runs of their own performance-designed wheel generated without the cost of getting 1,000+ of them cast. The CNC mills just know what you tell them, they can make one or 10,000 of the same piece. The next time I have something like a 68HTA pulled apart I'll compare the weight of one of those wheels to a comparable cast MHI compressor like the 18G just to see where it's at in regard to rotating mass. There are other factors that determine spool and airflow production aside from just the mass of the wheel alone, however.
     

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    1998 Mitsubishi Eclipse GST
    manual · 2G DSM

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    1997 Mitsubishi Eclipse GSX
    awd · manual · 2G DSM

    3K  0

    1992 Eagle Talon TSi
    manual · 1G DSM

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    1993 Eagle Talon TSi AWD
    manual · 1G DSM
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  7. ist dwa

    ist dwa Proven Member

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    Buy FP turbos and let Robert worry about what is best. Problem solved.
     
  8. bastarddsm

    bastarddsm Proven Member

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    While some of them kick ass. He's produced some straight garbage over the years, and sold it as the "best turbo ever".
     

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  9. Sniffbooger

    Sniffbooger Proven Member

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    Good information... I'm considering upgrading my Chinese 16g to a nice 6 blade Billet 20g with a 9 blade exhaust wheel...there's a company in Taiwan called TRITDT making these for under $800...and also MAMBA....wonder if they are any good... Taiwan manufacturing usually has higher quality control standards than the Chinese junk...
     

    Street Build 292  8

    1998 Mitsubishi Eclipse GST
    fwd · manual · 2G DSM
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  10. JusMX141

    JusMX141 Moderator

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    Great things have come from FP over the years, but I never like to blindly put all my eggs into one basket.

    Turbo Tuner Tools is just a distributor just like Mamba, Arashi, and Kinugawa...so chances are if you buy a billet compressor from them it's just a rebranded "white box" KTS wheel and whatever turbine they can get their hands on. For now I've actually gone back to clipping MHI turbines as opposed to aftermarket 9-blades for reasons outlined here; I actually did exactly what you're speaking of for a customer about a month ago using a knockoff 20G as a donor core but it got a full new CHRA, KTS D635 compressor, and high-pressure actuator upgrade and I discarded all the existing non-spec China parts. Turned out pretty nice for what was invested.

    1.jpg 2.jpg 3.jpg
     

    3K  0

    1998 Mitsubishi Eclipse GST
    manual · 2G DSM

    6K  14

    1997 Mitsubishi Eclipse GSX
    awd · manual · 2G DSM

    3K  0

    1992 Eagle Talon TSi
    manual · 1G DSM

    3K  0

    1993 Eagle Talon TSi AWD
    manual · 1G DSM
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    delta448, Sniffbooger and 1qkfwd like this.

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