JusMX141
Moderator
- 15,152
- 1,268
- Dec 13, 2005
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Greensburg,
Pennsylvania
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.
Anywho, here's some cast vs. billet compressor facts for you.
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.
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:
^ 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.
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.
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.
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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:
You must be logged in to view this image or video.
^ 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.
You must be logged in to view this image or video.
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.