So I am going to come off as an A$$ here, and I am probably going to get some nasty PMs from the leadership, but oh well.
YOU DON'T KNOW WHAT YOU ARE DOING!
You clearly don't know what goes into the design of these things, you're simply looking to make a part out of a "lighter" material then close your eyes and hope it will be okay. That is stupid and the kind of thing that gets people killed. If you don't care about yourself that's fine, but the part that flies off and hits another driver's car won't stop because he wasn't an idiot, and the rescue workers trying to cut you out won't be magically safe because they didn't redesign their nomex suits with much lighter polyester.
I'm not trying to be a jerk, but I am a mechanical engineer, I have actually designed fabricated knuckles for heavily modified, specialty vehicles before, I know what goes into these things. There is nothing wrong with making new parts (cue the amateurs built the ark, engineers built the titanic thing), but stop and think a bit. There are very knowledgeable people and forums out there who would be glad to help you come up with something, but you have to ask, and more importantly you have to listen.
Correct me if I'm wrong but wouldn't the exact same part in aluminum be lighter simply due to aluminum being lighter than steel? why would I have to measure the volume?
By volume Aluminum is lighter than steel. So is pine, but there is a reason no one makes knuckles out of pine. Strength to weight is a better comparison, and a key difference will include consideration of fatigue.....
@John hasler how does a weldment work? I've never really heard of those...
This statement scares the crap out of me from someone fabricating critical vehicle components.
@q20v I appreciate the response, I deffinetly don't have the sort of equipment for NDT. The auto manufacturers are cheap though they're deffinetly cast parts they don't even so much as clean up the parting line from the 2halves of the mold... I've already done away with all my bushings and my control arms are all chromoly tubing already the point here was to adress the only thing I haven't yet and that's the weight of the oem knuckle. There are options for my car but the parts cars needed to find the parts are hard to come by so I was exploring other options. I think i may be scraping the idea until I come across a parts car with the knuckles I'm looking for.
Casting in large volumes is cheap because over 10 million parts you pay for the cost of the hundred engineers that designed, prototyped, and tested the parts. You also pay for things like x rays and heat treatment. When you say that you are going to cast something and when GM, Toyota, whomever else says it, you are not talking about the same thing!
Also.... "chromoly" steels are great, they are also a PITA to weld, and like to crack when not welded properly. Just something to consider, but control arms becoming control sticks doesn't usually end well.