I'll give a hearty second to Todd's comments on Aluminum subframes. I've watched Todd and other hillclimb racers struggle with the Wells Coyote Aluminum tubeframe hillclimb cars. Despite being constructed from high alloy tubing and using good quality TIG welding, they suffer from bending, fatigue failure, and cracked welds.
I've been through the strength of materials issues between Aluminum and Steel both here and on Topica TechSHO, and frankly, I'm tired of repeating myself. Do a search on either list and read what I've written.
One of the problems with welding Aluminum is that the heat of welding de-tempers the local area around the weld. To achieve ultimate strength with welded aluminum, the entire subframe would need to be heat-treated after assembly. Then it may need to be straightened, because the heat treat may cause it to twist up a bit.
Ownership of a TIG welder and a tube bender does not qualify one to build SHO subframes. Do you possess the tools to perform a finite element analysis to understand the high stress areas and bending moments of your subframe? For the individual proposing the integrated subframe/subframe-connectors/rear-torque-box reinforcement package, do you have the crash simulation tools and supercomputer needed to evaluate your design and its effect on the crash-worthiness and occupant protection of the vehicle? You'd better have these tools, and/or one heck of a lot of liability insurance, because if you screw-up, people are going to be injured or killed, and no amount of slickly-worded liability disclaimers are going to keep your butt out of court.
And those of you who talk with authority about tubular K-members for Mustangs, how many of you self-professed experts actually own a Mustang tubular K-member, or have done extensive research on these pieces? I have, and if I were to put a tubular K-member on my open track SVO Mustang, I'd consider only Griggs or Maximum Motorsports as potential vendors. I know these people have done the research and engineering to make a K-member that will withstand the forces of road racing. Everything else is potentially under-engineered, light-weight-at-any-cost, drag-race-only junk.
On the subject of the U of Wisconsin Aluminum Sable project, kindly download this pdf which summarizes their efforts in 1999:
U of WI Aluminum Cow, 1999 Technical Report. Please refer to page 9 where they speak of their Aluminum engine cradle (subframe). FWIW, they address the heat treating issues I spoke of earlier. Now, for a 1G (10m/S^2) lateral cornering load, they're willing to put up with
3 TIMES the deflection of the steel engine cradle. That may be considered acceptable for a street car, but this part won't get near my track SHO. Additionally, for Aluminum, flexure = fatigue, and fatigue = eventual failure. Somebody write these folks a letter and ask them how many miles they have on their Aluminum Cow? I'd speculate, perhaps a few thousand? I'd like to see a full report on their Aluminum engine cradle when they've racked up 50 or 60 thousand miles.
<small>[ February 29, 2004, 03:04 PM: Message edited by: Gary M. ]</small>
