Aluminum isn't that much better than steel as far as strength to weight ratio goes, and I think it would be hard to bond it to the steel properly. Well thought-out crossbraces and fiberglass floorboards might work though.

 

would have to talk to my old boss about that one that might be a good idea his car is in the 7s in the 1/4 mile
he built it $80K car with 850BHP only uses gas no nos or superchargers

next time I talk to him I will ask and post it on here

 

The only reason for the aluminum is because it is easy to work with to replace the sheetmetal after you ripped it all out to install the cage, rear tubs, frame braces, etc. Also allows you to have removable panels inside the car for easy transmission access, etc. Plus it looks nice if you aren't putting an interior in your car. If you are looking for reinforcement the aluminum panels won't do it, but if you just want the look then go ahead.
greg
71 240z

 

Greg's right

The aluminum floors in race cars merely seal off the tube frames to keep stuff in or out. They usually don't provide any stiffness. However, aluminum does have a great strength to weight ratio when used properly. Before composites were widely used, aluminum ruled for monocoque race cars. You have to tie the panels together with alot of rivets to spread the load out, but if you do this with alum to steel, you're asking for trouble. If you want to lose weight here and fix your floor, you can weld in some steel crossmembers and attach a non stressed panel that merely seals the opening. You have to make sure your design is at least as strong as stock too. If you've got a rustbucket and are handy with a welder, it might not be too bad. Otherwise, it will probably be quite expensive.

 

RE: Greg's right

well i was just curious. the advantage i thought would be the fact that aluminum wouldn't rust, and in new england thats a plus.

i was talking to the auto rust people, and they said 500-600 labor to change the floor on one side, plus another 100 for the floor. a while ago people were saying 300-400 for a whole floor to be put in, so does the auto rust thing seem high.
the car is pretty solid, but the driver floor is getting bad, no big holes yet though.