Look into using magnesium instead of aluminum for things. It is harder to work with and weld but it weighs about a third less than aluminum. I would use it in sheet metal or flat plate construction.
Magnesium does have drawbacks. It is more prone to corrosion but I don't think you will be driving your dragster on salty roads in the winter. It is more flammable than aluminum (yes aluminum burns quite well once you get it started, The British Navy learned this in the Falkland Islands ) and burns under water. Scratching it really good can set some alloys off. To drill those alloys safely you need to use a thick oil bath to quench the shavings.
EDIT:
you could go way extreme with a custom Ti crank
http://www.advrider.com/forums/showthread.php?t=649649