To improve upon a design from the late '80's perhaps?
I think the problem is the confusion over what you mean by "improve." Using this term implies that there is something wrong with the aluminum in the first place. I can only imagine these two scenarios:
A.
You are concerned that the alumuinum alloy used in your NSX has degraded in strength in some way.
Evidence of such degredation would be in the form of bends, stretching or cracks in the metal. Have you noticed any such defects in your NSX? If not, then the only way to test the "strength" of your alloy is to subject it to lab tests. Unfortunately, this means sacrificing pieces of your NSX to science.
Let's use your suspension and subframe components as an example. These pieces are made from a 6061 T6 alloy, which is composed of mostly aluminum, magnesium and silicon. The "T6" designator indicates this alloy is subject to heat tempering to increase strength. In order to be certified 6061 T6, the alloy must have a tensile strength in excess of 42,000 psi and a yield strength of at least 35,000 psi. In order to find out of your alloy has degraded, you would need to cut a piece out of each component and place it in a testing apparatus designed to measure these forces.
Assuming there is a degredation, it is unclear if heating these components back up will do anything. The heat tempering process is a very carefully controlled system that is implemented at the time of forging. Throwing the pieces back in the oven after 20 years is not the same process. I am not a metallurgist, but to do it right, you would have to melt down the alloy, re-forge and then re-temper. basically, you're resetting the molecular structure of the metal back to Day 1.
B.
There is nothing wrong with your NSX. You just want to make it "better"?
I'm not sure I understand this, but I'll give it my best try. For some reason, you think the various alloys used in the NSX are not good enough for your purposes. Perhaps you're feeling a lack of rigidity? Though, your car is a coupe and is street-driven, so I'm not sure how you could notice this. Or perhaps you think the car is too heavy and/or not strong enough to handle the increased power of your planned engine mods? If this is the case, then I don't think there is any way to make your alumium "stronger". Instead, you need to use new materials. Let's look at some options:
Side sills, suspension and sub frame:
6061 T6 Aluminum --> Ti 6-4 Titanium These are the compnents that undergo the most strain and consequently are built from the strongest alloy in the NSX. But, it's clearly not strong enough for you. Therefore, I recommend going to a Ti 6-4 titanium alloy. This is a weldable, workable alloy used in many industrial and aerospace applications. It is 90% titanium, 6% aluminum and 4% vanadium. You would need to have molds made of all your 6061 parts and then have them cast in Ti 6-4. While it is about 50% more dense than 6061 aluminum (4420 kg/m3 vs. 2700 kg/m3), it is still only half the weight of steel yet provides a colossal
140,000 psi tensile strength! I think this should more than serve your purposes, plus provide unassailable bragging rights on Prime, the rest of the internet and at cars and coffee gatherings.
Unit-Body:
5182 Aluminum --> Ti 6-4 Normally, I would say stick with the aluminum here, but since it must be welded to your new titanium side sills, you need a Ti unit-body. You would also gain the benefit of increased rigidity due to the higher tensile strength of the titanium. Finding a facility to re-cast the unit-body will be...challenging.
Outer Body Panels:
6083 T4 Aluminum --> Autoclaved Carbon Fiber To offset the slight weight gain from the titanium frame, I would go with a full autclaved dry carbon body. Not only would it be extremely lightweight, you could go for that racy CF weave look anywhere on your car, or even the entire car! In your case, however, it would be the real deal, further enhancing the brag factor.
All in all, if option B is your goal, I think this car could be done for around $5 million US. Just think, combined with a sufficient twin-turbo system (I think a maxed out SOS system is appropriate), Toda dry-sump, carbon ceramic brakes, Kakimoto exhaust, solid copper radiator and CF wheels (black, of course), you would have THE BADDEST ASS NSX ON THE PLANET. No one could challenge your car anywhere on the internet or at any streetlight from Oakland to Osaka. Prime members would be reduced to drooling vegetables at the mere sight of your NSX. Awesomeness.
Or, you could just accept that your NSX is awesome and respected the way it is and being made out of aluminum is pretty cool in and of itself. Just sayin'