F1 does not use Ti for pistons, it is because of the added weight and the heat transfer. Ti. is 60% heavier than alum. so if you make a Ti piston it would need to be 60%thinner in every area which could really be hard with Ti as it has some machining challenges. If you made Ti piston the could get them to even only 25% heavier than aluminum the extra weight would require heavier wrist pins and also stronger rods, as the largest load that a "normal" rod sees is the force generated at high rpms to pull, accelerate, the piston back from TDC and the mode of rod failure is tension, i.e. the rod is pulled apart and of course if you are trying to run 19,000 rpm as F1 does that extra weight makes for additional weight needing to be added to the crank and block to hold everything together. So if you are trying to make a V8 engine that only weights 80 kilos you go with aluminum pistons, not that they don't have piston troubles, ask Micheal Schumacher. (I define a "Normal" engine as one that is not on big percentages of nitro as these engines typically fail rods in compression or they push the piston pin down through the rod!)
Ti is also a very poor bearing so you need to give it some type of coating to get it to live if it is rubbing against something. F1 is using lots of DLC, Diamond Like Carbon, coatings on Ti to get a living bearing surface. Also Ti doesn't like to transfer heat, which makes it a great brake caliper piston but a poor selection for engines.
