Changing bits or adding other mechanical devices is not the answer. This is an unbroke horse and the fact that he came from the track makes things much much more challenging. This horse needs to be restarted like a green colt because that is what he is. He knows nothing of domestic riding and basic domestic riding cues will make him bolt as he doesn't understand. He is lacking in confidence and has a great amount of fear. And he is three. Your trainer obviously is not someone who has enough knowledge in working with this kind of horse, and there aren't many people who do, so it is not a criticism, just a fact. If you want to learn, you can try Clinton Anderson's Colt Starting video. It won't make you able to start this horse, but it will help you learn some understanding.
Forget about lunging, it will only make things worse. The last thing you want a race horse to do is get all worked up and running around in circles (what he has done all of his life) will be horrible for him. A bigger, badder bit and tying his head down is only going to make this horse go nuts. Tying his head will make him stronger in his neck and he could go over on you. The absolute last thing you should do is tie this horse's head down in any form or fashion. And anyone who tells you this is a good thing to do doesn't know what they are talking about.
Get some proper help before there is a disaster with this horse. It is shameful that you would "jerk his face off" as it just shows how little you know. How terribly sad and unfortunate for this horse. It is not about the bit. It is about training. Without proper training, a basic foundation, lots of ground work, there is no hope of getting real change and you could wind up in a wheelchair or dead. You have to gain this horse's trust and respect or you will never win him over and he will just be another lost cause. This is a typical story that I hear until it makes me ill. These horses are not easy and take someone with a lot of advanced horse handling ability and knowledge to help these horses become riding horses. This is a dangerous situation. It is not his feed, it is about training. There is nothing else you can "blame" this on and everything you have mentioned is not even in the ball park of identifying the real problem here. Again, makes the situation even more fear provoking and likely to meet with total failure. You have to change your way of thinking. You have to learn how to speak to this horse and it has nothing to do with saddles and food and tack. I have worked with these horses for over 12 years and this horse needs ground work and basic foundation. You should not even be thinking of getting on his back the way things are at present. It is frightening that no one around you is aware of this. Again, don't get hurt. It is not worth it. You have to give this horse order and do things in a proper progression. You not only have to teach him what is correct, you have to help him get over the horror that was his past life on the track. These horses are really abused so getting them to come around to be a domestic riding horse is not easy. I hope you get some help for this guy. Be patient and kind and respectful of him. He needs that more than anything. These horses usually have no use for humans so it is a tough proposition, but even worse when you don't know what you are up against. Think about it. You are not going in the right direction.