Ouch...that sounds harsh... I feel for you, I really do. I was kinda the same (except for the homeschooling scenario and that I was into computers rather than cars). I ended up sneaking about behind my dad's back to fool around with computers.
I think it's really unfair for a parent not to support a child's interests. I mean, yea, surely a turbo can be a bit more dangerous but, from what I can gather, it's due to your interest that you want it and not due to wanting to be irresponsible or reckless.
Parents do tend to think they are ALWAYS right...but at the end, they know just as much as the next person. I have quite few problems in my life, including social ineptness, due to my parents not listening to me (which they still don't). Yet, they are not perfect either and blaming them for it won't help any.
A parent will always want what they think is best for their child...but that would a lot of times be what they as a person would have wanted when they were a kid and not necissarily in line with your personality/interests.
In the end I became a programmer...much to my dad's dismay. And now, guess who has to help him with their companies software that was written by an ape and which they refuse to replace?...you guessed it...me!
Heck, I don't even charge him for my time. Just seeing him begging me for help is enough
The other thing that I have found...and this is very important...is that parents tends to try and stay away, and subsequently try and keep their kids away, from things they don't understand. For instance, my dad never really and still doesn't understand precisely how a pc works. That's why he didn't want me to mess around with the computers at home when I was kid... He was afraid I would brake it. Then later on he said there is no future in computers...ummm yea dad...that's why Bill Gates is a billionaire and why I am driving a 2L Mazda 3 and not a rinkedink 2nd hand toyota tazz/vw city golf.
Strangely enough...I also mess around with composing a bit. I have a talent for playing music by ear but can't read sheet music for caca
. Haven't done a lot though due to wrist problems.
I don't know how to help except to say that once you get older and are able to be more independent you might be able to shed some of the shackles. The other alternative is to somehow, find a way to get into family counceling or some such. I know my parents was also highly irate about shrinks and that stuff but eventually they were forced to get me to a shrink...the details of which I would rather not discuss under these circumstances.
They will however never really change. After all, in their opinion, it's you that has a problem and not them and they feel that they have been living for soooo long like this, why should the change now.
It's never too late to start learning a new trade, so even if you are only able to persue your dreams once you are older and out from under your parents, there is always still hope.
I hope I didn't rant and ramble your ears off and that what I said helps, even in the smallest amount.