Sell your Explorer (which costs over $.60/mile to operate) and get some small, used, ugly econobox with a miserly 4 cylinder (that costs more like $.25/mile to operate) Explorers are great, but they really cost a lot of money, both to buy parts for and feed. Plus the modifications you will eventually want to make on your Explorer can easily run in excess of $15,000
Given your age, we would take all our "spare" money (and all but the basics should be spare) and invest it in school, present and future. Get the hottest computer (Pentium MMX, preferably Pentium II or even newer) you can afford with the newest software, especially C and Java, and learn to program these languages. Take any available money and put it in a growth stock fund until you graduate from High School, then wait for a market high and get out with the money invested in a BBB-grade bond or preferred stock fund (about 8.75%) to provide income while you are in college or trade school.
If you are headed to college, consider this: Double major in college, that is do a full major in something you love (e.g. Art, Photography, Music Classics, History, Anthropology, Biology) and do a full major in something that will always provide you some good income (e.g. Business, Computer Science, Engineering). It will take you 4 years plus one additional semester.
If you intend to be an automotive mechanic, you still need to invest in the training such as Community College, including the computers, to be a good one these days. After this you will need to apprentice and maybe work for a specific manufacturer or dealership. You will be a step up on most toward building and modifying any fine vehicle.
When you get a decent job after all this, you need to save up one full years salary as a reserve. You need to begin to buy a place to live on your own before you buy toys. At the same time you need to be funding an employers retirement fund (e.g. 401k). If you are already working, even at a low paying job, you need to begin a Roth IRA. Fund the entire $2000 per year into your IRA and invest it into a growth stock fund...several after 10 years to spread the risk in several stock funds.
Here's your choices...you can have a really cool Explorer now that will probably be in the bone yard in 10 years and you will be $25,000 poorer and searching for your next "toy" car or you can be a millionaire+ at age 40 and buy any car you want. Go to Costco and buy a book called "The Millionaire Next Door" and read it cover to cover if you don’t believe us.
We’re not your mom or your dad or your guardian, who you probably don't like to listen to anyway. Yeah, we know we have *****in' Explorers...but we’ve "paid the price" and I don’t mean money…
Sorry to sound so practical, but these are the best modifications you can make at your age…right now...If you are not convinced or are already dripping with money, then by all means start building. Any modification will do wonders.
"The preceding statement has been endorsed by grouchy old farts with thin wallets and big payments."