sorry what's a so-signer? there's so many reasons why you shouldn't do it.
1. i doubt you have a steady job. if you lose it, you'll lose your car, and the cash, everything gone.
2. at 17, do you have a licence? you have either just obtained it, or you don't even have it yet. you have such a high risk of crashing it's not funny. it's dramatically reduced after a couple of years, which is why you should buy a **** car to start off with, then buy a better one later
3. as above, insurance. you got another $3,000 a year for that?
4. will insurance even cover you, considering that the car is illegal for you to drive? insurance companies will do anything not to pay out - so if you do crash, which you probably will, your car won't get paid out, and you'll have to pay for the other person's as well. i'm not 100% on that but you should really check it out, you could end up getting ****ed in the arse if you're not careful.
all the risk for what... so you can show off to your mates...