Exposure, exposure, exposure.
Sponsorship is all about marketing for the company that sponsors anything. Year One puts together goodie bags because everyone carries it around plus their splats tucked inside. Windshield banners, pens, frisbees and so on all carry the name in the hope that a person's need can be met, spur of the moment, when they look at the item with the companies name on it.
The mutual benefits are assumed - but should be mentioned anyway. What the companies are looking for is an understanding, on your part, about the real (and imagined) benefits that you will get from a partnership. Anyone can write out a check to you to go buy parts - why should they do it?
Exposure, exposure, exposure. Is this a full time job for you? How many races will you be in this year? Where are they being held? All of this demonstrates the demographics of the crowds that will watch the race. Any chance for TV exposure? If they gave you an extra $500 for painting supplies, would you plaster their name across the hood?
Who else has alrady agreed to supply you? (big, big, big - no one wants to be the first one on the car) Success breeds success so if you've won races, and been interviewed by motoring press that actually gets read by the everyday driver, have you thanked your sponsors openly?
The more you win AND whore your sponsor's name, the more likely you'll find other sponsors willing to write a check.
I bet you're saying: well yeah, doh! How do I get in front of a sponsor? Then how do I construct my presentation to get to the next step - business planning? Then finally, who should I have with me when working out terms and conditions of the sponsorship / partnership?
Those are good questions, unfortunately I don't know racing like I know software. But I bet if you look professional, demonstrate your understanding of the business side of racing (marketing benefits) and you can clearly show a chance of getting good exposure to the masses (whether you win or not) then you will be in a better position of making it to the second discussion.
Don't be afraid of reaching out to non-traditional sources of sponsorship. Exhaust shops, body shops, aftermarket parts suppliers are all the companies everyone else goes after. What about the tools makers? Paint suppliers? Banks? Any other company a normal human being might turn to for... something. All companies are looking for is effective marketing and they know they have to pay for it. Don't just go for free parts - go for the money and simply buy the parts (hopefully discounted through a separate partnership / sponsor who's terms involve getting parts at cost).
If you start thinking like a pee-wee football coach or soccer coach who has to go out and get a sponsor to help defray the cost of uniforms for the kids, then you have the right mindset. Just be ready to talk about how both of you will benefit from such a relationship.
One last thing - don't wreck the damn car. You can't win that way and more money goes into more parts. How's that for obvious?
Good luck man. We're pulling for you.
, but ended up with this - 
for free. Can't argue with free.
