Well DSM, a few years ago this was my world and there were plenty of quite substantial companies who we brought in to sponsor National level motor racing.
I'm afraid there's no secret. It's VERY hard work and it's a bit like riding the Grand National; just 'cos you've cleared the first 25 jumps doesn't mean you'll clear the last one.
Now let me offer a tip. If the Guy Edwards book is still in print it's well worth reading as a good guidebook to sponsor-chasing. However much it's selling for. But even Edwards couldn't get blood from stones! About nine years ago I took a young driver to hear him speak and Guy looked very tired and frankly a bit emotional and that was at the time when his best efforts couldn't keep the Lotus brand in Formula One.
Let me also offer a bit of very necessary devil's advocacy.
Why on earth should anybody be interested in paying for you to go motor racing? Why, SSC, should they enquire about your proposal? What's in it for them? You simply have to approach the problem from the other side. Why [and you put your head above the parapet, mate, but don't take this personally as I bet everyone else here is as blinkered and selfish - or focussed if I'm being polite] should any company want to pay to see it's name in a motoring magazine?
Think broader, broader, broader. Think what the company might want from a sponsorship. Think what you need and think how you can broker and arbitrage bits together.
Here's my tip that not even Guy Edwards ever mentioned [possibly never even thought of it himself]
The car [the driver, the race]
is just an excuse for talking to people.