My advice would be to start karting 80 cc's then work your way up. From there maybe do a SCCA racer on the cheap - or buy a 944 and start doing DE and track events. Better yet - start doing the DE and track events - there are some instructors there that have 30 years of experience, some past SCCA champs. You can't beat that for $180.00 and car prep.
Then sign up for Chin and NASA and get on the track as much as possible. You think you are good - but really you don't know dick. There are guys I know that can pilot a washing machine around Sebring faster than me.
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"If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough horsepower"
-Mark Donohue