Should be fine in your portfolio but don't make posters or calendars from them. Don't send them to stock sites or in any other way sell them or licence them.
Check, if you can, the ticket stubs or websites of the car shows you've been to for any language about their photo policies to make sure they're not going to over-reach and claim something against you. While I say it's "over-reaching" and it shouldn't take a lot to prove editorial or fine-art usage, you're better off finding out beforehand if the event has a 2 paragraph release you can sign rather than paying for the lawyer's time to prove you're right.
Essentially, showing off your photos from that day is cool, but try to avoid too many pics of the event name, or sponsors etc, so nobody can construe that you're trying to make it look like you're an official event photographer or in any way that those companies are endorsing your skills.
Magazines are often invited along by the event, sponsors etc, or they may themselves be sponsors. Even when not, they are covered by editorial usage and are providing 'a service in the public good as a news outlet'. In some instances the event or a sponsor is paying for the photos and article in the magazine, so it moves into the realm of advertising and those contract terms.
I like making photos and sometimes I think I'm getting better... then I realise it doesn't matter. I like making photos!