Full face on a bike, definitely. But personally, for autocross or rallycross, especially in a car with airbags, I worry more about slamming my head on the windows, b-pillars or roof than smashing my chin, so the comfort of an open face helmet compared to a cheap closed face wins out.
On the track, go closed face. There's a greater risk of a crash involving a sudden loss of forward motion, which is when the closed face will protect you better.
I've ridden bikes with my Simpson bandit. The obvious complaint was the lack of ventilation. It got hot pretty darn quick.
In reply to Contradiction: A motorcycle helmet may be ok if it has a Snell rating like mine does.
The track I want to do HPDEs at told me an SA helmet is required. Looks like I'm going to go that direction instead. Thanks for the replies everyone.
Some SA rated helmets also have DOT approval - if it has a DOT sticker, then it's also been judged to have enough peripheral vision. The only real potential drawbacks are that motorcycle helmets often have better ventilation and washable padding. If you use it for riding a lot, you'll definitely want the washable liner. These seem rarer on SA helmets for some reason.
Sonic
SuperDork
4/21/16 9:55 a.m.
My first closed face SA helmet was also DOT approved, so I used it in the limited amount of riding I did as well. No problems.