Open and Full-Face Helmets
Running a car with a windscreen has certain advantages over one without. The main advantage is the ability to keep some of the muck out of the interior of the car. Unfortunately the muck also sticks to the windscreen which, if the wipers aren't working too well, makes it very difficult to see. Conversely, running without a windscreen lets all the muck through; so you can see, but you're dirty and possibly very cold. Of course you can run either an open or full-face helmet in either type of car; however you'll need a good set of goggles running an open-face without a windscreen.
The Nolan helmet (Jet N41) is a relatively cheap open-face design that we ran in both the Datsun and Commodore. Being as both cars had windscreens, running a full-face helmet wasn't required. It was evident however, on several occasions, that a ventilated full-face helmet and no windscreen would've been a better option (e.g. when the windscreen washer bottles ran out of water or when the dust inside the car was thick enough to cut). But everything has its pros and cons... The purchase of the sans windscreen Rodeo forced a googles/full-face purchase decision, with the Bell full-face winning out because of the HANS posts.
The Bell helmet (Ultra series - Vortex FA) has both a forced-air inlet and posts for the HANS device. The forced-air connection is used to push clean air inside the helmet so that the wearer doesn't choke on dust and doesn't get grit in the eyes. The integral HANS posts (together with the associated brace) are designed to restrain the helmet (and hence the head) within a limited field of movement during an impact. This has the effect of significantly reducing the chances of whiplash and other neck injuries occuring (note that the posts cannot be retrofitted to an existing helmet). The air is forced into each helmet via some flexible tube from the Racer Imports supplied blower/filter unit.
Tear-offs are usually used to remove any dirt that accumulates on the visor of a full-face helmet (goggles have a similar sort of setup). These work reasonably well unless it's raining, when the water seeps between the tear-offs making your vision worse. Might be better to carry a small rag under these conditions. Whilst on the subject of helmet problems, you might want to keep an eye on the chin strap buckle, as the cheaper versions have a tendancy to rust. Also, small rocks thrown up by cars in front can chip the paint; however these chips can be repaired (for a price).
Note that any helmet will have to meet the appropriate Australian Standard (AS1698), or one of the other multitude of standards that are quoted within the Schedule D - Apparel section of the CAMS manual. The HANS tethers must also bear a similar FIA or CAMS approved label.
