[RGlasel]

I have a vintage car repair shop at my disposal

Promotional materials for new cars are chock full of composite and highly processed (and very unrealistic) photos; with the use of appropriately coloured drop sheets, the garage is the perfect place to shoot a car in isolation. High ceilings, few windows or mirrors for unruly reflections, the ability to eliminate bright ambient light and unwanted onlookers, even having cleaning materials handy, these are all advantages to using the garage as a studio. When you have the car shot perfect, drop it into whatever background you want. Use whatever flash you want, but automation is only going to get in the way.

Actually, he's better off painting with the Pentax 540.

Because its flash is so much brighter, he can really stop down the camera for the composite and kill the ambient if needed. Onlookers can be removed … there just needs to be a single frame where they're not in the same position.

Tripod and permission from the owner required … in fact, the owner could be sold resulting photos!

He can do exactly that. Different than light painting with a constant source in a controlled light environment. He said he had a space for the cars, his cars.

[clackers]

He can do exactly that. Different than light painting with a constant source in a controlled light environment. He said he had a space for the cars, his cars.

Yeah, re-reading the OP, I think they're other people's cars, so he has a market not just documenting for the repair shop, but selling prints to the owners!

[gerax]

Yeah, re-reading the OP, I think they're other people's cars, so he has a market not just documenting for the repair shop, but selling prints to the owners!

You got that...

[gerax]

So, shooting technique and polarizer diatribes aside what about the speedlight model?

[RGlasel]

what about the speedlight model?

Use whatever flash you want, but automation is only going to get in the way.

I should have added you need flashes with multiple power settings that can be triggered off-camera, with enough power to be used with a flash modifier.

[photoptimist]

You can solve or at least reduce flash reflections off chrome, glass, and shiny paint by polarizing the light from the flash and using a polarizing filter on the lens to block directly-reflected hotspots. See Get Amazing Flash Photos With a Simple Polarized Flash Modification.: 6 Steps for instructions and sample photos.

P.S.: you'll get best results with a high-quality polarizing filter and film materials. Cheaper polarizers will tend to produce blue or brown hotspots.

P.P.S. Old laptops, tablets, and smart phones tend to have very high quality polarizing films because that determines the quality of the black levels of the LCD display. A bit of scavenging and careful peeling of the film can yield a decent sized piece for putting over a flash.

[Digitalis]

I have no experience with setting up lighting, but I have taken a lot photos of cars in museums. One of the biggest problems I've seen is specular hot spots on the shiny paint (mostly reflections of the spot lights used in the museum). I try to move my angle around to reduce the worst of them

The pros remove those in post, standard routine in that line of work.

It is better to eliminate those points of specularity in the first place, post processing is a necessary evil with all forms of commercial photography. Relying on PP when you can achieve excellent results in camera in the first place is preferable.

His solution, a white tent big enough to drive the trucks into, Huge banks of rented lights positioned outside the tent using the tent as a huge diffuser.

This is pretty much how you do it. Use Big Light diffusers! as they reduce spectacular reflections - I have worked with softboxes bigger than most cars when I have done commercial automotive photography, At one point I used an aircraft hangar to photograph a cut away jet.

A simpler approach (and less expensive) is using Bounce flash - all you need is a large white (or near white) surface, ceilings are very useful here. Big softboxes are extortionately expensive. Avoid un-diffused direct illumination at all costs, as it will only increase specularity. As mentioned above: Polarisers cannot remove reflections from metallic surfaces but the polarisers effect upon glass windows,tyres and other non-metal surfaces on a car cannot be ignored.