I would try using 1 PC to start with. I've worked on a project that runs 7 screens using only one PC (3 video cards and 2 RGB splitters) with no slowdown. But only one of the views was fully 3D.

If you scale up to the 3PCs, keeping them in synch shouldn't be an issue. Do some reading on network code in the user manual.

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Also look into using a force-feedback wheel. You can get an okay one for under $70 but, if you have a budget, you can get a pro-wheel for a few thousand. Even simple feedback makes a *huge* difference in car simulation.

If you are doing this with very limited cash, you might be able to buy a cheep XBox wheel and attach a real car wheel to it somehow (you can buy one at your local auto-parts store).