When it comes to insurance, there are only two kinds of performance cars: those that are driven only for shows, and those that see street use, and even street racing. Because show cars are generally stored in locked garages, hardly ever driven, and are usually antiques or other collectibles, they're actually easier to insure. After all, most specialty insurers will write policies even on modern muscle cars, as long as their requirements for use and storage are met.
Performance cars that are actually expected to "perform," however, are a bit more difficult to insure. These cars tend to be driven hard and fast, at high speeds and high RPMs. They're often parked on the street, driven by younger, less experienced owners, and almost always sport modifications, from minor things like alloy wheels to engine and exhaust mods, to full-body kits. The good news is, performance tuning is becoming more and more popular, and since more hobbyists means more cars in the insurance database, getting coverage for a customized car, while hardly simple, is getting easier. When you begin shopping for car insurance you'll probably want to begin with the company that currently holds your policy, even if that policy is based on a car that has no modifications." If you're already in good standing with you, they'll be more likely to continue that relationship, especially since insurers generally make money on long-term clients who continue to renew their policies than they do on new customers who are often accepting special introductory offerings.
There are also two very specific things you can do to help make yourself look like a better risk to your insurer. The first is to reduce your risk profile, and the second is to always disclose your modifications.
Reduce Your Risk Profile While nothing you do can change the way your insurer will look at your car, especially if it has a performance engine, but you can be sure they see you in the best light. This means never getting a ticket - ever. It also means never speeding in residential areas, never driving while intoxicated, never being anything but conscientious behind the wheel. It's also a good idea to take defensive and performance driving classes, to help you hone your expertise at handling a powerful vehicle, especially when there's inclement weather.
Disclose Your Modifications Even if all you've done so far is upgrade the stereo system, if you're customizing your car, you need to be explicit about any changes you've made, and any you plan to make, when discussing your insurance coverage. You should provide part numbers, part descriptions, and estimated cost to replace them, and if you can, you should also provide your insurer with sales listings of cars of the same make, model, and year as yours, with similar modifications, preferably being offered at the same price that you believe your car is worth, or more, and, ideally, these cars should be in worse condition. Not only will this help your insurance company accurately value your car for coverage purposes, but in the event you get into an accident serious enough for the car to be totaled, it will help ensure that you are adequately reimbursed. There is another reason beyond coverage amounts to be certain that you disclose all modifications, however: if you don't, your coverage may be voided. Finding insurance for a customized car isn't as easy as insuring a fresh-from-the-lot SUV or sedan, but with patience, perseverance and preparation on your part, you can find coverage for that really performs for you.