Any modifications made to a vehicle change how car insurance companies price the premium. Performance modifications, including to the exhaust, strut bars, suspension, or engine, increase the premium.
Some insurance companies refuse to insure modified cars if they have expensive modifications like engine performance enhancement. In that case, you will need to purchase supplemental coverage or classic car insurance that is customized to your vehicle. Always speak with your insurance company before modifying your car. Not doing so compromises your coverage.