Why is it so expensive to add a teenager to a car insurance policy?

I have a Scion tC, and I’m looking to get some performance upgrades, but I don’t want to overextend my budget. Before I go all out, what is the Scion tC’s top speed?

My home is over 100 years old and most of the plumbing is made from cast-iron pipes. My preferred insurer now says that they won't offer coverage because of this. Can they actually deny coverage?

"I have always loved the C-10 Chevy trucks of the 1970s. However, they’ve gone way up in value lately and I would have to get a car loan to buy one. Another issue is finding one worth buying and getting the loan in a timely manner. How is this usually handled, and what is the best way to go about financing a classic truck? "