Tank, Indy cars do run on street circuits during the racing season. I think that they are not equal to FI cars on those circuits. But for the rules, perhaps they could be. The engines are a little bit larger than the F1 engines but do not have electric boost.
F1 engines make somewhere in the region of 400 HP per liter. Indy engines make only about 325 Hp/liter. The difference can be assigned to the rules limited boost of the Indy engines. In most cases the Indy engines, whether Chevrolet or Honda,use the McClaren TAG 400i engine control module (ECM))
An interesting difference is that Indy cars do not have power steering while F1 cars do have that feature. The Indy driver had better be physically fit in order to wrestle that projectile through a race that may last for nearly 90 minutes. Not that the F1 drivers are not physically fit by any means. They are all athletes in their own way. Their capacity for assessing risk weighed against common sense is quite another thing.
Then there is the NASCAR engine. 5.9 liter pushrod, carbureted, beasts that make in excess of 700 HP. They are marvels of durability but they fall well short of the sophisticated engines at something like 130 HP per liter. Despite that, the cars that resemble ordinary passenger cars, can often exceed 210 MPH.
Americans are out of their minds about racing cars, motorcycles and racing boats too. North America is a big place but there are racetracks within an hours drive all over the nation. Those tracks vary in length from one quarter mile to three eighths mile to half mile in length, or circumference if you prefer. Actually almost all of them are oval shaped. Saturday night racing is a disease that pervades much of our nation. During the season there is a race every Saturday night at thousands of venues across America. The cars are of various descriptions and divided into classes.. There are big dollar cars that use powerful V8 engines and there are fierce competitors who race small cars, usually with a limit of 2.4 liter engines. Now and then the race promoter will have an event that races school buses. The more madcap race is the figure eight race that runs on a track that has cars crossing an intersection at the middle of the figure eight. We will race anything. Even turtles or cock roaches. Once in a while we will have an event that races riding lawn mowers.
Most of the Saturday nite tracks are asphalt paved. There are also many dirt tracks that are just as exciting and a lot dirtier than than the paved tracks. Among the premier dirt track racers are what is known as Sprint cars. They are open wheeled single cockpit cars with 700 HP alcohol burning engines, Some of them have wings overhead of the driver. They are incredibly fast. Most of them weigh only 1600 pounds (725kg). My local track is quarter mile asphalt, At least 50 to 60 competitors will show up with regularity. It can be said with some degree of confidence: American red neck racers are everywhere.
I do hope to learn that the Brits are not so foolishly afflicted.
I've been enjoying "In Our Time." Took a while to tune my ear back to the BBC English intonation (I used to go to sleep listening to BBC 4 but it's been a few years). Especially as delivered in perfect "reedy professor" by Melvyn Bragg. I initially subscribed to "History" and "Science" as well but now realise all that does is duplicate any episodes that qualify. Thanks again for the recommendation, Sir Albert.