Electric cars don't typically need as much HP, unless they want a high top speed. We'll be happy with 70 MPH. Electric cars have an enormous amount of torque though, and it is available anywhere in their RPM range, so they come off of a corner fast and get to their top speed fast. We're targeting a peak HP of 50.
The rest of the math is mostly correct. Our Sam's Club deep cycle batteries had 96AH at 12v and we could get about a half hour out of ten of them without discharging them very deeply.
Like about everything else, the big challenge is going to be thermal management. I've been digging through technical specs on batteries, controllers, and motors, and none of them are really suitable for endurance racing, which is hours of always being at full throttle or full brake. That's why when you take a Tesla to the track, you get about 4 laps out of it before it gets too hot and you have to stop flogging it.
What we found with our car is that you have to drive it like an extreme hyper-miler in racing conditions. Luckily one of our drivers has a hybrid as a DD and is in to hyper-miling, so he figured it out quickly. We developed four rules that allowed us to keep it out there:
Never drop below 30 MPH
Never exceed 40 MPH
Never exceed 100A current draw
Never use the brakes
Now we just need to upgrade the 35 year old powertrain so it can handle roughly double the current number with occasional 400A bursts, and lighten it while upgrading the suspension and steering so we can carry more speed in the corners. Having to stay full track right because we are so slow also hurt our momentum; if we could take a decent racing line then we could also be faster and more efficient.
Everybody grab your brooms, it's shenanigans!