Article from almost 6 months ago about electrical assist and how to keep the sounds and V8's instead of pissed off vacuum cleaners and more in the article. Notice it is published on Nascar's web site. there's your first clue.
It’s time: The NASCAR hybrid
HYBRIDS DONE RIGHT
Back in March, I was at a fan event before the Las Vegas race and noticed that there were a lot of international fans in attendance. I wound up talking to people from Germany, Ireland and Australia — where, incidentally, the Formula 1 race season was about to begin. I asked them why they were in Vegas instead of back home, heading to the Formula 1 race.
“We don’t go to F1 races any more. We don’t like the cars,” they explained. “They don’t sound right. They’ve switched from big engines to small engines, and that made the cars too quiet. They sound like vacuum cleaners.”
That’s one of the factors of the kinetic energy recovery system — called KERS — that’s used by Formula 1 vehicles. KERS takes the energy from braking, charges it into a battery pack, and then returns it to the cars when they need extra power. The idea behind it was to reduce costs, but going to a smaller engine was a big mistake.
Race cars that don’t sound like race cars aren’t acceptable. If that’s going to be the cost of hybrid vehicles, a lot of NASCAR fans will want to throw up, and rightly so. Our fan base associates stock cars with a throaty V-8 engine, and so do I. That shouldn’t change. If we switch to a four-cylinder or V-6 in NASCAR, we’re going to lose a lot of fans.
But having a KERS system similar to F1 — that can recover energy and use it as needed — is the perfect foundation for the NASCAR V-8 hybrid stock car. The way I envision it, we’d be creating one of the best engines in the world, and it would keep the roar that NASCAR fans love.
https://www.nascar.com/news-media/2018/05/29/brad-keselowski-blog-nascar-hybrid/