The factory power pack is normally only 6.9v. With little effort you can upgrade to a modern AFX power back and make your trucks very responsible evne on the power back low setting of 8v. It has three levels 8v,12v, and 22v. 12v is enough to wreck the trucks and don't even try 22v!
You can find new/used ones on eBay- https://ebay.us/3gORGr and sometimes on Amazon- https://amzn.to/3AT1jbs
You can find new/used ones on eBay- https://ebay.us/3gORGr and sometimes on Amazon- https://amzn.to/3AT1jbs