Old Cartoon Network anime, rival has a spaceship slightly better than the protagonist's and they know how many more hits it takes to destroy a ship

I think the show you are describing is SWAT Kats: The Radical Squadron.

Using discarded military parts and weapons from the salvage yard, Jake and Chance built themselves a three-engine jet fighter called the Turbokat, which resembled several different jet fighters, most notably the Grumman F-14 and the Saab Draken, along with a handful of other vehicles such as the Cyclotron (a motorcycle built into the jet's seating, deployed from the bomb bay of the Turbokat like a missile), the TurboMole (a subterranean vehicle used to drill underground), the HoverKat (a militarized hovercraft), and the Thunder Truck (a militarized Jeep modified from their tow truck). All these vehicles were stored, along with a training area and other equipment, in a secret hangar below the yard. Razor and T-Bone now patrol Megakat City as the SWAT Kats, defending it against any kind of menace that threatens the city. Their enemies include the criminal mastermind Dark Kat, the undead sorcerer Pastmaster, the mutant evil genius Doctor Viper, and the robotic gangsters the Metallikats. The SWAT Kats also face many villains-of-the-week, such as Madkat and Volcanus.