It's funny you think there might be some reasonable plot mechanism. I watched part 7 the other night and there's a scene where Vin Diesel gets out of his car with a shotgun facing the main villain and he's like "what? you thought this was gonna be a street fight?" Then he throws the gun in the car and grabs giant wrenches and says "YOU'RE GOD DAMN RIGHT IT IS" lololol

Then Jason Statham the villan just casually reaches under the hood of his car and pulls out 2 long jagged pieces of metal the exact size and durability of Vin's wrenches and they go at it. Vin does get hit in the face with the wrenches a few times but he shrugs it off like its no big deal. Then he proceeds to throw Jason Statham 15-20 feet like a rag doll multiple times.

At some point a helicopter shows up and tries to blow up Vin with a rocket... but it just destabilizes the parking garage they are fight on. So Vin says "THATS THE THING ABOUT A STREET FIGHT. THE STREET ALWAYS WINS!" So he slams his foot down causing the ground to collapse under Statham and get pinned under a huge concrete slab. Eventually the structure is completely destroyed but we discover he's fine later on when he's in jail.

The helicopter of course keeps shooting at Vin, but it's ok because the Rock had a broken arm and just flexed out of the cast and broke it which meant it was fully healed. Then he wrecked an ambulance into a drone going 125 miles per hour in mid air, stole the gatlin gun off of it and shot the helicopter with it. Of course it wasn't quite enough to knock down the helicopter so Vin had to jump his charger off a ramp, do a barrel roll and hook a bag of grenades onto the chopper. The rock shoots the grenade and blows up the chopper and all the baddies are dead.

Of course after jumping a car off a ramp on top of a building Vin Diesel is dead. Paul Walker tries to give him CPR but that pisses off Vin Diesel's girlfriend and she's like "get the fuck off him stupid." So she says some bullshit about this one time in Mexico when we boned and he's like "oh yea, i'm alive"

The End.

So... really it doesn't matter what the plot is. There will be fast cars, explosions and at least one party scene where they zoom in on bitches' asses.