Older cars, despite the big numbers they may pull on the dyno, tend to be slower than today's cars. So, the Haldex AWD car my pick for the faster accelerating car.
An early 2000's Pontiac Bonneville SSEi with the L67 motor, gets the 0-60 in 7.7 seconds. That's bordering on slow by today's standards.
A stock TourX AWD already does the deed in 6.3 seconds.
I shouldn't have made it so easy by mentioning FWD, but most guessed correctly. The mystery car in question is a 2000 Bonneville SSEi w/ L67 3.8L.
The Bonneville was a normal L67 with these mods when I had it dyno tuned: 1.9 ratio rocker arms, 3.3" pulley, E-bay stainless tube headers, high flow cat with Flowmaster super 44 mufflers (OEM exhaust otherwise). When they were dyno tuning it, they determined my knock retard (which I knew was excessive from my own scanning) was from a faulty fuel pump and replaced it with a Walbro high flow unit. Total cost of mods, I'd be surprised if it surpassed $1K.
The Buick is seriously handicapped by some electronic wizardry which I'm convinced limits torque in the first couple gears, even with the Trifecta tune. As such, it can't really take advantage of AWD in a 0-60 or stoplight race. Despite the Bonneville being seriously traction handicapped where it would roast tires well into 2nd gear (if you weren't careful), it sure felt a LOT faster from a stop. Even from a 20-70mph roll, I don't think the Buick could keep up.
(Bonneville video:
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These two cars have comparable weight, wheel horsepower (if you trust the Trifecta tune dyno graph)-- the differing factor is that torque comes at wildly different places between the two. But given the advertised power specs with the Trifecta tune on my current car, I can't help but be disappointed in its off the line performance, especially given it has an 8-speed which should keep it in the prime powerband (where torque is less important) once you hit 10-15mph or so. Rather, it spins up to 6K RPM or so in the first couple gears like it's a N/A car. Don't take this as complaining, I didn't buy a racecar nor did I want one, but I believe published hp/tq specs on newer cars are likely valid only under certain conditions because of all the computer control.
All that said, mash the throttle at 45mph and the Buick is a whole different animal (especially with the tune) and I'm convinced it would dust the Pontiac hands down at higher speeds. 100mph+ comes in a hurry and it drives better than the Pontiac ever could.