A jet engine. The fastest car I've ever been in was a 911 Turbo, I was a passenger in the car going down 495 doing 175, it was silky smooth and all you could hear was a high pitched keening sound. There was more left too, but the highway started to turn too much.
I've raced a 911 Turbo twice and beat him twice. What you will need is about 450 HP to the wheels. Heads, cam, intake, exhaust and a power adder (supercharger, turbo or nitrous). Oh and shut down early against the 911. They really shine from 125+ MPH.
Fastest car I've ever ridden in. My bud has some kind of stage 3 kit on his 911 turbo. He claims 10's, which I believe cause it's faster than our shops old race car (turbo rabbit) which ran 11.02. This was a VERY sivilized car. I actually thought I was gonna die in it cause he was doing 130 down the street in no time...it was 4wd too and you could feel it kind of floating from the spinning. Scared the bajesus out of me.
It needs the "Saleen S7" mod, or the "Ford GT" mod. All you have to do is replace the whole car with either of those, and you'll beat those pansy a$$ 911's all day.
There was an 03 cobra in the MM&FF that would prob do it. Stock long block, whipple s/c and all the bolt ons. Guy was putting down like 600 somehting to the wheels if I rem correctly. That should take care of any of those pesky foreign super cars.
911 Turbos are usually full of other high end stuff besides just a lot of power: brakes, suspension, steering, ect. Try 4 or 6 piston brakes, literally a race prepped suspension, and 4wd that will take you wherever you point the car.
A new stock Viper would be close. A new 911 Turbo can easily run upwards of $175,000 (w/typical costly options). I believe the new car puts out 450hp roughly, probably a bit more in reality. Just looked up the price at Edmunds.com and OMG, the options list is very long and expensive. I bet you could rack up more $$$ in options than the price of a new Cobra.
I'd think 500hp and major suspension mods should give you an edge, plus a very reliable tune. Of course, the better driver you are compared to the 911 driver helps a lot also. As stated, stay away from high speeds, as cars like the 911 were made to be extremely stable at anything short of top speed. Definitely would be an interesting situation.
I don't know alot about those cars, but didtn' they come w/around 450hp??, if you want to run in the 1/4, h/c/i w/power adder and enough suspension to get you to hook, i think that would be close, around a road course, a lot of cathing up to do. just my opionon, could be wrong.