If he's an auto VR6, you should win it. With both cars having 5-speeds, it comes down to more of a driver's race. I ticked off 15.4 with an intake (5-spd). Not wonderful, but not that horrible either.

Jetta VR6's between 99.5-02.5 come with a listed 174 cHP, but that number is misleading. VW under-rates them a bit from the factory, with many stock VR6's dyno'ing near 165 whp and 178 ft-lbs. 3050 lbs is a typical curb weight. The gearing is very tall, 1st - 40mph, 2nd- ~70, 3rd- high 90's.

----------------here's where the guessing begins-------------------

So... as i've said... if he was a 5-speed, he'd pull you off the line, and you'd make up the ground inch by inch on the high end (with good driving). Since he's an auto, you'll probably launch somewhat evenly, and you'll pull him a bit harder at the high end.

The IS300 will give you a much tougher race. Bring your A-game and hope he bogs or otherwise screws up, because you're at a fairly signifigant torque and power disadvantage, as well as RWD. You're likely to get edged out on that one.
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so, there ya'll go.. a semi-comprehensive guide to jettas. Just stay away from a VR6 with boost... most tick off 12's with no problem, and most fairly well-built ones are in the 11's.