[The HACK]

I can answer your question since I tracked my old Z4 3.0i with SMG and my old 350Z extensively.

On paper it's no match. The 350Z should blow the Z4 out of the water. It's got more power, more brakes, LSD, MOAR everything. But in reality the 350Z is more of a grand tourer, with it's 300 HP pulling a 3,400lbs frame, while the Z4 3.0i pumps out a 225hp on a respectable day, it's implementation of brakes, steering, and overall suspension geometry while in bone stock configuration was still much faster and more enjoyable than the 350Z on anything but the biggest HP track out west.

For about 15-18 month I tracked both the Z4 3.0i and the 350Z regularly, the Z4 3.0i I would take to Driving Concept Incorporated events because they allow convertibles, and the 350Z to BMW CCA events because they don't. The 350Z evolved over time with more and more mods, while the Z4 3.0i stayed stock (except for tires).

Power: 350Z for sure. It got me on the slippery slope of needing more hp for the track, since the previous car I tracked was an E46 323Ci with 170HP on a good day. You can ALWAYS use more power. But the way the 350Z delivers power on track is a little disappointing, it does not pull all the way to redline like BMW inline 6es do. It peters out up top, with gobs of torque and pull at the low end of the RPM and then it really tapers off the closer you get to redline. The Z4 3.0i's M54 engine would pull and pull and pull all the way to redline, even though ultimately it didn't pull as hard.

Handling: Z4 by a country mile. Despite both having similar suspension layout, MacStrut up front and multilink rear, and with stock camber settings, the 350Z suffers from lack of caster up front and almost 500 lbs of weight disadvantage. While the Z4 glides around corners effortlessly, the 350Z often gets upset by mid-corner bumps, and struggles with a twitchy frame that often don't quite know what it wants to do. Don't get me wrong, it's quite a performance coupe by most standards, it's just that the Z4 seems to handle going around a corner so much better than the 350Z.

Steering: Another area where the 350Z fell short, despite the mechanical power steering vs. electrical power steering. There's a weird dead spot in the 350Z's steering once you start pushing it hard. I still suspect the chassis didn't have enough caster for what it wants to be, but the harder you drive it, the more vague the steering get, while the Z4, despite all the poor implementations of the electronic boosted power steering, stays relatively consistent no matter your pace.

Brakes: The 350Z fell WAY short here. Again, the 500lbs of extra heft and the 70 or so horses show up here. My 350Z didn't have the track brakes, but at the same time I was tracking the 350Z there were a few friends who track 350Zs with the track package, and they were having the same brake issues I was. The brakes will last about 2 sessions and then get overheated, then they would fade like crazy all of a sudden. I recall going into Buttonwillow's Bus-Stop counterclockwise, with Nissan's top end Nismo track compound, ease into the brakes and realize that they weren't there. Car wasn't slowing down. My passenger at the time, a senior instructor and tent leader, screamed at me to apply the brakes, and all I could tell him was I was literally standing on it as hard as I can. Next session out the brakes gave out at the entrance to Sunset, with no prior warning. I had SO MUCH trouble with the brakes on the 350Z that ultimately what cured it was a $4,000 brake upgrade from RacingBrake. The OE brakes were great for street use, for track use they're useless.

Meanwhile I never even bothered swapping out the brakes on the Z4. Ran OEM brake pads until they needed to be replaced. Sure, they "faded" a few times at Buttonwillow, but they've never all of a sudden disappear like they did on the 350Z. Terrifying.

Chassis: Edge, goes to the 350Z. It's got a fantastically stiff frame with plenty of bracing, and a slightly longer wheelbase if I recall. It goes into corner at speed with little to no flex, and the fixed roof gave some sense of comfort and security in the case of a roll over.

Aftermarket support: Definitely 350Z. Brakes. Suspension. Intake, mainfold, header, exhaust, aero, you name it, someone makes it for the 350Z and makes it CHEAP.

Consumables: Toss up. The 350Z has cheaper consumables (brakes, tires, oil changes) but needs to change more often, so it's a wash.

Ultimately, when the lease was up on the Z4 3.0i, I decided to sell the 350Z and put my name down on an order for a 2006 MZ4 Coupe in March of 2006, knowing that it's the best of both worlds. It's got the lighter chassis of the Z4, more power than the 350Z, but with the buttery smooth ramp-up of the BMW inline 6. It's got the insanely stiff coupe chassis, with BMW handling and excellent brakes stock, and none of that electronic assisted power steering. And at the end of the day I got something that was far above my original expectations, even though my expectations for the MZ4 Coupe was quite high to begin with.