It doesn't effect the warranty(according to my service manager at my dealership). All it is doing is to increase the grounding of the vehicle from the standard 8 gauge with galvanized ends, to a 4 gauge with gold plated ends. The theory is that the larger 4 gauge & gold plated ends will conduct the current more efficiently & give you a more consistent ground for the extensive electronics that are in these cars now days. This is very similar to building a stereo system in a vehicle or boat & using the larger power cables along with gold plated ends.
As I said in my original post, you'll get some debate from people on the boards here as to a tangible benefit from this, but I can tell you a measured benefit I've seen is the lowering of the neutral idle from 800 RPM's to about 500 RPM's after installing it. The idle also smoothed out a bit. I used to experience a slightly rough idle (usually when we had drastic weather changes in TN) occasionally, until the car was run for a little while. Now, I always get a consistent idle. I think the shifting in manual mode (I have the auto stick) is slightly crisper than before, but that may be just my perception.

One last thing regarding the Z4. I was out driving Friday night & a young guy driving one decided to 'play'. I can't say how the performance stacked up from a dead stop, but he decided to 'punch it' from about 40 MPH. He even jumped before me & I caught & passed him quickly (in normal automatic mode). He did it a second time from about 30 MPH, & my Z opened up an even bigger lead on him in manual mode. Now, this was highway straight line stuff, no curves or dead stop stuff, and the Z really 'put it on' him. He pulled up afterwards, shook his head, pointed to the Z & gave a thumbs up!
You can't go wrong with either vehicle. Both are great engineering. Performance is probably pretty similar (although I'm a bit biased towards the Z!), but I feel the styling on the Z is something that stands out better. I bought this car for many reasons, not the least of which is to get noticed. The Z Roadster is more limited production & gets a bunch of attention.
Unfortunately, the Z4 has gotten a bit of a reputation as a 'woman's car' (not my words!), because you seem to see a lot of women driving them. Mostly because when they came out (Z3), women bought them "because they're just so cute"(!), and they were very affordable. Sometimes it's hard for a car to shake stigma's attached to them.
Good luck with your decision, you won't go wrong with either one!

 

[QUOTE\
Well, I got some thinking to do. My gut tells me I want the BMW, but the Z is damn close and a lot less $$. Thanks for you help! [/QUOTE]


Let us know what you decide. Either way, you can't really go wrong.

 

The real question is do you go for the bling bling or the sports car?
For me it's simple, I've diven the Posche Boxter, the S2000, BWM Z3, the Benz SLK, and the Z Roadster. To me there are only two real sports cars in that group. The Z Roadster and the S2000. I choose the Z Roadster because it has more useable power during normal driving and I'm 6'3 and don't fit well into the S2000. As far as the the rest. The BWM 3.0 L is not even remotely powerfull enough to compete with the Z car. The SLK is a joke. And the Boxter was disapointing in power and exhaust note. So the real question you need to ask yourself is, do I want a sports car or yupie mobile? The only German car that compete with the Z is the Boxter S, but be prepared to pay double the Z price for it. So if you are still undecided I have a suggestion, go look at some SAAB's, there good cars too.