strut bars?

Yesterday I drove my friend's new 350Z and it was fast and cool but, there was something weird in it. I haven't driven a sport car before except a 2001 Impreza and it was a bit faster than the 350Z because the Z I drove was Auto, not a stick. Anyway.. When I drove the Impreza I didn't feel what I felt while driving the Z. The Z was hard on the ground, it kept jumping and shaking (vibration) at the front and I had a weird, but great, feeling while taking curves and corners. After we got back I told my friend to open the hood and there it was! A Strut bar!

Now, What I want to know is..
-- What's the main reason of strut bars?
-- Do strut bars affect on engines performance? If yes, how?
-- Why does the car seemed to be shaking/vibrating while accelerating? Is it because of the strut bar?
How to deal with this shaking/vibrating if it was because of the strut bar?
-- Would it be better to have a car with or without a strut bar?

That's all I want to know..

Thanks.

strut bars (or sway bars) are used to keep body roll to a minium. to sumiluate body roll go in a geo (or similar small car) and go around a clover leaf ten mph faster then you think is normal the abnormal tilt you get is body roll (you could also put two varry fat people on one side of a car)swat bars help becouse it stiffens up the frame consideribaly
(an example of what it does can be seen if you take a model runner ie plastic little car and and twist it and push it on the sides if its just a rectangle it will flex and bend but if its got runners going lenthwise it wont flex so much)
clif notes version: viagria for the frame

pod - you're confusing a sway bar (aka antiroll bar) and a strut bar.

A strut bar connects the tops of the strut towers in a Mcpherson-type suspension (or derivatives of one) and thus stiffens the frame. Basically, the way it works can be explained by the fact that a
______
|____| construction is stiffer than a

|____| construction. The top element of the first diagram represents the strut bar. The strut towers are the side elements. You'd be amazed at how much the latter can move in relation to the rest of the car.

Here's one installed in a car

http://www.fourthrock.com/maxima/images/front_strut_bar.jpg

An example of a sway bar can be seen here (http://4g64.150m.com/full%20sway%20bar%20view.jpg). It stiffens the suspension and prevents body roll, but does little to stiffen the chassis itself.

Well I've seen it already on the 350Z but what I am wondering about is, does it affect on the engine's performance? Would it be better to have one on the car or not?

How would it affect the engine? It's just a metal bar that connects the suspension mounting points. It does affect handling though. Improves grip and maximises rigidity. Front one is likely to increase understeer (on a fwd car), while the rear stb switches the balance towards oversteer.

the car was bumpy because it has a tighter suspension than the imprezza. Strut tower braces or (strut bars) are one of many ways of stiffening a chassis. the 350Z is overall a much stiffer car due to it's design (coupe vs. sedan, etc) that is not the say the subaru has poor handling, it is simply not as stiff. Sway bars, or anti roll bars are different.
strut tower braces are a good way of making your car stiffer and have tighter, crisper handling.

the car was bumpy because it has a tighter suspension than the imprezza. Strut tower braces or (strut bars) are one of many ways of stiffening a chassis. the 350Z is overall a much stiffer car due to it's design (coupe vs. sedan, etc) that is not the say the subaru has poor handling, it is simply not as stiff. Sway bars, or anti roll bars are different.
strut tower braces are a good way of making your car stiffer and have tighter, crisper handling.
It's quite impossible to mention which car has the stiffest chassi based on if it's a sedan or coupe, for example Saab 9-3 Sport Sedan has a higher chassi stiffness than Porsche 911, Viper GTS-R with roll cage, Lamborghini Murcielago or Corvette Z06. The stiffnes can also often be increased alot with simple means, a little more than a strut bar though.

It's mostly likely that the impreza and a 350Z has a different suspension, the impreza having a more soft forgiving suspension than the 350Z.