I'm looking into purchasing a FSB for my AP2 but have come across a minor question. I've noticed a few bars out there are hollow like the Eibach and others that are solid like the Saner. I just want to know if I will notice a difference if I got one over the other as far as response.

The car is my DD, does see any track days or autox. Its currently lowered on Espelirs and has a Whiteline Xbrace.

 

There is no easy answer to that. It all depends on the second moment of inertia for each bar in question. I.e. a hollow 23 mm bar may have the same characteristics as a 20 mm solid bar. It all depends on the wall thickness of the hollow bar when comparing to a solid bar. Construction material will obviously make a difference as well...

 

Say for instance I got with the Eibach FSB over the Whiteline FSb, will I be making a wise choice?

The Eibach is 32mm (Hollow) and the Whiteline is 30mm (solid)

 

Both are great quality products, you can't go wrong with either. The only way to notice a difference will be to test them back to back.

 

You'd need more dimensions in order to calculate their roll rates.

You need:
OD
wall thickness
lever arm length to endlink
angle of the lever arm
length of torsional middle section

I think with those dimensions you could come up with an accurate comparison. Check out the methods used in the "characterization of OE springs" thread. TwoHoos goes through how to calculate the roll stiffness of sway bars.

 

^Yes, you'd need all the dimensions to make a true comparison.

However, you can make a rough guess at their relative stiffness if we assume the bars are the same shape. Spring rate goes as 4th power of diameter, and for hollow bars you just subtract the "rate" of the hollow portion. Most hollow bars are btw 4 and 6mm thick, so let's assume 5mm. Then you'd calculate 30^4=8.10e5 for the solid bar; and [32^4 - (32-2*5)^4] = [32^4 - 22^4] = 8.14e5 for the hollow bar.

So without knowing anything else we'd guess these bars are very very close in terms of stiffness.

However, the hollow bar will be much lighter, since the main tube portion has only ~60% of the cross sectional area. [Compare 30^2 to (32^2-22^2)]. That's the advantage of hollow bars: same stiffness with less material (but harder to manufacture).

 

I don't believe it would be all that important unless you track your car quite often.

So as the S2K is your DD you could save some weight and go with the hollow option.

Not that the weight will make any noticable difference in performance anyway.

So long story short, as 06Estukay said, can't go wrong with either.

Go for the one you're drawn to the most. Personally I would go with Cusco. None the less I would trust Eibach knows their stuff just as well.

Good luck