How many owners have noticed engine vibration (around 2500 rpms)?

[RamAirZ]

Well alot of it has to do with packaging, parts interchangeability, a certain goal they are trying to reach etc., and like with 4 cylinders, sometime it's just something you have to do. The 4.3's didn't start off with a balance shaft but they ended up going to one to try and smooth out vibrations. All crankshafts have counterweights but sometimes the design of the engine and the firing sequence can produce unwanted vibrations. Take the 4.3 for example, it's basically a 350 chevy with 2 cylinders chopped off. But due to the firing sequence, it's a shaker! In a V8 it works fine but in the V6 it makes it lopey. Here's a good read:

http://en.wikipedia.org/wiki/Balance_shaft

[89Vette]

Here's a good read:

http://en.wikipedia.org/wiki/Balance_shaft

Thanks. I note this paragraph at the end of the link....

"Another balance shaft design is found in many V6 engines. While an inherently balanced V6 engine would have either 60 or 120 degrees angle between the two banks of cylinders, many current V6 engines are derived from older V8 engines, which have a 90 degree angle between the two banks of cylinders. While this provides for an evenly spaced firing order in an 8 cylinder engine, in a six cylinder engine this results in a loping rhythm, where during each rotation of the crankshaft three cylinders fire at 90 degree intervals, followed by a gap of 90 degrees with no power pulse. This can be eliminated by using a more complex, and expensive, crankshaft which alters the relationship between the cylinders in the two banks to give an effective 60 degree difference, but recently many manufacturers have found it more economical to adapt the balance shaft concept, using a single shaft with counterweights spaced so as to provide a vibration which cancels out the shake inherent in the 90 degree V6."

The last couple of sentences seem to explain why some engines have a balance shaft and why the VX does not. I just noticed this evening that the 3.5L crankshaft sells for over $1000!

Since I doubt this is an availability thing (because the 3.5L was in other vehicles), I would appear a more expensive crank -- referred to in Wikipedia -- has been utilized in the VX. IOW, it doesn't have a balance shaft because it doesn't need one.