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n2daizo123 -> RE: balance shaft (4/18/2006 8:22:15 AM)
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I got this from nissan performance mag:
Inline four engines tend to be naturally imbalanced. They tend to vertically shake when the cylinders go through their firing order. Increasing the displacement of an inline four (bore and/or stroke), tends to make a four banger's vibrations extremely annoying. The QR25DE is blessed (some would say cursed) with a 100 mm stroke, one of the longest seen on an inline four currently in production. To eliminate the vibrations that such a long stroke would cause, Nissan added a set of balancer shafts to the QR engine. Balancer shafts are counterweights that spin at twice the engine speed to give a smooth feeling to the engine. Usually balancer shafts are integral to an engine design. i.e., hard to remove. Nissan, however, chose to place the balancer shafts in the oil pan, right where we can get our grubby little hands on them.
But why would we want to remove the balancer shafts in the first place? First, balancer shafts spin at twice the engine speeds; at 6,000 rpm, the balancer shafts are spinning at 12,000 rpm. At such a high rpm balancer shafts have a tendency to seize, something you do not want to happen to your performance car. Second, balancer shafts are operated via a short chain by the crank shaft so they basically consume some power from your engine. Removing the shafts should reduce power loss and divert it to the wheels. The power gained from balancer shafts removal (BSR) is not clear. Some have claimed a 7-8 hp increase.
Between 3,500 and 5,000 rpm there is an intense vibration/resonance on accelerating and engine braking. This has been reported by many Spec V owners who have done the BSR and have installed motor mount inserts. Most Spec V owners tend to get used to it after a while.
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