TwinTurbo.NET: Nissan 300ZX forum - Underdrive pulley VS. Stock harmonic balancer
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Subject Underdrive pulley VS. Stock harmonic balancer
     
Posted by HakenTT on November 12, 2004 at 7:50 PM
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Message I would like to get into discussion on underdrive pulleys vs. stock harmonic damper/balancer as I searched and did not find any post that explains the both parts in depth. I did some research and found out that for us bog power adders the stock pulley will be better as it will help save rod and main bearings. As for stage 3 TT it would probably be OK.

To my sorprise NA and TT pulleys are the same exept TT has bigger ring on the outside of the pulley and 4 grooves for PS belt. Its obvious that Nissan engeeners did this for reason. TT ring is bigger because TT produces bigger power which brings more crank twist, the bigger ring helps eliminate bigger twist.

Torsional vibration is a twisting vibration caused by the pulses of each combustion event. The force of the piston causes the crank to deflect ever so slightly in the direction of the force, and when that force goes away the crank ever-so-slightly springs back. At certain frequencies the crank can resonate, making the vibration much worse. This is where the harmonic dampener comes into play.

The other benefit of aftermarket pulleys is to reduce rotating mass. Here the simple aluminum crank pulley has a big advantage over the heavy stock pulley, but there's a reason it's so much lighter: It's missing the harmonic dampener. The reduction in rotating mass may be worth a couple of horsepower. But removing the dampener seems like a bad idea to us.


from internet:
On a race motor, increased risk of bearing or crank problems is insignficant next to the risk of, say, detonation in the cylinder that could blow up the motor. So for a race block, we heartily endorse lightweight undampened crank pulleys.

[[ http://www.machv.com/tip11cranpul.html ]]

As for underdrive pulley as seen here:

[[ http://www.specialtyz.com/udpulley.htm ]]

The pulley does not dampen the crankshaft at all reducing the life of the engine bearings.

Although many Z32 owners have removed the harmonic dampener crank pulley without incident, doing so almost certainly increases crank bearing wear, and COULD lead to early failure of the crank or crank bearings. Just how much the life of these parts is shortened is unknown.

From specialtyz:
"These high quality pulleys offer a significant power increase for both Non-Turbo & Turbo. Not only do they spin the accessories slower for more power, but they also weigh less. Taking weight off the crank frees up more horsepower."

Does anyone agree?

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