I've been researching and interested in installing some underdrive pulleys for the coupe for extra low end power. But as a member pointed out to me, it can become detrimental to the engine, and from my research, they're lighter and bigger, they have less drag, spin slower, therefore reducing the juice to the alternator and pumps etc, but increasing the power it can make. And if it's not balanced right (rotation vs power), it can cause engine damage. What would cause the pulleys to go out of balance? Is this a safe investment? I'm not FI or have any real crazy mods, just 1/2" plenum spacers, K/N drop in with Z tube, and grounding kit. Anyone have any specific and detailed info? I haven't seen or found any threads on this unless I'm blind.

 

You could just get the light weight pulleys not under driven and be safe. I think, as from what I understand, its the weight you want to knock off. I ordered the AMS light weight pulleys and having them installed this coming up weekend. I'll let you know if its worth it or not!

 

I just want to know in what conditions could I put my car in with such an imbalance that it would kill my motor with underdriven light weight pulleys installed.

 

The debate on aftermarket pulleys is that they may screw up the harmonic balancing of the engine, doesn't matter whether they're underdrive or not. Personally, I don't think a few pounds less is going to mess up ****, but I'm not an expert. I've had the UR underdrive pulleys on for about 6 months now and have not had any problems. I haven't dyno'd since so I don't know if they actually did anything or not. My A/C isn't as cold as it used to be, thats the only difference I've noticed.

 

I've ran the AMS light wieghts for hella long now w/ZERO problems. I only avoided under-driven pullies because of all the electronics on the car.

 

i think the problem is that the stock pulley has a balancer on it that the aftermarket pulleys do not. and if the aftermarket pulley becomes off balance. your crank shaft is going to get very wobbly and fudge your shat up.


dont quote me on that. thats just what im thinking i heard

 

AMS 350Z/G35 ALUMINUM RACING PULLEY KIT

- Aircraft Aluminum Construction – ISO 9001 Standards

- Stock Sized Main Pulley (No Under-Drive Related Issues)

- Stock Size maintains OE water pump speed and OE alternator output!

- Fully Balanced

- Metal Sleeve on Main Crank Pulley for a positive seal – no leaking main seal!

- Realize up to 11 Hp and 6 foot pounds of torque

- Power and Torque gains throughout the power-band!

- Total weight of kit is 2.5 lbs vs. 7.6 lbs stock!

- Main Crank Weight is 1.84 Ibs vs. 4.46 lbs stock!

- Anodized Black for an ultimate protective finish!

- AMS Laser Etched Logos

- Includes Crankshaft Pulley, Alternator Pulley, and Idler Pulley

 

Thank goodness I bought those!

 

Good info, thanks guys!

 

so should Dr. G35 have not of put on the crank pulley? just get stock size lighten pulleys and only install two of them, so the stock crank pulley wont ever go out of balance. because the stock crank pulley has like a rubber ring around it witch keeps it in balance and any after market pulley you buy smaller or just lighten wont have it.

have you had any problems with your pulleys yet? how long have you had them on?

 

BTW the post is over 9 months old

Purpose of the harmonic balancer is to absorb some of the shock from internal combustion (IE explosions) that occur at different times and locations on crankshaft. OEM balancer is engineered to the rotating weight and loading of stock engine.

When internal or external engine modifications performed to enhance output this has some affect on engine harmonics.

Aftermarket balancers become necessary to compensate for higher reving/output engines to minimize bearing and crankshaft damage.

By using a lightweight aluminum crankshaft balancer it does not absorb harmonics/vibration correctly which may lead to damage.