I've been looking to continue to add bolt-ons that add more power and got curious about lightweight pulleys and underdrive pulleys. I found this review and wondered if changing pulleys and belts can really add 6-9 HP?

Read the article and let me know what you think, especially if you have changed yours out. This was pulled from:
http://www.turbomagazine.com/tech/04...set/index.html



"Unorthodox Racing, Inc., which has been researching and developing lightweight underdrive pulleys since 1995, found huge benefits with lightweight pulleys. In-house testing revealed 85 percent of performance gains came from reduced weight and 15 percent came from underdriving. So Unorthodox Racing concentrates on manufacturing lightweight pulleys instead of just underdriving the pulleys.

Most of the Unorthodox Racing pulleys feature only a 15- to 20-percent underdrive. All Unorthodox pulleys are constructed from billet aluminum, which are then machined on computer-operated CNC machines to .001-inch tolerances.

For our testing, we chose a 2003 Nissan 350Z track model equipped with an Invidia exhaust, AEM intake and Sun Automobile Hyper Ground System. The 350Z baselined at 238.8 rear whp on the Dynojet chassis dyno. Installation of the pulleys requires new alternator and air-conditioning belts due to the smaller diameter crankshaft pulley. It's a direct R&R affair.

The Unorthodox crank pulley is only 1 pound 5.2 ounces, compared to the stocker's 6 pounds 3.2 ounces. The Unorthodox alternator pulley is 3.0 ounces, while the stock measured 6.8 ounces. And the water pump pulley came in at 7.6 ounces vs. the stock of 14.0 ounces. That's a total weight savings of 5 pounds 8.2 ounces. On the dyno, the reduced weight, along with the pulley's 15 percent underdrive design, resulted in a gain of 6.1 peak hp as Peak output checked in at 244.9 hp. At 5500 rpm, we witnessed a gain of 9 hp.

The increase in output was noticed in quicker revs and a stronger pull to redline. At $399 for the pulleys and $35 for a new drivebelt, the Unorthodox pulleys are a must-do performance modification. Lighter is better."

 

Probably get that with a tune, lots of guys on here are running unorthodox pulleys and what not I am sure they can give you some kind of idea.

 

Unorthodox is a recognized company and they have the dyno results to prove these lightened pulleys work to make HP. The $434 isn't cheap but we've all spent more for less results! Right....well I have! Intake manufactures make claims of more HP gains than this and we all know this isn't always true, sounds good.
Gary

 

I've read something about these HP increases being seen at the crank but somehow not translating into anything substantial at the wheel. IIRC it was something about the stock pulleys being dampened and the Unorthodox pulleys being undampened, and more about harmonic balancing. There are several threads on here that talk about this.

Here we go: https://g35driver.com/forums/2664818-post7.html

 

Pullies make a huge difference because they are much lighter then the stock pullies in our cars. The lighter weight allows them to speed up faster and easier giving you more power and less weight. The $450 is absolutely worth it.

I'm surprised more people on here don't get pullies as one of their first mods.

 

You should do some more reading on the subject. If it was just weight that made the difference, then everybody would have them. But it's alot more complicated than that. The post I linked to is a very good summary, but it's just a summary, you should read more on them before you decide to buy them.

 

UDP used to be the most highly debated mod hands down... there was a time when a thread like this would go for dozens and dozens of pages... it seems these days no one debates it anymore - they save it for the TBS!

 

I thaught pullies doesnt give any gains, instead they just give us some of the hp that lost during the process of power getting to the ground. Meaning its just releasing some power the engine already had.

 

I've run pulleys on cars before and had problems (partially due to shoddy installation). The only drawback directly from the pulleys was the underrunning of the alternator. If you've got a stereo system with a large current draw you will either die out on the road at some point or have to ride more often with no stereo at all. Also make sure a reliable mechanic does the work if you don't do it yourself, I had one pulley weld itself onto the alternator years ago when the gap wasn't correct (AEM Pulley)

 

There are definitely cars out there that can benefit greatly from underdriven pulleys, but the G35 isn't one of them.

 

I've had good luck with pullies on other cars. I've actually even made Aluminum pullies for my current car. Before you call it ghetto, i have access to a full blown CNC lathe. I draw up the pullies in CAD and programmed the machine and made them. Cost me $50 in material There are downsides you need to prepare for. You need to realize that your water pump and alternator and A/C are now spinning slower. You can conpensate with overdrive alternator pullies, capacitors, more efficient cooling system with larger radiators, aftermarket alternators that make more power at lower RPMs, etc. All that, to gain 10HP at the flywheel...and maybe 3HP at the wheels.

So at idle in traffic, your car may run hotter, your battery may start to drain, and your a/c won't be as warm as it could be. Might not be a good idea if your car is your office commuter vehicle in South Texas heat.


And ~$450 for UDP's!!! Holy crap those are the most expensive pullies i've ever seen! Needless to say, i will not be putting them on my G35

 

What if you just got lightened pulleys that are the same diameter as stock? Obviously less power gain but I gather the purpose of pulleys are to get through your power band faster to achieve the more power more quickly therefore making your car faster than the other guys or girls. Its not about peak power. Its about who makes the more power faster

 

You need to think about the entire rotating assembly of the engine though. The pullies are connected to the crankshaft, the connecting rods, the pistons, the flywheel/flexplate, the torque converter, the timing chains, the cams, the lifters, the valves, and then you have the friction of everything internal as well.

All of those are made of a denser heavier steel. Changing the pullies to AL does reduce this mass somewhat, but it's probably a 1-3% reduction in reciprocating mass....if that. Most of the gains made by pullies are in fact caused by slowing down the serpentine belt system requiring less HP draw to the accessories.

 

And don't forget they aren't dampened. This is not a minor issue. As DaveB said in the link I posted, and in several other places I've read, the lack of dampening can cause unwanted vibrations through the crankshaft which is not good for the engine or for generating power. Like I said, if these were such a great mod, then many people here would already have them!

 

Many of our members do have these types of pullys. Not having a dampner on our engines will shorten their life, that's not something I'm willing
to do....
Gary