bpc576

so im curious to hear what you guys on here think about light weight crank pulleys. i dont have a civic anymore but i have a 2.0 turbo volvo and nobody seems to be able to give me a straight answer about if they are potentially bad for the motor. i figured the honda guys i remember talking to when i had my civic seemed to know way more than the euro guys. anything you guys can advise would be great! thanks so much!!! oh and its not underdrive. its oem size just 75 percent lighter

mac25

Well it depends on your crankshaft setup.

The theory goes (I have not tested it) that the Crankshaft pulley on civics doubles as a harmonic balancer, and that,

a harmonic balancer adds another material to the crankshaft unit which removes the potential for the crankshaft to vibrate at a frequency which would damage the crank or other engine components.

But It's hard to tell what is truth and what is net folklore on issues like this where people are too afraid to actually test the outcome.

I myself was going to run a set of lightweight pulleys with my lightweight flywheel, until a friend into subarus said that it was a bad idea.

Honestly I do not know if this is a real issue or if manufactures/net heros advise against it in theory only.

bpc576

What im thinking is that the controversy has to do a lot with engine setup. i can see how a lightened and non dampened pulley could affect a motor with multiple plains on which force travels, like a V engine or a boxer engine. but an inline 4 only has force from one direction. not to mention that on the other end its connected to a very heavy automatic transmission full of heavy spinning parts in my case. if someone wanted to put a lightened pulley on a big v8 i dont know if i would advise it. but on a smaller hp car with an inline motor and a big flywheel im not sure how much dampening it really does. im sure there is a lot more vibrations in those subaru boxer engines. just like how a harley vibrates way more than a sport bike.

ezone

The harmonic balancer is a torsional vibration damper, and on some engine designs it can be a location for external crank balance weights.

It dampens the twisting forces and inherent flexing ("torsional distortion") of the crankshaft between individual firing events.

Not only is the multiple piece design important, mass (weight) is also important.

Without it the damper function, the worst that could happen is........the crankshaft could fracture and break.

Will that happen? How long would it last without the damper function? I can't answer that. I wouldn't do it though.


Google for more, because the more you know:

https://en.wikipedia.org/wiki/Harmonic_balancer

http://www.agcoauto.com/content/news/p2_articleid/273

Vertigopills

Unorthodox racing makes lightweight power steering and alternator pulleys at stock diameter... I was thinking of getting those at some point for my stock 97 EX. Thoughts? They claim 1-2hp gain for each mod. I realize that spending almost $300 for 2-4hp is madness, but I'd be okay with just the fact that it reduces the rotational mass and therefore stress on the engine. They also look good, hard to argue with that haha.

ezone

If you want to spend that kind of money for looks, go for it.



Don't bother if you re looking for performance. A claim is just a claim, "up to 2-4 hp gain" includes zero.
You could instead leave your spare tire and jack at home and make an actual gain in power-to-weight ratio.

Stress on the engine? No.
Have you actually felt how light the stock pulleys are?
The rotating assembly (crank, rods, flywheel, clutch, etc.) probably weigh 70-90 pounds already, a few ounces difference in the accessory pulleys is negligible.



/rain on the parade