Originally Posted by nerraD

An important point about the stock pulley...
It has a center section (hub) that is isolated from the pulley itself, using an elastomeric damper. The elastometric damper is used to partially isolate any nasty resonance effects that may otherwise become apparent from directly coupling the accessories to the crank with a single piece pulley design.

Although the CNC machined aluminum pulley itself will very likely be better balanced, the loss of the elastomeric damper will result in other undesirable vibrational characteristics to become apparent. For most people interested in improved performance... they may not care about this.


As far as the horsepower debate goes... I think everyone is stuck on what constitutes the "engine" and what constitutes the accessories, drivetrain, other loads on the engine... etc.

From a thermodynamics standpoint, the engine will not make more power. However, reducing one of the loads on the engine will allow for more of the power (that the engine already makes) to be made available to the wheels.

I don't think anyone doubts that the lighter pulley will make an improvement to the available power to the wheels. This is no different than removing an accessory load altogether... like a power steering pump for example or an a/c compressor.

The only real question is how much of a noticeable difference it will make. That's the question that we'll keep debating until someone gets some real numbers to back it up

Originally Posted by -md- HHR

~~Claps~~
In my personal opinion you do not need the elastic ring. The ecotec has internal balance shafts, and the small bit of vibration caused by a billet pulley can not be even noticed. poly engine mounts will cause 1000% times the vibrations that the crank might make.

Originally Posted by mistermike

The elastomer isn't a question of balance, either static or dynamic. It's the method of damping torsional resonant modes in the crankshafts themselves. There are scores of internally balanced crankshafts, but you will almost never see a production engine without a damper. Virtually every NHRA and NASCAR team out there uses ATI elastomeric dampers on their engines. These things cost several hundred dollars, and ATI doesn't give them out for free. Some crankshaft manufacturers will not even warranty their products if the dampers used are not on their approved list. The effect of these dampers isn't subjective. It's well studied and understood phenomenon that's been part of every engine designers training for the last 50 years, and unchecked torsional modes can wipe out main bearings and crankshafts in short order.

Originally Posted by nerraD

-md-HHR
Do you have a link to a picture of the GM Perf Parts pulley, for the L61/LE5? Would be neat to see what it looks like.

Originally Posted by -md- HHR

I agree it is not a question of balance. The stock cranks balance SUCKS. Ecotecs are not spinning at 9-10,000 RPM's like Nascar motors do.
Also, GM Performance Ecotec Billet L61/LE5 Crankshaft Pulley p/n 88958631 does not include any elastomer...vibration damping ring.

Originally Posted by nerraD

I can't remember if the stock Solstice/Sky LNF has a pulley with the elastomeric ring... I will have to check tomorrow.

Originally Posted by lazaino

Horsepower is a measure of work, changing the pulley has no effect on the output of the engine, it may allow the work to be used more efficently or it may chage the feel of that work, but it doesn't change the HP of the engine.

And FWIW, the ony real way to get an accurate HP number on a typical automotive dyno is at a steady RPM, otherwise it's up to the software how it figures the inertia in it's calculation of the current torque output.

And for those only interested in drag racing, if you have traction, a lighter pulley should make you slower, if you don't have traction a lighter pulley will make you faster. Same as changing the flywheel weight. In a drag race heavier is better, on a road coarse, lighter is better.