absolutely, the point is to reduce the weight as much as structurally sound. I'd like to see a pic of an HHR-SS crankshaft pulley just for verification that it indeed has the pwr str. pulley negated.

Ours weight half the weight of the stock one. I'll post exact numbers.

 

Stock crank 64 oz
My crank 23 oz
Stock alternator 6.4 oz
My alternator 3.0 oz

 

So now that I have read this forum what was the final outcome? I'm game to try the pulley on my HHR/SS i should be dynoing it Thurs. the 13th of March i can do a before dyno pull and a after. Send me the pulley

 

A pully that doesn't change the drive ratio can't effect HP unless you measure it on an inertia dyno and neglect to take the weight into consideration. I always found it amusing when people put aluminium or carbon fiber drive shafts on their F-Body and claimed it gave them 10 HP. It might have made them faster at the drags due to the decreased rotational mass, but more HP or torque, not a chance. It's the flawed testing the high performace industry does. Bring it to Oxnard and I'll put it on our eddy current dyno at a constant RPM and we'll see what it really does to the engines power.

Ira

 

At a constant load and RPM, yes there will be little power gain, but just the less rotational mass will free up a few horsepower.

But on a dyno while accelerating you will see the added benefit of the lighted material. The lighter rotational mass can and will help with acceleration, and you will see a gain in HP will accelerating across the whole RPM range.

 

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.

 

It should be noted that reducing mass at the pulley also effects crankshaft vibration damping. Crank harmonics shift all over the place. The small HP gain that only will appear during acceleration must be considered against possibly decreased crankshaft and main bearing life.

 

You are making the engine more efficent. You going to tell me that it takes the same amount of work to lift a 5lb weight and a 10lb weight. It requires LESS WORK TO lift the 5lb weight, than the 10lb weight.
YOUR DOING THE SAME ACTION...Period.
Lighter pulleys should make you slower...are you serious. Your making the engine more efficent. How that is slowing you down is FAR beyond me. You must have never put lighter wheels on a drag car. "IT GOES FASTER, not slower, in the 1/4 mile."

Tell all those people with lightweight flywheels they wasted their money. Tell all the pulley distributors, and lightweight clutch and flywheel manufactures that their products are crap, and slow you down in the 1/4 mile. Call one. They will laugh in your face if you told them that.

All ecotecs have internal balance shafts. I'm sure you never seen how "out of balance" a stock crank pulley is, and how "close to 100% balanced" a CNC machined billet aluminum pulley is. You could always balance it if your that anal about it, but there is no need since MOST CNC pulleys are far better balanced than stock pulleys. Hell they even have less run out than the stock pulleys.

 

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

 

Now your talking...