There's an interesting debate going on at a MB forum where a vendor is offering for sale a stock diameter but light weight crank pulley.
He's claiming >10HP power gain across the rev range and at least 3mpg gas improvement.

I'm sound on my physics and the benefits of such a device, but I'd be interested in comments from tuners and others on this forum who have looked into this.

FYI

I can understand how it would enable the engine to rev faster to red line (if only marginally) thus hitting peak power faster much like a light weight flywheel - but I doubt adding 10HP and 3mpg which can actually be measured on a dyno / on the road ???

 

3 mpg, 10 Hp and rev faster by adding a pulley? That sounds a little optimistic to me. The hp can be measured, but the mpg has way too many variables to quantify.

 

A LWF does not add any power or reduce the torque; it only makes the engine revs up faster during acceleration.

 

And offers quite a noticeable difference in acceleration... quite noticeable indeed

 

I'm clear on the flywheel, what about the pulley?

 

as calculated for the crank pulley in question.

Doesn't add any peak power of course and the gains under the curve are determined by the rate of change of RPM which in our cars in the lower gears can be really quite fast :-)

Hence the extra umph from a lightened flywheel in the lower gears.

I just don't buy the 15HP plus / 3mpg gains from just a pulley on a modestly powerful MB sedan.

Heck I'm getting the 'TT mod itch' again.....

 

all of it has to do with inertia...Assume that all moving parts of engine idling weights 50kg.now you want to accelerate...50kg have inertia that tends to avoid your will to accelerate...because you try to make them rotate faster...If you had 40kg their inertia would be less so the engine would raise rpm faster...this rule applies to all rotational moving parts whether it is flywheel,pulley,rods,crankshaft or even wheels...However of course it does not add any horsepower.The benefit depends upon the weight difference.On the other hand when an engine leaves the factory it is extremely well balanced to rotates at specified rpm...By reducing rotational mass on the end of the crankshaft(where the pulley or the flywheel is bolted)we unbalance the whole system...The best way is to get the desired flywheel,pulley,pistons,rods and every other rotated item and balance them together with crankshaft before assemble the engine...