eLTwerker

Adding mass to the rotating assembly reduces the available (net) torque when the engine is accelerated. You "lose" the energy required to accelerate the heavier mass. Under steady state conditons, there would be no difference in net torque, except for some minor friction loss for the heavier load on whatever bearings were holding up the mass.

Winding the engine up to 5,000RPM with a very heavy flywheel, then dumping the clutch, would increase the torque at the rear wheels, the answer is yes. The energy stored in the rotating mass would be available to accelerate the car.


The proceeding two paragraphs were written by Injuneer over at cz28.com
Here's my question:What, then are the downsides to a heavier flywheel/more rotational mass? Would the increase in rotational inertia keep the engine at comparably lower rpms to the same engine with a lighter flywheel? In what circumstances would a heavier flywheel(or any added rotational mass, in general) help an engine's performance? Lighter parts would be better in road racing probably, but would the additional available torque help 60ft. times in drag applications possibly at the expense of rpms? Help me understand some basic concepts, please. Thanks!

LiENUS

I was going to post a lengthy explanation here but **** it read the Wikipedia article on flywheels. Because that is what you are doing by increasing the weight

Brief Encounter

iTrader: (6)

That heavier rotating mass is only good for 60Ft. times, after that the lightest possible rotating mass would be optimal. As you spin into the upper rpm's all that extra weight is just eating up horsepower, because the engine is working harder to spin all of that added mass.

1320FEVER

iTrader: (9)

I wouldn't think that heavier rotating mass would affect net torque but it would affect horsepower which is a measure of how fast torque is made. The rear wheels will see the same torque regardless of heavier drivetrain, but it will take more energy to accelerate the mass and therefore reduce the horsepower.

P Mack

iTrader: (6)

The rear wheels would see less torque when the heavier drivetrain is accelerated.

eLTwerker

Would less torque reach the wheels due to more rotational mass to "absorb power"?

P Mack

iTrader: (6)

Yes, but only when the rotational mass is being accelerated. For example driving up a steep hill and maintaining a constant speed, none of the torque would be lost to inertia. In first gear at wot the losses would be greatest.

Rwtq will be affected exactly as much as rwhp because the wheels spin at the same fraction of engine speed, as determined by what gear you're in and your differential ratio.

LiENUS

If you're looking to increase rear wheel torque without touching engine internals you're looking too close to the engine, back up and look at your rear end. A bigger set of gears WILL increase the rear wheel torque and wont cost you any horsepower. And they WILL affect more than just your 60ft times.

XBR24

Newtons 2nd Law

Force = Mass x Acceleration (F=ma)

for a constant force (i.e. not touching engine performance) your mass and acceleration are direct tradeoffs. Reduction of mass (rotating and otherwise) will allow faster acceleration.

When you add a large flywheel you are increasing mass thus decreasing acceleration. Well where does that energy go???? you are storing that rotational energy in the flywheel (potential energy).

Totally depends on what your trying to accomplish.. heavier flywheels make drag racing and street driving easier.. at the sacrifice of acceleration.

Go and drive the Porsche Carerra GT.. it has very little driveline rotational inertia.. my bet is that you will kill it the first 5 launches. It DOESNT sacrifice acceleration for ease of driving.


And as stated above, the mass effects arent a problem when at steady state.. however, the faster you accelerate.. the larger the effect.