Quote:
Originally Posted by elsolo
powerglides don't run a flywheel, they use a flexplate
Pro-stock doesn't run automatics anyhow, they have a clutch and flywheel
Reducing the rotating mass in an automatic is important, but they do it with aluminum drum, which has even less difference because the diameter is so small.
If heavy flywheels are so great, why does everybody run a 7.25" or smaller clutch on circle track cars? The 5.5" is becoming much more popular nowadays. Why not the 10.5" with a steel flywheel? Why so much money spent on lightweight crankshafts, gun drilled mains don't change the reciprocating mass at all, just the rotating. It's basic physics, whether or not that helps the driver get around the track quicker is dependent upon the driver's skill, but you don't leave parasitic losses sitting on the table if you can help it. Even a hobby stock, short track dirt racer will pick up a noticeable gain going to a lightweight clutch and flywheel.
I don't road race street cars, so I claim 100% ignorance of what is popular with that crowd. I only have experience working in a machine shop building drag and circle track motors. Nobody that is winning any races is ignoring the moment of inertia of their clutch setup.
Don't see why the laws of physics would change for a street car, but I can see how it would be the least important thing for the average weekend warrior doing a track day or taking driving lessons.
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I was just pointing out that a lighter flywheel will not help a Focus much in a street racing environment which is not much different than road track racing. Kinetic energy that can be wisely released upon clutch engagement is not described as a parasitic or frictional loss in my physics book. My bearings are well oiled and show little friction, even with a balanced rotating mass attached.
The majority of your post focuses on dirt/mud racing where max acceleration (power transfer) is achieved through incredibly high wheel slip rates which serve to clear tread, shear soil and create heat. Soil shear tire friction phenomenon is an interesting subject that has nothing to do with asphalt or concrete surfaces. High slip rates are used for dirt circle track, mud swamp buggy or dirt sled pulls by a tractor or truck. These engines need lower rotating mass to help initiate, encourage and maintain a high tire slip condition. Participants that fail to spin tires in dirt come in last place. The higher the slip rate the merrier, so multidisc clutches with smaller diameter are the hot ticket. Greater wheelspeed wins independent of forward velocity, so long as the chassis doesn't go into an underdampened oscillation and begin hopping. However in asphalt road racing where corners and braking is involved, just the opposite is true. Traction suffers when a very modest tire slip rate under accel, decel or cornering is exceeded. The fastest racers avoid wheelspin and they can dance on the edge of traction and manage slip rate. Heavy flywheels aid in this effort, although they do not benefit folks with highest skill levels. Rapid changes in engine speed will lead to tire smoke, loss of grip and reduced acceleration. Again, I'm not talking about drifting or some sport where sustained wheelspin on asphalt is being evaluated as a skill from a controlled skid standpoint. In drag racing, lower rotating mass is good and shifts are almost instantaneous, whether the tranny is considered to be a manual or automatic. These technologies become blurred once technologies merge. Sequential manual transmissions with dry clutches work quite well.
01-13-2013, 12:17 PM
D23 crew- D-Tech- Sedan Revolution= #131
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