Post by oldschool on Mar 6, 2007 23:04:57 GMT
Most of the people are not too sure what the function of the flywheel is about as it serves much more than just one purpose. So it makes sense to describe the function of the flywheel first.
A flywheel is a fairly heavy wheel that is rigidly attached to the crank shaft. Because of its rotary inertia, the flywheel resists changes in the speed of rotation of the shaft; it also can be used to store and deliver mechanical energy on demand (as it was used in some of so called ?eco designs?).
In the 4-stroke reciprocating piston engine the flywheel is used to moderate fluctuations in the rotational speed of the crankshaft, which originate from the transmitted impulses from the pistons to the crankshaft through the connecting rods are intermittent.
Another function of the flywheel in automotive applications is that it acts as the connecting plate between clutch/gearbox and engine, which enables the driver to make a soft start as well as changing gears smoothly. Also it is a convenient piece of engineering to run the starter motor off, which does not necessitate another unit that bears a lot of strength, which means even more weight to be rotated and carried by the vehicle.
Lightening the flywheel increases the torque through to the driveshaft, which relates to an improved performance. The more weight that needs to be set in motion or sped up, the more energy has to be used to accelerate it. This in turn means less power is left to accelerate the rest of the drive train. Also the fact that acceleration is not only determined by the power of the source but also the weight of objects rotating around an axis, a good designer tries to remove the weight from the most beneficial areas (the furthest away from the centre possible) in order to increase the torque output. The best engineering solution is not necessarily to have the lightest flywheel but a flywheel that minimises the loss of torque the most. It is important to understand, however, that top speed will not increase with a lightened flywheel but the car gets there quicker. It is interesting to note that a lightened flywheel helps to gain torque where needed the most, which is at low revs where most of the cars (diesel engines excluded) have comparatively poor performance.
The FIRE engine comes with at least four different clutch plate sizes. All of them can be fitted to any engine with the same bolt hole pattern on the crank shaft. Unfortunately there is than one hole pattern, which are rather similar but not compatible. The peculiar thing is that this is not even in the Fiat spare part listing noted (most likely because it used to be very rare that a flywheel needs replacing on FIRE engines). If you need a replacement flywheel either because it is broken or to lighten it make sure that you take the old one with you to match it. It is unlikely that your scrapyard knows that there is a difference.
When lightening the flywheel it must be clear that it does not only have advantages. The manufacturer actually thought about the design finally used in the car. The heavier the flywheel the smoother the engine runs and the more comfortable is the driving experience. The downside is the much slower response because the higher weight has to be spun up, taking more time, which is taking some power that could be used otherwise to accelerate the vehicle a bit faster.
Another point to consider is the structural integrity. According to Fiat sources the FIRE flywheels are considered to be safe down to 4.7kg. Below this weight it might crack if abused. The meaning of abuse is to have uneccessary clutch slip (wrong clutch adjustment, starting with fully loaded cars, starting from slopes, wear and not fully depressing clutch during acceleration from standstill). The problem that will occur is thermal cracking. The lightest flywheel one of the engineers at clufirepower personally has fitted so far is 1.2kg below this threshold and performing well in a race vehicle. At the moment he is in process to develop an even lighter flywheel but this will be used only in a specific race car.
Anyway 4.7kg is 1.8kg+ taken from the original weight, which makes a considerable difference when the weight is taken from the right places. The further out it is taken away the better. Unfortunately this is only possible to a limited degree because the ring gear for the starter motor needs sufficient support to start the engine safely day in day out.
After the lightening has been finished it is an absolute must to balance the flywheel. This has to be done regardless whether the engine is rebuilt or the flywheel has been lightened on its own. Failing to do so will almost certainly end in a destruction of the engine.
When refitting the FIRE flywheels a torque setting of 40Nm has to be applied. The bolts should be tightened crosswise and the use of thread lock is more than recommended. When fitting the clutch it is advisable to use thread lock too. If the flywheel is used in an extreme situation it should be balanced first on its own and afterwards with the clutch fitted and of course when an engine rebuilt has been done it would be balanced with the crank, pistons and conrods.
A flywheel is a fairly heavy wheel that is rigidly attached to the crank shaft. Because of its rotary inertia, the flywheel resists changes in the speed of rotation of the shaft; it also can be used to store and deliver mechanical energy on demand (as it was used in some of so called ?eco designs?).
In the 4-stroke reciprocating piston engine the flywheel is used to moderate fluctuations in the rotational speed of the crankshaft, which originate from the transmitted impulses from the pistons to the crankshaft through the connecting rods are intermittent.
Another function of the flywheel in automotive applications is that it acts as the connecting plate between clutch/gearbox and engine, which enables the driver to make a soft start as well as changing gears smoothly. Also it is a convenient piece of engineering to run the starter motor off, which does not necessitate another unit that bears a lot of strength, which means even more weight to be rotated and carried by the vehicle.
Lightening the flywheel increases the torque through to the driveshaft, which relates to an improved performance. The more weight that needs to be set in motion or sped up, the more energy has to be used to accelerate it. This in turn means less power is left to accelerate the rest of the drive train. Also the fact that acceleration is not only determined by the power of the source but also the weight of objects rotating around an axis, a good designer tries to remove the weight from the most beneficial areas (the furthest away from the centre possible) in order to increase the torque output. The best engineering solution is not necessarily to have the lightest flywheel but a flywheel that minimises the loss of torque the most. It is important to understand, however, that top speed will not increase with a lightened flywheel but the car gets there quicker. It is interesting to note that a lightened flywheel helps to gain torque where needed the most, which is at low revs where most of the cars (diesel engines excluded) have comparatively poor performance.
The FIRE engine comes with at least four different clutch plate sizes. All of them can be fitted to any engine with the same bolt hole pattern on the crank shaft. Unfortunately there is than one hole pattern, which are rather similar but not compatible. The peculiar thing is that this is not even in the Fiat spare part listing noted (most likely because it used to be very rare that a flywheel needs replacing on FIRE engines). If you need a replacement flywheel either because it is broken or to lighten it make sure that you take the old one with you to match it. It is unlikely that your scrapyard knows that there is a difference.
When lightening the flywheel it must be clear that it does not only have advantages. The manufacturer actually thought about the design finally used in the car. The heavier the flywheel the smoother the engine runs and the more comfortable is the driving experience. The downside is the much slower response because the higher weight has to be spun up, taking more time, which is taking some power that could be used otherwise to accelerate the vehicle a bit faster.
Another point to consider is the structural integrity. According to Fiat sources the FIRE flywheels are considered to be safe down to 4.7kg. Below this weight it might crack if abused. The meaning of abuse is to have uneccessary clutch slip (wrong clutch adjustment, starting with fully loaded cars, starting from slopes, wear and not fully depressing clutch during acceleration from standstill). The problem that will occur is thermal cracking. The lightest flywheel one of the engineers at clufirepower personally has fitted so far is 1.2kg below this threshold and performing well in a race vehicle. At the moment he is in process to develop an even lighter flywheel but this will be used only in a specific race car.
Anyway 4.7kg is 1.8kg+ taken from the original weight, which makes a considerable difference when the weight is taken from the right places. The further out it is taken away the better. Unfortunately this is only possible to a limited degree because the ring gear for the starter motor needs sufficient support to start the engine safely day in day out.
After the lightening has been finished it is an absolute must to balance the flywheel. This has to be done regardless whether the engine is rebuilt or the flywheel has been lightened on its own. Failing to do so will almost certainly end in a destruction of the engine.
When refitting the FIRE flywheels a torque setting of 40Nm has to be applied. The bolts should be tightened crosswise and the use of thread lock is more than recommended. When fitting the clutch it is advisable to use thread lock too. If the flywheel is used in an extreme situation it should be balanced first on its own and afterwards with the clutch fitted and of course when an engine rebuilt has been done it would be balanced with the crank, pistons and conrods.
