Light weight flywheels
25 August 2001, 07:45 PM
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Or is that just the map I'm trying?
Come on Danny how long do you need, it can't be that hard for an "IT bod".
You've been playing with it (& the Link)since I met you in ? April.
Come on Danny how long do you need, it can't be that hard for an "IT bod".
You've been playing with it (& the Link)since I met you in ? April.
27 August 2001, 08:01 AM
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Danny,
given that your flywheel is so light why don't you set the idle speed to 1200 or so instead of 800.
This is one of the reasons race cars have high idle speeds - the flywheel can't support the normal idle.
Trout
given that your flywheel is so light why don't you set the idle speed to 1200 or so instead of 800.
This is one of the reasons race cars have high idle speeds - the flywheel can't support the normal idle.
Trout
28 August 2001, 12:10 AM
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Mark,
4.5Kg is nothing for a flywheel, and I'd suggest that this is much too light for a car which will be driven in traffic regularly.
I have found that you can drive around the loss of torque at low rpm easily if you don't go too far. Actually, the engine's torque output is not directly affected by lightening the flywheel - it is that after lightening the flywheel's intertia doesn't contribtute enough torque to mask the fact that the engine produces naff-all torque just off idle. Of course its not a problem if you don't mind using 4000rpm to get into / out of that parking space
.
Race engines are also affected by the fact that they have been tuned to maximise VE at the top end of the rpm range and because of this, gas velocity off idle is too low and efficiency is poor which totally kills the low end.
I would like my next flywheel to be lighened by around 25-30% from stock. This will improve gearchanging and acceleration (slightly) without making it a nightmare to drive day to day.
Cheers,
Alex
4.5Kg is nothing for a flywheel, and I'd suggest that this is much too light for a car which will be driven in traffic regularly.
I have found that you can drive around the loss of torque at low rpm easily if you don't go too far. Actually, the engine's torque output is not directly affected by lightening the flywheel - it is that after lightening the flywheel's intertia doesn't contribtute enough torque to mask the fact that the engine produces naff-all torque just off idle. Of course its not a problem if you don't mind using 4000rpm to get into / out of that parking space
.Race engines are also affected by the fact that they have been tuned to maximise VE at the top end of the rpm range and because of this, gas velocity off idle is too low and efficiency is poor which totally kills the low end.
I would like my next flywheel to be lighened by around 25-30% from stock. This will improve gearchanging and acceleration (slightly) without making it a nightmare to drive day to day.
Cheers,
Alex
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29 August 2001, 03:40 AM
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A very light flywheel will be an advantage down low in performance and a disadvantage up high and on the in the other respect a heavier flywheel acts in an opposite fashion. If you consider this theory and testing the ideal weight is 6.67 kg's which is ideal for torque and max revability.
I saw one the other day that had counter sunk holes to allow gases to escape which means less slippage, but can't remember where.
Dan
[This message has been edited by submannz (edited 29 August 2001).]
I saw one the other day that had counter sunk holes to allow gases to escape which means less slippage, but can't remember where.
Dan
[This message has been edited by submannz (edited 29 August 2001).]
29 August 2001, 04:38 PM
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Surely this is the wrong way around?
The flywheels primary function is to smooth out the engine's torque delivery, especially at low engine speeds. Reducing flywheel mass and therefore inertia will cause loss of low eng smoothness and torque delivery (less rotational inertia to fill the gaps) but higher engine speeds will gain from the reduction in inertial drag (if that's the right term).
Race cars, IIRC, tend to run lighter flywheels and are tuned for maximum (reliable) mid to top end power.
Moray
The flywheels primary function is to smooth out the engine's torque delivery, especially at low engine speeds. Reducing flywheel mass and therefore inertia will cause loss of low eng smoothness and torque delivery (less rotational inertia to fill the gaps) but higher engine speeds will gain from the reduction in inertial drag (if that's the right term).
Race cars, IIRC, tend to run lighter flywheels and are tuned for maximum (reliable) mid to top end power.
Moray
29 August 2001, 05:31 PM
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Hi,
I think this could be argued from either perspective... I tend to agree with Moray though
A heavy flywheel will contribute to getting the car off the line as it's rotational momentum is added to the total torque of the engine at those rpm, giving more total torque. Most cars with a very light flywheel are very easy to stall unless you use more revs to compensate.
On the other hand, a light flywheel is easier for the engine to accelerate when it's torque output is lowest i.e. at low rpm, so less weight allows the engine to accelerate faster - not just at low RPM but throughout the rev range.
I can't imagine that a heavy flywheel will ever improve acceleration at high rpm - it is effectively more or less redundant at high rpm. This is why race engines have very light flywheels and a fast tickover to allow them to idle.
The trade off is between easy drivability and improved acceleration.. for most road cars I wouldn't want to go much more than 30% lighter, but this is also affected by the mass distribution of the flywheel. More weight at the outer edge will help retain rotational intertia while reducing total weight.
Having done this to a few previous cars I can confirm that it does improve acceleration a bit, improves 'blipability', and feels more sporty. Go too far and you'll regret it though.
Cheers,
Alex
I think this could be argued from either perspective... I tend to agree with Moray though
A heavy flywheel will contribute to getting the car off the line as it's rotational momentum is added to the total torque of the engine at those rpm, giving more total torque. Most cars with a very light flywheel are very easy to stall unless you use more revs to compensate.
On the other hand, a light flywheel is easier for the engine to accelerate when it's torque output is lowest i.e. at low rpm, so less weight allows the engine to accelerate faster - not just at low RPM but throughout the rev range.
I can't imagine that a heavy flywheel will ever improve acceleration at high rpm - it is effectively more or less redundant at high rpm. This is why race engines have very light flywheels and a fast tickover to allow them to idle.
The trade off is between easy drivability and improved acceleration.. for most road cars I wouldn't want to go much more than 30% lighter, but this is also affected by the mass distribution of the flywheel. More weight at the outer edge will help retain rotational intertia while reducing total weight.
Having done this to a few previous cars I can confirm that it does improve acceleration a bit, improves 'blipability', and feels more sporty. Go too far and you'll regret it though.
Cheers,
Alex
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