flywheels - a quick question
Discussion
what's the difference between an LS1 and LS7 flywheel ?
going to invest in an aluminium flywheel, but the car already has LS7 clutch in it. Now, I assume that this has involved a change of flywheel, too, but want to make sure before I order one.
so, if I've got an LS7 clutch in the car, my replacement must be an LS7 flywheel. Correct ?
going to invest in an aluminium flywheel, but the car already has LS7 clutch in it. Now, I assume that this has involved a change of flywheel, too, but want to make sure before I order one.
so, if I've got an LS7 clutch in the car, my replacement must be an LS7 flywheel. Correct ?
MyM8V8 said:
stevieturbo said:
Although I woudlnt be fitting a lightweight flywheel at all, unless there was very good reason to do so.
What type of vehicle is it in ? what sort of weight etc ?
Why not? Lower MOI, better throttle response, better engine braking?What type of vehicle is it in ? what sort of weight etc ?
If you're scraping the barrel on a lightweight car with very short gearing, lacklustre engine power, then perhaps yes its a worthwhile mod.
IMO the difference it would make to a big heavy car like a Monaro or similar, would not be positive.
I certainly wouldnt use a lightweight flywheel unless I absolutely had to ( which I do...but the weight of the clutch almost makes up for it lol )
i would agree with stevie on this one,a light weight flywheel can aslo cause drive line vibes and make the gearbox sound like a bag of spanners,twin plate set ups use a lighter one but then there is more mass in the rest of it, dont fit a under drive pulley either as they can cause all sorts of problems. the only time you really notice a light flywheel is revving in idle anyway,
Depends on how the clutch is built. Benefits are real. But as per below proportional to the weight of the vehicle as Stevie aludes to.
"No one ever said that a lightened flywheel would increase horsepower, but it sure does *decrease* acceleration times. Herb Adams, in his book CHASSIS ENGINEERING, says that "..the effect of reducing rotational inertia on driveline parts has 15 times the benefit of just reducing the weight of the car." I have been intrigued with this statement for months, and wish that I had followed his suggestion a long time ago and gone to a lightened flywheel. I am not an engineer (obviously), but I do have enough seat time to have a fairly refined butt dyno, and I can tell you that the difference in how the engine spools up is not subtle, but positively sensational. I wish that I had done some quarter mile times (yeah, sure, I go to the drags all the time) before I installed my lightened flywheel, so that I could provide reliable, numerical evidence. I didn't, so believe what you choose, but I can think of absolutely no reason NOT to go to the lightened flywheel. It is the single most important modification that I have made in quite a while, and I have made quite a few.
As far as perceived acceleration goes, your engine sees the mass of your car as a point stuck way out on some lever arm that it has to twist. If your engine is direct drive (i.e. no gear reduction), and you have an M3, you'd need quite a bit of torque to get that 3175 lbs moving faster. So somebody invented gears, which has the effect of changing the length of the lever, as far as the engine is concerned. In an M3, for example, first gear is 4.20:1 and final drive is 3.23:1 so what looked like 3175 lbs to the engine out at the end of that lever without gear reduction now looks more like 234 lbs (3175/13.57), assuming your rear tire has a radius of one foot give or take a few inches.
Suppose you had a magic flywheel with all the mass concentrated at the outer edge. Now the flywheel is stuck directly to the engine, so you can't reduce its effective moment via gearing. The only way you can reduce the moment is by lightening it and/or changing its mass distribution. If you could somehow remove 10 lbs from the rim of the flywheel, and the flywheel's radius was also one foot, then that would have the same effect on acceleration in first gear as reducing the mass of the car by 10x13.57 or 135.7 pounds. Now I am guessing the flywheel's radius is more like six to eight inches or so, so 10 pounds off it's outer edge would have the same effect as reducing the car's mass by more like 70-100 pounds (in first gear). Only you can't take that much weight off the edge, and moments of disks look more like 1/2mr^2, etc. etc. Point is that in first gear, the mass of your car appears to be only 20-30 times that of 10 pounds out at the edge of your flywheel, as far as the engine can tell. So the reduction of weight of the flywheel begins to be pretty significant. Expect bigtime effective acceleration improvements in first gear for proper flywheel lightening, similar to what you'd expect from reducing the weight of the car by anywhere from 70 to 100 lbs or more. The benefits decrease in higher gears in proportion to whatever the ratio is.
Obviously, the lighter your car is to begin with, the bigger an acceleration improvement you'll see since the flywheel mass represents a larger portion of the perceived mass of the car."
"No one ever said that a lightened flywheel would increase horsepower, but it sure does *decrease* acceleration times. Herb Adams, in his book CHASSIS ENGINEERING, says that "..the effect of reducing rotational inertia on driveline parts has 15 times the benefit of just reducing the weight of the car." I have been intrigued with this statement for months, and wish that I had followed his suggestion a long time ago and gone to a lightened flywheel. I am not an engineer (obviously), but I do have enough seat time to have a fairly refined butt dyno, and I can tell you that the difference in how the engine spools up is not subtle, but positively sensational. I wish that I had done some quarter mile times (yeah, sure, I go to the drags all the time) before I installed my lightened flywheel, so that I could provide reliable, numerical evidence. I didn't, so believe what you choose, but I can think of absolutely no reason NOT to go to the lightened flywheel. It is the single most important modification that I have made in quite a while, and I have made quite a few.
As far as perceived acceleration goes, your engine sees the mass of your car as a point stuck way out on some lever arm that it has to twist. If your engine is direct drive (i.e. no gear reduction), and you have an M3, you'd need quite a bit of torque to get that 3175 lbs moving faster. So somebody invented gears, which has the effect of changing the length of the lever, as far as the engine is concerned. In an M3, for example, first gear is 4.20:1 and final drive is 3.23:1 so what looked like 3175 lbs to the engine out at the end of that lever without gear reduction now looks more like 234 lbs (3175/13.57), assuming your rear tire has a radius of one foot give or take a few inches.
Suppose you had a magic flywheel with all the mass concentrated at the outer edge. Now the flywheel is stuck directly to the engine, so you can't reduce its effective moment via gearing. The only way you can reduce the moment is by lightening it and/or changing its mass distribution. If you could somehow remove 10 lbs from the rim of the flywheel, and the flywheel's radius was also one foot, then that would have the same effect on acceleration in first gear as reducing the mass of the car by 10x13.57 or 135.7 pounds. Now I am guessing the flywheel's radius is more like six to eight inches or so, so 10 pounds off it's outer edge would have the same effect as reducing the car's mass by more like 70-100 pounds (in first gear). Only you can't take that much weight off the edge, and moments of disks look more like 1/2mr^2, etc. etc. Point is that in first gear, the mass of your car appears to be only 20-30 times that of 10 pounds out at the edge of your flywheel, as far as the engine can tell. So the reduction of weight of the flywheel begins to be pretty significant. Expect bigtime effective acceleration improvements in first gear for proper flywheel lightening, similar to what you'd expect from reducing the weight of the car by anywhere from 70 to 100 lbs or more. The benefits decrease in higher gears in proportion to whatever the ratio is.
Obviously, the lighter your car is to begin with, the bigger an acceleration improvement you'll see since the flywheel mass represents a larger portion of the perceived mass of the car."
Edited by ringram on Tuesday 9th March 08:48
ringram said:
Depends on how the clutch is built. Benefits are real. But as per below proportional to the weight of the vehicle as Stevie aludes to.
"No one ever said that a lightened flywheel would increase horsepower, but it sure does *decrease* acceleration times. Herb Adams, in his book CHASSIS ENGINEERING, says that "..the effect of reducing rotational inertia on driveline parts has 15 times the benefit of just reducing the weight of the car." I have been intrigued with this statement for months, and wish that I had followed his suggestion a long time ago and gone to a lightened flywheel. I am not an engineer (obviously), but I do have enough seat time to have a fairly refined butt dyno, and I can tell you that the difference in how the engine spools up is not subtle, but positively sensational. I wish that I had done some quarter mile times (yeah, sure, I go to the drags all the time) before I installed my lightened flywheel, so that I could provide reliable, numerical evidence. I didn't, so believe what you choose, but I can think of absolutely no reason NOT to go to the lightened flywheel. It is the single most important modification that I have made in quite a while, and I have made quite a few.
As far as perceived acceleration goes, your engine sees the mass of your car as a point stuck way out on some lever arm that it has to twist. If your engine is direct drive (i.e. no gear reduction), and you have an M3, you'd need quite a bit of torque to get that 3175 lbs moving faster. So somebody invented gears, which has the effect of changing the length of the lever, as far as the engine is concerned. In an M3, for example, first gear is 4.20:1 and final drive is 3.23:1 so what looked like 3175 lbs to the engine out at the end of that lever without gear reduction now looks more like 234 lbs (3175/13.57), assuming your rear tire has a radius of one foot give or take a few inches.
Suppose you had a magic flywheel with all the mass concentrated at the outer edge. Now the flywheel is stuck directly to the engine, so you can't reduce its effective moment via gearing. The only way you can reduce the moment is by lightening it and/or changing its mass distribution. If you could somehow remove 10 lbs from the rim of the flywheel, and the flywheel's radius was also one foot, then that would have the same effect on acceleration in first gear as reducing the mass of the car by 10x13.57 or 135.7 pounds. Now I am guessing the flywheel's radius is more like six to eight inches or so, so 10 pounds off it's outer edge would have the same effect as reducing the car's mass by more like 70-100 pounds (in first gear). Only you can't take that much weight off the edge, and moments of disks look more like 1/2mr^2, etc. etc. Point is that in first gear, the mass of your car appears to be only 20-30 times that of 10 pounds out at the edge of your flywheel, as far as the engine can tell. So the reduction of weight of the flywheel begins to be pretty significant. Expect bigtime effective acceleration improvements in first gear for proper flywheel lightening, similar to what you'd expect from reducing the weight of the car by anywhere from 70 to 100 lbs or more. The benefits decrease in higher gears in proportion to whatever the ratio is.
Obviously, the lighter your car is to begin with, the bigger an acceleration improvement you'll see since the flywheel mass represents a larger portion of the perceived mass of the car."
And if you are building a performance car for acceleration (what else would you build it for?), that goes for everything that rotates, not just the flywheel."No one ever said that a lightened flywheel would increase horsepower, but it sure does *decrease* acceleration times. Herb Adams, in his book CHASSIS ENGINEERING, says that "..the effect of reducing rotational inertia on driveline parts has 15 times the benefit of just reducing the weight of the car." I have been intrigued with this statement for months, and wish that I had followed his suggestion a long time ago and gone to a lightened flywheel. I am not an engineer (obviously), but I do have enough seat time to have a fairly refined butt dyno, and I can tell you that the difference in how the engine spools up is not subtle, but positively sensational. I wish that I had done some quarter mile times (yeah, sure, I go to the drags all the time) before I installed my lightened flywheel, so that I could provide reliable, numerical evidence. I didn't, so believe what you choose, but I can think of absolutely no reason NOT to go to the lightened flywheel. It is the single most important modification that I have made in quite a while, and I have made quite a few.
As far as perceived acceleration goes, your engine sees the mass of your car as a point stuck way out on some lever arm that it has to twist. If your engine is direct drive (i.e. no gear reduction), and you have an M3, you'd need quite a bit of torque to get that 3175 lbs moving faster. So somebody invented gears, which has the effect of changing the length of the lever, as far as the engine is concerned. In an M3, for example, first gear is 4.20:1 and final drive is 3.23:1 so what looked like 3175 lbs to the engine out at the end of that lever without gear reduction now looks more like 234 lbs (3175/13.57), assuming your rear tire has a radius of one foot give or take a few inches.
Suppose you had a magic flywheel with all the mass concentrated at the outer edge. Now the flywheel is stuck directly to the engine, so you can't reduce its effective moment via gearing. The only way you can reduce the moment is by lightening it and/or changing its mass distribution. If you could somehow remove 10 lbs from the rim of the flywheel, and the flywheel's radius was also one foot, then that would have the same effect on acceleration in first gear as reducing the mass of the car by 10x13.57 or 135.7 pounds. Now I am guessing the flywheel's radius is more like six to eight inches or so, so 10 pounds off it's outer edge would have the same effect as reducing the car's mass by more like 70-100 pounds (in first gear). Only you can't take that much weight off the edge, and moments of disks look more like 1/2mr^2, etc. etc. Point is that in first gear, the mass of your car appears to be only 20-30 times that of 10 pounds out at the edge of your flywheel, as far as the engine can tell. So the reduction of weight of the flywheel begins to be pretty significant. Expect bigtime effective acceleration improvements in first gear for proper flywheel lightening, similar to what you'd expect from reducing the weight of the car by anywhere from 70 to 100 lbs or more. The benefits decrease in higher gears in proportion to whatever the ratio is.
Obviously, the lighter your car is to begin with, the bigger an acceleration improvement you'll see since the flywheel mass represents a larger portion of the perceived mass of the car."
Edited by ringram on Tuesday 9th March 08:48
From personal experience the lack of inertia with a lightweight flywheel can make the car much harder to get off the line smoothly, and there is a significant drop in RPM between gear changes. This obviously depends on just how much lighter you go.
On the plus side a lighter flywheel makes the car much more responsive. It really depends what you want to use the car for.
On the plus side a lighter flywheel makes the car much more responsive. It really depends what you want to use the car for.
ringram said:
"Expect bigtime effective acceleration improvements in first gear for proper flywheel lightening, similar to what you'd expect from reducing the weight of the car by anywhere from 70 to 100 lbs or more. The benefits decrease in higher gears in proportion to whatever the ratio is.
Hmmm, done some calcs on this.
Roughly, if I was to drive with between 10-28 litres in the fuel tank (the maths equiv of reducing the car weight by 70-100 lbs) I would have the same benefits as someone with a full tank and a lightened flywheel???
Seems a cheaper option to me....?
(Based on Tank holding 70 Litres, Fuel weighs .75kg/l, 1kg=2.2lbs)
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