Race Clutch
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Originally Posted by Asura,Nov 15 2006, 08:26 AM
The ATS destroyed the transmission synchros on Karner's car.
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Originally Posted by EternalShadowAW,Oct 3 2007, 01:34 PM
anyway to strengthen the synchros to prevent the problem (potential)? Or can you get tougher synchros? I'm a complete noob when regarding transmission parts, sorry
No seriously guys: If the mass of the flywheel is irrelevant for acceleration, why is saving 20 grams on the piston worthwhile (other than load on the rod of course)? Why lighter drivetrain at all?
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From: Toronto, Canada
Originally Posted by INTJ,Oct 3 2007, 05:47 PM
No seriously guys: If the mass of the flywheel is irrelevant for acceleration, why is saving 20 grams on the piston worthwhile (other than load on the rod of course)? Why lighter drivetrain at all?
It's pretty basic physics, Newton's 2nd law actually: F=ma force equals mass times acceleration which can be restarted a=F/m -- acceleration (a) = force (F) divided by mass (m). Thus keeping F the same (the energy of the fuel burn) and reducing m will increase the acceleration of the piston.
Same for the flywheel, reducing mass will increase the acceleration of the flywheel with the same amount of force (coming from blipping the engine).
What kills your synchros has nothing to do with the clutch specifically. It's the amount of energy you dissipate through them to synchronize gear speeds. A clutch which bites hard is forcing the synchros to do all of the work as opposed to a softer clutch which drags and absorbs much of the energy.
The S2000 has double synchros on gears 1-4 and single synchros on gears 5 and 6. Honda didn't design the transmission for repeated shifts from the redline in 4th to 5th or the redline in 5th to sixth that you might experience in racing but not on the street. Redline of 4th is close to 120MPH. Synchros have always been a weak link. Honda has twice tried to solve the problem, once my moving to carbon synchros instead of brass (which can absorb far more energy) and by slowing down the clutch slave cylinder allowing more clutch drag even when dropped hard.
When you have a grippy clutch rev matching is critical because of the load you are putting on the synchros, especially on 4-5 and 5-6 shifts which have only a single synchro.
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From: St. Louis
I am going to have to disagree here. It is a simple matter of F=ma. And losing mass on any part of of the drivetrain is going to increase the accelration of the drivetrain. This is expecially true in lower gears at lower speeds, where accelerating the mass of the vehicle is the limiting factor versus overcoming the drag of the vehicle.
It is true that lightening the flywheel produces no extra steady state horsepower. It is also true that lightening engine components in itself produces no extra steady state horsepower, but does tend to allow the engine to rev higher, which creates more horsepower. However, lightening any component of the drivetrain from the pistons to the tires decreases your reciprocating mass, and increases acceleration. The only time it would not is when air resistance is so forceful that the acceleration can be approximated to be steady state. I doubt these conditions are reached in a race.
Keep in mind that the flywheel is also not geared down like the rest of the drivetrain behind the transmission. At gears below overdrive, it is required to spin faster, and therefore accelerate more than say the wheels and tires. So for instance, while at redline in second gear (calculated 78mph based on gear ratios and tire height) the rear wheels are rotating at about 1062 rpm, but the F20C and attached flywheel are at at 9000 rpm. This difference reduces as the gears go higher (and for of course for BSP or SM2 autcrossers, the effect increases in first gear).
Now of course moment of inertia and mass are two seprate things. Loosing 6lbs of your flywheel is not the same as loosing 6lbs of your wheels or tires because of the shorter moment arm. But lets estimate that you lose this 6lbs of your flywheel at an average distance of 3" (halfway up the radius of a 12" diamater flywheel), or 1/4'.
I = mr^2 = 6lbs * (1/4)^2 = 0.375 lbs*ft^2
If we lose the same 6lbs of a wheel, let's say centered at a radius of 4 inches (halfway up 16" diamater wheel) or 1/3'
I = mr^2 = 6lbs * (1/3)^2 = 0.67 lbs*ft^2
So we get almost twice the benefit from lightening a wheel as the flywheel. Now multiply that by four assuming you get a complete set of lightweight wheels. You now get 8 times the benefit.
But wait! Now we have to leave the simple F=ma and go to the rotational version, Angular Acceleration = Moment of Inertia * Torque. As we calculated above, in second gear, the wheels see a 9 times torque multiplier that the flywheel does not. Since 9 > 8, the flywheel actually makes a bigger difference in acceleration (angular acceleration being converted to the car's linear acceleration through the simple machine called a wheel).
Of course this is all theoretical and results will vary with actual mass and moment arms, but it's at least on the same order of magnitude as weight loss in the wheels. I was not convinced myself before I did the calculations, but it appears that if we assume lightweight wheels have an effect on acceleration, so must a lightweight flywheel and clutch assembly.
It is true that lightening the flywheel produces no extra steady state horsepower. It is also true that lightening engine components in itself produces no extra steady state horsepower, but does tend to allow the engine to rev higher, which creates more horsepower. However, lightening any component of the drivetrain from the pistons to the tires decreases your reciprocating mass, and increases acceleration. The only time it would not is when air resistance is so forceful that the acceleration can be approximated to be steady state. I doubt these conditions are reached in a race.
Keep in mind that the flywheel is also not geared down like the rest of the drivetrain behind the transmission. At gears below overdrive, it is required to spin faster, and therefore accelerate more than say the wheels and tires. So for instance, while at redline in second gear (calculated 78mph based on gear ratios and tire height) the rear wheels are rotating at about 1062 rpm, but the F20C and attached flywheel are at at 9000 rpm. This difference reduces as the gears go higher (and for of course for BSP or SM2 autcrossers, the effect increases in first gear).
Now of course moment of inertia and mass are two seprate things. Loosing 6lbs of your flywheel is not the same as loosing 6lbs of your wheels or tires because of the shorter moment arm. But lets estimate that you lose this 6lbs of your flywheel at an average distance of 3" (halfway up the radius of a 12" diamater flywheel), or 1/4'.
I = mr^2 = 6lbs * (1/4)^2 = 0.375 lbs*ft^2
If we lose the same 6lbs of a wheel, let's say centered at a radius of 4 inches (halfway up 16" diamater wheel) or 1/3'
I = mr^2 = 6lbs * (1/3)^2 = 0.67 lbs*ft^2
So we get almost twice the benefit from lightening a wheel as the flywheel. Now multiply that by four assuming you get a complete set of lightweight wheels. You now get 8 times the benefit.
But wait! Now we have to leave the simple F=ma and go to the rotational version, Angular Acceleration = Moment of Inertia * Torque. As we calculated above, in second gear, the wheels see a 9 times torque multiplier that the flywheel does not. Since 9 > 8, the flywheel actually makes a bigger difference in acceleration (angular acceleration being converted to the car's linear acceleration through the simple machine called a wheel).
Of course this is all theoretical and results will vary with actual mass and moment arms, but it's at least on the same order of magnitude as weight loss in the wheels. I was not convinced myself before I did the calculations, but it appears that if we assume lightweight wheels have an effect on acceleration, so must a lightweight flywheel and clutch assembly.
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Are you trying to confuse me on purpose?
First you disagree with me, then you agree, then you disagree quoting back the exact same formula I used saying the weight of the flywheel matters only to go on to show that a 6lb reduction is rotating mass in a single wheel has 2x the effect compared to the flywheel, 4x if you include both wheels, highlighting the very point I was making in the first place: a 6lb reduction in the weight of the flywheel results in a 0.375 lb/ft increase in torque output or 0.25% the total torque output of the engine.
Insignificant, technically, practically or any other way you look at it when it comes to vehicle acceleration. Significant in engine acceleration with the drive train detached.
First you disagree with me, then you agree, then you disagree quoting back the exact same formula I used saying the weight of the flywheel matters only to go on to show that a 6lb reduction is rotating mass in a single wheel has 2x the effect compared to the flywheel, 4x if you include both wheels, highlighting the very point I was making in the first place: a 6lb reduction in the weight of the flywheel results in a 0.375 lb/ft increase in torque output or 0.25% the total torque output of the engine.
Insignificant, technically, practically or any other way you look at it when it comes to vehicle acceleration. Significant in engine acceleration with the drive train detached.
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From: Toronto, Canada
Lightweight wheels have more benefits beyond simple rotational mass. A 6lb reduction in the weight of a wheel is a 24lb reduction in unsprung weight and a reduction in rotational mass. The rotational mass gain may be insignificant at lower gears but it matters in higher gears where rolling resistance and drag come into play. On a race track 2nd gear is used sparingly, first gear never. Since this is a racing clutch discussion it has to be within the context of racing on a track. I still think it's just as meaningless as the clutch/flywheel weight.
If anything you are saying that reduction of the rotational mass of the entire drivetrain represents a ~ 1-2% loss of torque. 1.5-3.0 lb/ft. I didn't say lighter wheels had benefits in vehicle acceleration. I said a lighter flywheel had no tangible effect. Added together you can reduce the drivetrain loss by about 1.5 lb/ft.
If anything you are saying that reduction of the rotational mass of the entire drivetrain represents a ~ 1-2% loss of torque. 1.5-3.0 lb/ft. I didn't say lighter wheels had benefits in vehicle acceleration. I said a lighter flywheel had no tangible effect. Added together you can reduce the drivetrain loss by about 1.5 lb/ft.
