Lets talk about clutches
01-26-2011, 07:04 PM
#81
In drag racing, it is critical. Every 0.01 in 60' time is worth 1.5 to 2 times what the 60' netted in total elapsed time.
The problem is if the clutch pack is so light that the car bogs off the line, the clutch is too light. If you have enough torque to motor away without dropping rpms, than you will be ok.
Another concern is that when staging, you have to burn a light, then creep forward to burn another light. If the car is so jumpy that you go past the light, the race is over, you lose. Even the most radical drag cars can smoothly position themselves at the line.
The problem is if the clutch pack is so light that the car bogs off the line, the clutch is too light. If you have enough torque to motor away without dropping rpms, than you will be ok.
Another concern is that when staging, you have to burn a light, then creep forward to burn another light. If the car is so jumpy that you go past the light, the race is over, you lose. Even the most radical drag cars can smoothly position themselves at the line.
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01-26-2011, 10:30 PM
#82
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Bob, any chance you could measure or calculate the spring rate?
http://www.engineersedge.com/spring_comp_calc_k.htm
calculate individual spring force:
F = T/(r*n)
(where r is the radius to the spring centerline, T is torque, n is num springs)
calculate spring displacement
x = F/k
(x = displacement at force, k = spring rate, calculated above)
and then (spring installed length - spring block height (fully compressed))
to see if the spring is partially compressed, fully compressed, or just plain smashed immediately.
ie I'm curious if they do anything.
http://www.engineersedge.com/spring_comp_calc_k.htm
calculate individual spring force:
F = T/(r*n)
(where r is the radius to the spring centerline, T is torque, n is num springs)
calculate spring displacement
x = F/k
(x = displacement at force, k = spring rate, calculated above)
and then (spring installed length - spring block height (fully compressed))
to see if the spring is partially compressed, fully compressed, or just plain smashed immediately.
ie I'm curious if they do anything.
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01-27-2011, 12:37 PM
#83
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FWIW I rode in a friend's car this week, a high HP turboed Miata, that has a multi-disc clutch very similar to what is described below. It is not streetable IMO, in the sense that you could make it work but it would be really, really hard to use in stop-go traffic. The car is very tricky to launch since the clutch is very difficult to modulate. I have had a 6-puck in my car and this clutch is much worse on modulation, like Bob said it is an on-off switch.
You will also be a ricer magnet because every time you leave a stoplight you will look like you are trying to race someone. Rev engine, 'dump' clutch (whether or not you want to dump), spin tires. Maybe you could double or triple clutch it to get the car rolling a bit before complete engagement, but again that is not very streetable.
Think of that episode of Top Gear when they let the Stig drive an actual F1 car. He stalled it on launch. Hammond did the same thing. Same deal, multi-disc clutch, albeit the F1 clutch is supposedly really hard to use. I am generalizing here but you get the idea.
Maybe with organic plates it would be better. Emilio says his multi-disc clutch is streetable with the organic discs.
You will also be a ricer magnet because every time you leave a stoplight you will look like you are trying to race someone. Rev engine, 'dump' clutch (whether or not you want to dump), spin tires. Maybe you could double or triple clutch it to get the car rolling a bit before complete engagement, but again that is not very streetable.
Think of that episode of Top Gear when they let the Stig drive an actual F1 car. He stalled it on launch. Hammond did the same thing. Same deal, multi-disc clutch, albeit the F1 clutch is supposedly really hard to use. I am generalizing here but you get the idea.
Maybe with organic plates it would be better. Emilio says his multi-disc clutch is streetable with the organic discs.
I've driven a GT4 Bugey Sprite with a 5.5 Tilton. It was drivable for me if you always were launching hard. Kind of an on off switch. It wouldn’t handle much stop and go without overheating it though. It would probably need frequent disk replacement if you drove it on the street.
FWIW Mazdamotorsports sells 3 versions of flywheels for the 5.5" clutch. Steel with an aluminum ring gear ~4 lbs for the flywheel. A Tilton ceremetalic twin Rally clutch to fit it weighs 6.1 lbs and holds 500 ft-lbs.
I suspect getting the car rolling from a stop would often involve some wheel spinage with that setup.
Bob
FWIW Mazdamotorsports sells 3 versions of flywheels for the 5.5" clutch. Steel with an aluminum ring gear ~4 lbs for the flywheel. A Tilton ceremetalic twin Rally clutch to fit it weighs 6.1 lbs and holds 500 ft-lbs.
I suspect getting the car rolling from a stop would often involve some wheel spinage with that setup.
Bob
Last edited by ZX-Tex; 01-27-2011 at 01:52 PM.
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02-01-2011, 11:02 PM
#84
Yeah, post the above is about my new car which has a Quartermaster 7.25" twin disc. I'm getting a little more used to it...we'll see how long I stick with it. I am more worried about day to day wear in traffic than the drivability issues. I contacted QM about replacement clutch disc options but haven't heard anything back yet. They only list one part number on their site.
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