Clutch guys

[joespanova]

I'm not sure I'm getting what I expected out of the initial question.......clutch management wasn't the consideration here. Specifically , you could make the clutch work at a variety of RPMs......my consideration was the connection between "that" and making it work around / at / near , the aforementioned hypothetical engine torque / power point. In other words is the effort (through clutch tuning) made to "exploit" the engines peak points of either or just manage it to get the car to work with little regard to either.
Using my own as an example , with no change in the bell housing and enough base ( because I don't use a data logger ) to launch the car well enough to keep me near or well into decent 60 fts. I can apparently spin or wheel stand just by varying launch RPM. And a wheel stand could be very high , or very little with spin. So the initial thoughts are outside of the bellhousing ....leaning towards , am I changing the cars characteristics at launch because of how the engines power band comes into play ( way over peak torque ) or right at peak torque. It is likely the clutch CW has some input here.....BUT which has the greater influence?

[Mike Pearson]

Back years ago when I ran a stick in my car. The car was faster launching at high RPM. this was before all of the good clutch stuff and rev limiters we have now. I would leave at 9000 RPM and pull the shifter to second as quickly as possible. Then shift the remaining gears at 8000. The car liked a light flywheel 13 lb. Clutch was 1800 base as I remember with a six pad disc. Dead hook. I had 2 transmissions one 305 low and one with a 3.19 low. SS/I and SS/J. It was brutal on parts.

[weedburner]

Originally Posted by joespanova

Using my own as an example , with no change in the bell housing and enough base ( because I don't use a data logger ) to launch the car well enough to keep me near or well into decent 60 fts. I can apparently spin or wheel stand just by varying launch RPM. And a wheel stand could be very high , or very little with spin. So the initial thoughts are outside of the bellhousing ....leaning towards , am I changing the cars characteristics at launch because of how the engines power band comes into play ( way over peak torque ) or right at peak torque. It is likely the clutch CW has some input here.....BUT which has the greater influence?

Because you have centrifugal adding clamp pressure with rpm, the higher you launch the harder the clutch hits.

When you are launching way over the engine's peak torque, the clutch hits harder and your engine is likely initially losing rpm during launch. That loss of engine rpm adds torque to the transmission's input shaft. That extra torque due to stored energy exiting the engine's rotating assy, along with a harder hitting clutch, causes excessive wheelspin before the car gets a chance to transfer weight.

When you are launching from a lower rpm closer to your engine's torque peak, the clutch slips more and the engine may or may not lose rpm. If it doesn't lose rpm, the input shaft will only see engine torque during launch. If you launch below the engine's torque peak, the engine will gain rpm during launch. In that case the engine's rotating assy will absorb some of the engine's torque, which will in-turn reduce the torque that the input shaft sees.

Note on the graph below that this 425ftlb engine puts out way more than 425ftlbs when it is losing rpm, and much less than 425ftlbs when it is gaining rpm. That's due to the engine's rotating assy releasing and absorbing energy as it loses or gains rpm...



Here's those calculated input shaft torque numbers multiplied by the transmission ratios to show driveshaft torque...



If you are wondering how accurate those calculated torque numbers might be, here's those calculated driveshaft torque numbers compared to the actual AccelG trace from that pass...

[weedburner]

Originally Posted by joespanova

Using my own as an example , with no change in the bell housing and enough base ( because I don't use a data logger ) to launch the car well enough to keep me near or well into decent 60 fts. I can apparently spin or wheel stand just by varying launch RPM. And a wheel stand could be very high , or very little with spin. So the initial thoughts are outside of the bellhousing ....leaning towards , am I changing the cars characteristics at launch because of how the engines power band comes into play ( way over peak torque ) or right at peak torque. It is likely the clutch CW has some input here.....BUT which has the greater influence?

Because you have centrifugal adding clamp pressure with rpm, the higher you launch the harder the clutch hits.

When you are launching way over the engine's peak torque, the clutch hits harder and your engine is likely initially losing rpm during launch. That loss of engine rpm adds torque to the transmission's input shaft. That extra torque due to stored energy exiting the engine's rotating assy, along with a harder hitting clutch, causes excessive wheelspin before the car gets a chance to transfer weight.

When you are launching from a lower rpm closer to your engine's torque peak, the clutch slips more and the engine may or may not lose rpm. If it doesn't lose rpm, the input shaft will only see engine torque during launch. If you launch below the engine's torque peak, the engine will gain rpm during launch. In that case the engine's rotating assy will absorb some of the engine's torque, which will in-turn reduce the torque that the input shaft sees.

Note on the graph below that this 425ftlb engine puts out way more than 425ftlbs when it is losing rpm, and much less than 425ftlbs when it is gaining rpm. That's due to the engine's rotating assy releasing and absorbing energy as it loses or gains rpm...



Here's those calculated input shaft torque numbers multiplied by the transmission ratios to show driveshaft torque...



If you are wondering how accurate those calculated torque numbers might be, here's those calculated driveshaft torque numbers compared to the actual AccelG trace from that pass...

[joespanova]

Weedburner , that's good stuff and my take away ( and what I'd been realizing lately ) is that I've been launching with too much RPM. I'd just figured I needed that engine speed but now realize I've missed the target all along....which will have me drop from , say 7000 or so to 6000 or so...this is a 393 SBC ( n/a ).

[weedburner]

If you are looking for your best ET, more launch rpm is better as you will have more stored energy available to get the car moving. Problem is the traditional model of adjustable static+CW clutch tuning won't get you there,

Don't confuse more launch rpm with a heavier flywheel as they are not the same with regards to storing energy prior to the start. While a heavier flywheel/clutch will also make more stored energy available for launch, the problem with a heavier flywheel is that the energy you draw from it during launch then has to be paid back before you cross the stripe. The car can launch harder with more stored energy available, but it will then accelerate slower as the rpm's climb back up. Gain some here, lose some there, it basically balances out when the outflow of stored energy is efficient. The problem you see with a heavier flywheel is that it increases the percentage of stored energy that is lost when the tires spin. That is the basic reason drag racers see benefits when switching to lighter clutch/flywheels, an overall reduction of stored energy means less stored energy ends up wasted during wheelspeed spikes after the shifts.

It might help to think of the engine's rotating assy as a torque storage device similar to a battery. You lose engine torque output as you charge it up with rpm, then gain engine torque output as you draw rpm out of it. When you cross the stripe, the engine's rotating assy will be fully charged with rpm. Sure there will be give and take as the engine loses and regains rpm as the car works its way thru the gears, but those gains and losses basically cancel each other out. The thing to look at is the net difference between engine rpm on the starting line vs engine rpm crossing the finish line.

...If the rpm on the starting line is the same as crossing the finish line, then all the engine's torque production made it to the transmission's input shaft to accelerate the car. Start with a full battery, end with a full battery.
...If the rpm on the starting line is lower vs crossing the finish line, that's like starting out with less than a fully charged battery. Some of the engine's overall net torque production gets absorbed charging its rotating assy, reducing the overall net torque available to accelerate the car between the start/finish lines.
...If the rpm on the starting line is higher vs crossing the finish line, then that extra start rpm becomes energy available for launch that doesn't have to be paid back before crossing the stripe. You end up with more torque available to accelerate the car between the start and finish lines than the engine actually produced.

The key to taking advantage of high rpm starts is the ability to control the stored energy discharge rate, which is in-turn controlled by how fast the clutch pulls the engine down against WOT. For that you need a 2-stage clutch. A 1st stage that maximizes efficiency during high rpm launch, then a 2nd stage rate that maximizes efficiency after the shifts.

[James Hensler]

Originally Posted by weedburner

If you are looking for your best ET, more launch rpm is better as you will have more stored energy available to get the car moving. Problem is the traditional model of adjustable static+CW clutch tuning won't get you there,

Don't confuse more launch rpm with a heavier flywheel as they are not the same with regards to storing energy prior to the start. While a heavier flywheel/clutch will also make more stored energy available for launch, the problem with a heavier flywheel is that the energy you draw from it during launch then has to be paid back before you cross the stripe. The car can launch harder with more stored energy available, but it will then accelerate slower as the rpm's climb back up. Gain some here, lose some there, it basically balances out when the outflow of stored energy is efficient. The problem you see with a heavier flywheel is that it increases the percentage of stored energy that is lost when the tires spin. That is the basic reason drag racers see benefits when switching to lighter clutch/flywheels, an overall reduction of stored energy means less stored energy ends up wasted during wheelspeed spikes after the shifts.

It might help to think of the engine's rotating assy as a torque storage device similar to a battery. You lose engine torque output as you charge it up with rpm, then gain engine torque output as you draw rpm out of it. When you cross the stripe, the engine's rotating assy will be fully charged with rpm. Sure there will be give and take as the engine loses and regains rpm as the car works its way thru the gears, but those gains and losses basically cancel each other out. The thing to look at is the net difference between engine rpm on the starting line vs engine rpm crossing the finish line.

...If the rpm on the starting line is the same as crossing the finish line, then all the engine's torque production made it to the transmission's input shaft to accelerate the car. Start with a full battery, end with a full battery.
...If the rpm on the starting line is lower vs crossing the finish line, that's like starting out with less than a fully charged battery. Some of the engine's overall net torque production gets absorbed charging its rotating assy, reducing the overall net torque available to accelerate the car between the start/finish lines.
...If the rpm on the starting line is higher vs crossing the finish line, then that extra start rpm becomes energy available for launch that doesn't have to be paid back before crossing the stripe. You end up with more torque available to accelerate the car between the start and finish lines than the engine actually produced.

The key to taking advantage of high rpm starts is the ability to control the stored energy discharge rate, which is in-turn controlled by how fast the clutch pulls the engine down against WOT. For that you need a 2-stage clutch. A 1st stage that maximizes efficiency during high rpm launch, then a 2nd stage rate that maximizes efficiency after the shifts.

Hemi cars cross the stripe at over 9500 so you want us to launch there! Lmao no clue

[weedburner]

Originally Posted by James Hensler

Hemi cars cross the stripe at over 9500 so you want us to launch there! Lmao no clue

So what is it that keeps you from launching from 9500 or above?

[Stan Weiss]

Originally Posted by weedburner

If you are looking for your best ET, more launch rpm is better as you will have more stored energy available to get the car moving. Problem is the traditional model of adjustable static+CW clutch tuning won't get you there,

Don't confuse more launch rpm with a heavier flywheel as they are not the same with regards to storing energy prior to the start. While a heavier flywheel/clutch will also make more stored energy available for launch, the problem with a heavier flywheel is that the energy you draw from it during launch then has to be paid back before you cross the stripe. The car can launch harder with more stored energy available, but it will then accelerate slower as the rpm's climb back up. Gain some here, lose some there, it basically balances out when the outflow of stored energy is efficient. The problem you see with a heavier flywheel is that it increases the percentage of stored energy that is lost when the tires spin. That is the basic reason drag racers see benefits when switching to lighter clutch/flywheels, an overall reduction of stored energy means less stored energy ends up wasted during wheelspeed spikes after the shifts.

It might help to think of the engine's rotating assy as a torque storage device similar to a battery. You lose engine torque output as you charge it up with rpm, then gain engine torque output as you draw rpm out of it. When you cross the stripe, the engine's rotating assy will be fully charged with rpm. Sure there will be give and take as the engine loses and regains rpm as the car works its way thru the gears, but those gains and losses basically cancel each other out. The thing to look at is the net difference between engine rpm on the starting line vs engine rpm crossing the finish line.

...If the rpm on the starting line is the same as crossing the finish line, then all the engine's torque production made it to the transmission's input shaft to accelerate the car. Start with a full battery, end with a full battery.
...If the rpm on the starting line is lower vs crossing the finish line, that's like starting out with less than a fully charged battery. Some of the engine's overall net torque production gets absorbed charging its rotating assy, reducing the overall net torque available to accelerate the car between the start/finish lines.
...If the rpm on the starting line is higher vs crossing the finish line, then that extra start rpm becomes energy available for launch that doesn't have to be paid back before crossing the stripe. You end up with more torque available to accelerate the car between the start and finish lines than the engine actually produced.

The key to taking advantage of high rpm starts is the ability to control the stored energy discharge rate, which is in-turn controlled by how fast the clutch pulls the engine down against WOT. For that you need a 2-stage clutch. A 1st stage that maximizes efficiency during high rpm launch, then a 2nd stage rate that maximizes efficiency after the shifts.

There is another case where the car is geared for the best 60' time and et which has it on the rev limiter before the finish line.


Stan