2017 Mazda MX-5 Miata RF Vs. 2017 Toyota 86

[Tave]

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They aren't running +.5 seconds faster than everyone else by "mashing" the throttle the best. They are torque braking it to induce wheelspin and then repeating the procedure at different rpms to find the optimum sweetspot between getting off the line quickly and being in the meat of the powerband when the tires hook up. No, they don't want excessive spin, but they want a little.

[MX793]

Launch control is not brake torquing though. There, they are treating the torque converter sorta like a clutch (letting it stall high during the launch) and then modulating in a bit of wheel spin/TC, and then of course not cutting the throttle at the release of the brake.

What exactly do you think brake torquing is? 

When you brake torque, you hold the brake down with your left foot to keep the car stationary while applying throttle to build revs before releasing the brake and launching.  Launch revs will either be limited by what the driver wants or the stall speed of the torque converter, whichever is lower.

In the 8AT Vette or F-Type, launch control works by the driver holding the brake with their left foot and flooring the throttle with their right.  The ECM puts the RPMs to the programmed level (~2K for those cars) and then the driver releases the brake when ready to go (the Vette also does a little chime to let the driver know the system is ready).  It's the exact same thing as brake torquing.  It just has more computer control in place to optimize traction management and the car sets the launch RPM vs the driver needing to modulate the throttle on a non-LC equipped auto (or settle for the converter stall speed as the launch RPM).

[CaminoRacer]

The presence of special traction settings for launch control means that it's not quite the same as old school brake torquing.

[Laconian]

The presence of special traction settings for launch control means that it's not quite the same as old school brake torquing.

That probably adjusts the hysteresis thresholds. Traction control usually backs WAY off when slippage occurs; I'm guessing launch control reduces the severity of the intervention.

[2o6]

this has gone on for four pages....

[CaminoRacer]

That probably adjusts the hysteresis thresholds. Traction control usually backs WAY off when slippage occurs; I'm guessing launch control reduces the severity of the intervention.

Exactly

[Soup DeVille]

Gotta hand it to you guys; I haven't seen bench racing this involve since the glory days of C/D

[Soup DeVille]

That probably adjusts the hysteresis thresholds. Traction control usually backs WAY off when slippage occurs; I'm guessing launch control reduces the severity of the intervention.

The term used in the industry is the mu rate.

[MX793]

The presence of special traction settings for launch control means that it's not quite the same as old school brake torquing.

Brake torquing (the act of holding the brake while "winding up" the drivetrain by spinning up the engine/torque converter) is part of what the launch control does.  The traction management once the brake is released and the car starts moving (which would be up to the driver in an old-school car) is the other part of it.

In general, automatic transmissions are known as being more useful for lazy commuters than for hardcore racers. But it may be surprising for some to know that many pro drag-racing cars have heavy-duty auto gearboxes. That's because the brake-torque launch is an automatic specialty. This launch involves keeping the car stationary by flooring the brakes with the left foot, while using the right foot to rev up the engine against the torque converter. In technical terms, this preloads the entire drivetrain with the stress of a launch, allowing the engine to rev closer to its power and torque peaks at the starting line.

http://www.modernracer.com/tips/dragracinglaunchtechniques.html

Whether it's entirely done by a human or semi/fully automated by a computer (launch control), it's still brake torquing.

[Laconian]

The term used in the industry is the mu rate.

Thanks!

[GoCougs]

They completely disengage the output shaft from the torque converter? That sounds... dubious/not useful.

No, it's always engaged. The torque converter can be allowed to slip (usually at idle and low RPM) or lock up (higher RPM).

[GoCougs]

The presence of special traction settings for launch control means that it's not quite the same as old school brake torquing.

Traction settings, throttle modulation, and maybe something with the torque converter lock up.

I mean, if you have to select it from a menu, it's not brake torquing which is my point.

And I reiterate, plenty of cars are faster with NOT brake torquing, and the G is infamously one of them (the 'SPIN is more than welcome to Google the myriad G37 fanboy boards).

[AutobahnSHO]

Third, torque braking is no more strain on the engine, transmission and drive train and car in general than hard acceleration (provided a wheel isn't spinning). The engine just spins against a slipping torque converter.

Lol tell that to my parents who had to replace the torque converter when my brothers were messing around.

[MX793]

Lol tell that to my parents who had to replace the torque converter when my brothers were messing around.

Yeah, you can overheat the transmission fluid (lots of fluid shear), which will cause it to break down.

[GoCougs]

You can't overheat a torque converter (it's just metal and a few bearings) and "lots of fluid" shear" is the principal under which it transmits torque.

[MX793]

You can't overheat a torque converter (it's just metal and a few bearings) and "lots of fluid" shear" is the principal under which it transmits torque.

You get more relative shear while brake torquing than normal driving.  The impeller is spinning at a couple thousand RPM while the turbine and stator are stationary.  That induces a lot of fluid friction and will overheat the fluid eventually.  How quickly depends on how much fluid is in the system, what kind of auxiliary cooling there is, and the design of the converter.  Brake torquing can overheat the transmission fluid the same way overworking the transmission can (i.e. pulling too heavy a load up a long, steep grade with your foot to the floor or sustained hard lapping on a track).  It'll overheat quicker than in a driving scenario because when you're standing still, you don't have as much air blowing over the trans cooler.

[GoCougs]

Tave was incorrect - brake torquing does not harm the transmission and in total is no more a strain on any part of the vehicle; including transmission overheating; than moderate or full throttle driving.

[AutobahnSHO]

Yeah, ok. When a teenage boy has his foot firmly on the brake and the other teenage boy mashes the gas and neither lets go, the torque converter in a gen2 Taurus doesn't even last 90seconds.

[MX793]

Yeah, ok. When a teenage boy has his foot firmly on the brake and the other teenage boy mashes the gas and neither lets go, the torque converter in a gen2 Taurus doesn't even last 90seconds.

You're wrong.  It's impossible for trans fluid in a torque converter to overheat.  In fact, those "transmission cooler" heat exchangers that every AT car comes fitted with are just snake oil.  You can remove them and save some weight with no negative effects.  And the heavy duty transmission coolers they try to upsell you on with truck towing packages are a total money grab.

[Soup DeVille]

Tave was incorrect - brake torquing does not harm the transmission and in total is no more a strain on any part of the vehicle; including transmission overheating; than moderate or full throttle driving.

So when the engine is operating at WOT, the transmission is engaged, and the car isn't moving: where does that extra energy go?

[GoCougs]

You're wrong.  It's impossible for trans fluid in a torque converter to overheat.  In fact, those "transmission cooler" heat exchangers that every AT car comes fitted with are just snake oil.  You can remove them and save some weight with no negative effects.  And the heavy duty transmission coolers they try to upsell you on with truck towing packages are a total money grab.

Trans fluid can't overheat in a torque converter. The trans fluid in a torque converter is the same fluid in the whole of the transmission - it circulates throughout courtesy of pumps (one in the torque converter and one in the transmission body) - so the trans fluid overheats, period, and not in any specific area within the transmission, and you're not overheating trans fluid in 90 seconds.

[2o6]

these threads are what keep CarSPIN alive

[GoCougs]

So when the engine is operating at WOT, the transmission is engaged, and the car isn't moving: where does that extra energy go?

Uhhhh...

The "extra energy" (actually power which is energy/time) transferred through the torque converter is the same whether the vehicle is stationary or moving.

[MX793]

Uhhhh...

The "extra energy" (actually power which is energy/time) transferred through the torque converter is the same whether the vehicle is stationary or moving.

Uhh, you feeling all right, buddy?  Your grasp of basic thermodynamics seems to be slipping.  When you aren't brake torquing, the energy into the impeller goes into moving the turbine (kinetic energy -> kinetic energy).  Losses due to fluid slip/shear manifest as heat.  If you are holding the car (and turbine) stationary and spinning up the torque converter, practically all of that kinetic energy out of the impeller goes to just stirring up the fluid, which generates a lot of heat.

[Soup DeVille]

Uhhhh...

The "extra energy" (actually power which is energy/time) transferred through the torque converter is the same whether the vehicle is stationary or moving.

You feeling ok man, or does brake torquing happen in some sort of timeless way?

[MX793]

Trans fluid can't overheat in a torque converter. The trans fluid in a torque converter is the same fluid in the whole of the transmission - it circulates throughout courtesy of pumps (one in the torque converter and one in the transmission body) - so the trans fluid overheats, period, and not in any specific area within the transmission, and you're not overheating trans fluid in 90 seconds.

Sure it can.  That's where the energy is being imparted through, and that's where all of the energy conversion takes place.

Fact:  A/Ts generate more heat than M/Ts and are more susceptible to overheating.
Fact:  All production cars with torque converter A/Ts have dedicated, remotely mounted trans fluid coolers
Fact:  No production M/T cars have remotely mounted trans oil/fluid coolers

What's the difference?  One has a torque converter and the other doesn't.  And before you raise the point that A/Ts use planetary gearsets and M/Ts don't and that somehow generates way more heat, the Toyota Synergy Hybrid Drive system also uses planetary gearsets, doesn't have a torque converter, and doesn't pump its trans oil/fluid through a remotely mounted cooler.  So all that extra heat in an A/T isn't coming from the gears, it's predominantly coming from the torque converter.

[GoCougs]

Why you guys consistently follow these rabbit holes to this extent just amazes me. In summary, Tave is wrong, as is anyone who agreed with him:

1. Brake torquing an AT is not harmful to the AT or the car.
2. You will not overheat an AT by brake torquing.

Brake torquing is no more harmful to the AT or car itself than moderate or full throttle driving, and there are no arguments to the contrary.

[MX793]

Why you guys consistently follow these rabbit holes to this extent just amazes me. In summary, Tave is wrong, as is anyone who agreed with him:

1. Brake torquing an AT is not harmful to the AT or the car.
2. You will not overheat an AT by brake torquing.

Brake torquing is no more harmful to the AT or car itself than moderate or full throttle driving, and there are no arguments to the contrary.

You can call a goose a duck all you want, but it doesn't make you any more correct.  Your argument that a torque converter doesn't generate heat outright defies physics and you've yet to provide any explanation other than "I'm right and you're wrong" to back up that assertion.  Take the L and move on, bro.

Just for fun, here's a thread of Corvette guys sharing stories of destroying their torque converters at the drag strip.
https://www.corvetteforum.com/forums/c3-tech-performance/197978-anyone-ever-blow-out-a-torque-converter.html

[12,000 RPM]

Cougs ITT:

[GoCougs]

You can call a goose a duck all you want, but it doesn't make you any more correct.  Your argument that a torque converter doesn't generate heat outright defies physics and you've yet to provide any explanation other than "I'm right and you're wrong" to back up that assertion.  Take the L and move on, bro.

You latched onto a strawman and let it drag you down a rabbit hole into an L. I said nothing about heat.

ALL transmission types - whether AT, DSG, SMG or M/T - generate - torque converters, clutches, bands, gears, pumps, bearings, seals, etc. are ALL are sources of inefficiency.

Any transmission designed today is designed to dissipate heat, ergo, only under extreme circumstances can they overheat.

Tave is wrong, as is anyone who agreed with him, and thusly I repeat for posterity:

1. Brake torquing an AT is not harmful to the AT or the car.
2. You will not overheat an AT by brake torquing.

Brake torquing is no more harmful to the AT or car itself than moderate or full throttle driving, and there are no arguments to the contrary.