Practical Transmission Tuning: Torque Convertor & Flex Plate

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Torque Convertor & Flex Plate

06.50

00:00	In this section of the course, we're going to be discussing transmission upgrade options.
00:04	When it comes to most drivetrain parts, if we're significantly increasing torque output, we may exceed limits.
00:11	If a component won't be up to the task, the logical solution is to install a more capable component.
00:18	Let's start at the front of the system by looking at our options for upgrading the torque converter and flex plate.
00:24	When significantly increasing engine output or operating a vehicle in a heavy towing, off-road, or race condition, a more durable than stock stamped housing unit or a billet housing torque converter may be required.
00:39	Reinforced housings reduce converter deflection as rotational speed, fluid pressure, and torque input vary.
00:47	The flexibility in the torque converter and flex plate that we discussed in the previous section of the course, which are by design and acceptable in moderation, can become a liability when additional pressure, force, and rotational speed are applied.
01:02	At a certain point, we need to restrict distortion with more robustly constructed parts to avoid the converter deforming or the flex plate flexing to the point the converter can make unwanted metal-to-metal contact with the transmission housing.
01:17	Beyond reducing flex, we also simply want to strengthen these items, so they don't break when highly stressed.
01:24	In addition to that strength, billet converters have the added advantage of serviceability as well.
01:30	If we have a welded stamped steel converter and we wear it out or want to change converter behavior, generally we'll be sending it out for a rebuild or purchasing a new unit entirely.
01:42	With a billet converter, internal components are more easily accessed since the cover simply comes apart with bolts at which point we can inspect or swap out internals or change stall speed to optimize for changing race conditions or driver preference.
01:58	Now, on to some terms you've likely heard people use to describe a torque converter's characteristics.
02:03	Loose, tight, and slip.
02:07	Generally, when someone says they switch to a looser torque converter, they mean it has a higher stall speed than what they used previously.
02:15	What they're saying is the torque converter is set up to allow the impeller to outpace the turbine more significantly before the fluid coupling effect transfers enough energy into the turbine to cause forward motion.
02:29	The greater the slip, which refers to the speed differential between the impeller and turbine, the greater the percentage of total energy is converted into heat instead of forward motion.
02:40	That doesn't sound ideal, but the good news is vehicle acceleration response can actually still improve if this slip keeps the engine operating at a higher RPM where it makes more horsepower and torque.
02:55	So, how is that possible? Let's run through an example to help clear things up.
03:01	At 1500 RPM, let's say we have a tight torque converter and the torque converter clutch is also locked up.
03:08	So, we're getting efficient transfer of energy, but perhaps the engine only makes 150 foot-pounds of torque at 1500 RPM.
03:18	Now, let's say we have the torque converter clutch unlocked, a looser converter installed, and the engine can flare up to 4000 RPM where it makes 400 foot-pounds of torque.
03:28	Even if we're losing a significant portion of that 400 foot-pounds of torque to heat, we're still getting a lot more than 150 foot-pounds of torque to the tires.
03:39	Put simply, even only 50% of a big number can be greater than 100% of a small amount, and keeping the engine operating in a range where it makes high output is vital in high performance applications.
03:52	Tighter converters allow for less slip without torque converter clutch lockup, providing a more direct feel and increased efficiency in terms of the percentage of engine torque transferred to the transmission.
04:06	This is generally what we want in a street vehicle, because it's more predictable in low to medium throttle situations, feels more direct, and is more efficient.
04:16	When purchasing a converter, if we're working with a common vehicle application that's mildly modified and we only want a mild increase in stall speed to help get off the line better, chances are we can pick something off the shelf and have a good result.
04:31	Some vendors may even say this converter has a stall speed 300 RPM higher than stock to help make the buying decision easier.
04:39	Just remember, many factors go into actual stall speed at any given moment.
04:45	A converter listed as being a 2000 RPM stall converter may not stall at 2000 RPM in your particular application.
04:55	When selecting an aftermarket torque converter, if we want to give ourselves a greater chance of selecting the ideal unit on the first try, and especially if we're working with a vehicle that's quite modified or will be used for racing, we may want to work with an experienced supplier that's willing to have a discussion and tailor the unit to our application.
05:16	Lastly, like the rest of the torque converter, the torque converter clutch portion needs to be upgraded if the stock component can't handle the amount of torque we'll be making.
05:26	That covers just about everything you need to know when it comes to torque converters and flex plate upgrades.
05:32	So, let's do a quick recap before moving on.
05:36	Upgrading the torque converter and flex plate is often necessary for significant engine output increases, as well as heavy towing, off-road, or race conditions.
05:49	Upgrading to a more durable converter housing reduces deflection and stabilizes it at higher rotational speeds, higher fluid pressures, and torque levels.
06:01	Flexibility in these components, while acceptable in moderation, becomes problematic if pushed too far by a significant engine torque increase.
06:10	This requires more robust construction to prevent deformation and unwanted metal contact.
06:16	Billet converters offer strength and serviceability, allowing easier access to internals for inspection, modifications, and stall behavior adjustments.
06:27	Loose and tight converters refer to stall speed characteristics, impacting energy transfer efficiency and vehicle acceleration response.
06:37	Balancing these factors is essential when selecting an aftermarket torque converter, particularly for multi-purpose vehicles and race applications.