I'm posting this because someone required more information, and I felt it should be in a different thread.
As probably you know, the Toyota 340 series of transmissions are generally very well made and demonstrate excellent durability in unmodified applications. The framework is present for an extremely strong transmission that is to be used for a performance application.
The problem is that the original calibration is engineered for driver comfort rather than ultimate strength. The soft, sliding shifts that are part of the original design are not appropriate for increased horsepower applications, towing, off road, racing, etc. These calibration inadequacies quickly manifest themselves as extremely poor shift quality, and more often than not, severe damage to the gear box is soon to follow.
Without going into too much technical detail, the factory shortcomings can be addressed through modification and recalibration of the control valve assembly, a.k.a. the valve body.
The valve body is a component that is comprised of valves, solenoids, an orifice plate and an intricate series of passages- it is the most complex part of the most complex part of a vehicle- the automatic transmission.
The function of the valve body is to act as the "brain" of the automatic transmission- it directs hydraulic pressure to the appropriate clutches and bands at the right time to initiate upshifts, down shifts, reverse, converter clutch application, etc. As well as controlling shift timing and shift quality, it is also responsible for directing hydraulic pressure to the cooler and the lubrication circuit.
As you can imagine, the transmission's operation can be drastically altered and also customized to the application through modifications to this component. We have been working with these transmissions for many years. Most of our development work has been done on the Toyota Supra, which uses a slightly different configuration of this same transmission. Our modified 340 transmissions are out there handling up to about 700 horsepower and the main reason that this is possible is because of the modifications to the valve body that we have developed.
When someone with a 4Runner had found us through the Supra community, we began working on modifications that were more appropriate for Toyota trucks- especially those that were needing to handle the additional power that accompanies the installation of a supercharger. The results were very favorable and we have become the main source of modified valve bodies among 4Runner and Tacoma owners.
At the risk of oversimplification, there are a few things that are done in concert to create much more favorable operation of the gearbox.
The first thing that needs to be done is to increase the hydraulic operating pressure of the transmission- this pressure is known as "line pressure". All hydraulic functions of the trans are based on this pressure- what is especially of concern, for these purposes, is the clamping force which is applied to the clutches and bands to get them to hold against engine torque. In simple terms, increased engine output is complemented by increased line pressure and increased "clamp" on the clutches- this can be likened to a performance clutch with a heavier spring in a manual transmission equipped vehicle.
The idea is to raise this pressure only slightly at light throttle but increase it by 30-40% at full throttle where it is needed. The effect of this is shifts that are not overly uncomfortable at lower throttle openings, but at heavy throttle, we can accomplish firm shifts with short clutch application time and increased clamping force.
An additional benefit of this is increased flow through the transmission cooler and lube system.
Secondly, hydraulic pressure is normally routed through an orifice in a metal "separator plate" that resides between the two halves of the valve body before it gets to its intended destination. By altering these orifices, we can increase the volume of hydraulic oil that is used to apply the various clutches and bands. This is where some customizing can be done for the given application, and to some degree, to customer preference.
The final part of modification is the alteration of the accumulator circuits. These are hydraulic circuits that are parallel to the components that are used for upshifting. Their function is to absorb or "accumulate" some of the hydraulic pressure that is intended to apply a clutch pack. By limiting the action of what is essentially a "shock absorber" for each upshift, we are able to further reduce clutch lock up time and shift lag at wide open throttle.
The end result is that shift time is reduced by 30 to 80%, depending on the customers preference regarding the amount of acceptable shift feel. The clamping force that is required to apply the clutches and bands is increased by 30 to 40% at full throttle. Flow through the cooler and lube circuit is increased and the converter clutch application time is also reduced.
As probably you know, the Toyota 340 series of transmissions are generally very well made and demonstrate excellent durability in unmodified applications. The framework is present for an extremely strong transmission that is to be used for a performance application.
The problem is that the original calibration is engineered for driver comfort rather than ultimate strength. The soft, sliding shifts that are part of the original design are not appropriate for increased horsepower applications, towing, off road, racing, etc. These calibration inadequacies quickly manifest themselves as extremely poor shift quality, and more often than not, severe damage to the gear box is soon to follow.
Without going into too much technical detail, the factory shortcomings can be addressed through modification and recalibration of the control valve assembly, a.k.a. the valve body.
The valve body is a component that is comprised of valves, solenoids, an orifice plate and an intricate series of passages- it is the most complex part of the most complex part of a vehicle- the automatic transmission.
The function of the valve body is to act as the "brain" of the automatic transmission- it directs hydraulic pressure to the appropriate clutches and bands at the right time to initiate upshifts, down shifts, reverse, converter clutch application, etc. As well as controlling shift timing and shift quality, it is also responsible for directing hydraulic pressure to the cooler and the lubrication circuit.
As you can imagine, the transmission's operation can be drastically altered and also customized to the application through modifications to this component. We have been working with these transmissions for many years. Most of our development work has been done on the Toyota Supra, which uses a slightly different configuration of this same transmission. Our modified 340 transmissions are out there handling up to about 700 horsepower and the main reason that this is possible is because of the modifications to the valve body that we have developed.
When someone with a 4Runner had found us through the Supra community, we began working on modifications that were more appropriate for Toyota trucks- especially those that were needing to handle the additional power that accompanies the installation of a supercharger. The results were very favorable and we have become the main source of modified valve bodies among 4Runner and Tacoma owners.
At the risk of oversimplification, there are a few things that are done in concert to create much more favorable operation of the gearbox.
The first thing that needs to be done is to increase the hydraulic operating pressure of the transmission- this pressure is known as "line pressure". All hydraulic functions of the trans are based on this pressure- what is especially of concern, for these purposes, is the clamping force which is applied to the clutches and bands to get them to hold against engine torque. In simple terms, increased engine output is complemented by increased line pressure and increased "clamp" on the clutches- this can be likened to a performance clutch with a heavier spring in a manual transmission equipped vehicle.
The idea is to raise this pressure only slightly at light throttle but increase it by 30-40% at full throttle where it is needed. The effect of this is shifts that are not overly uncomfortable at lower throttle openings, but at heavy throttle, we can accomplish firm shifts with short clutch application time and increased clamping force.
An additional benefit of this is increased flow through the transmission cooler and lube system.
Secondly, hydraulic pressure is normally routed through an orifice in a metal "separator plate" that resides between the two halves of the valve body before it gets to its intended destination. By altering these orifices, we can increase the volume of hydraulic oil that is used to apply the various clutches and bands. This is where some customizing can be done for the given application, and to some degree, to customer preference.
The final part of modification is the alteration of the accumulator circuits. These are hydraulic circuits that are parallel to the components that are used for upshifting. Their function is to absorb or "accumulate" some of the hydraulic pressure that is intended to apply a clutch pack. By limiting the action of what is essentially a "shock absorber" for each upshift, we are able to further reduce clutch lock up time and shift lag at wide open throttle.
The end result is that shift time is reduced by 30 to 80%, depending on the customers preference regarding the amount of acceptable shift feel. The clamping force that is required to apply the clutches and bands is increased by 30 to 40% at full throttle. Flow through the cooler and lube circuit is increased and the converter clutch application time is also reduced.
