It’s the little things in life which seem to make all the difference. If you are considering an electronically controlled automatic transmission for your carbureted muscle car, these transmissions demand an accurate throttle position sensor (TPS) reading. This device converts throttle movement into voltage that can be easily monitored by the transmission as throttle position. All this sounds simple – until you have to adapt one to an existing Edelbrock, Rochester Q-jet, or Holley carburetor. Then things can get complicated and sloppy. But we’ve found several elegant solutions.
Mike Hoy runs a company called HGM Automotive Electronics. He builds the really successful Compu-Shift automatic trans controller for the GM 4L60E and 4L80E families of electronic transmissions as well as several other Ford, Toyota, and even a Chrysler trans or two. All of these electronic transmissions require input from a TPS. This is a simple connection when the engine is controlled by some form of EFI, since digital fuel control also requires a throttle position sensor (TPS) input.
A TPS sensor merely converts the rotational movement of the throttle blades into a 0 to 5-volt scale reading. This is a critical input since this is how electronic transmissions determine load. With a closed or only partially open throttle, the voltage signal is low – around 1.0 to 2.0 volts. Then as the throttle opens, the voltage increases to a maximum of 4.9 to 5.0 volts which represents wide-open-throttle (WOT). The transmission uses these inputs to vary the hydraulic line pressure. With higher TPS readings, the valve body increases the line pressure to apply more force to the clutches and bands to reduce slippage under high load.
For carbureted cars, the requirement for a TPS signal becomes a bit more complicated. Several companies offer cable-style conversions where a GM 700-R4 style cable is connected to a remote-mount for a TPS sensor. While these conversions certainly work, they can be clunky, often subject to less than reliable operation, and frankly they contribute to a cluttered engine compartment. Hoy’s idea was to create what he calls the Accu-Link.
This is a simple, stainless steel conversion kit which mounts the very popular GM three-pin Weatherpak TPS sensor directly on the side of the carburetor with an adjustable linkage. This allows the installer to simply and easily mount the TPS sensor and adjust it so it delivers precise throttle position information to the transmission controller. This may not sound like a big deal, but without accurate TPS information, the electronic controller will find it difficult to properly control the transmission.
The Accu-Link is designed to fit all the popular Holley, Carter, Edelbrock, and even the Rochester Q-jet carburetors. The installation isn’t difficult but does require careful installation to ensure that it will work consistently. This involves ensuring the linkage does not bind or kink and that the sensor is properly adjusted. Unlike many aftermarket pieces where instructions are either non-existent or appear to be an afterthought, the Accu-Link instructions are clear, concise, and photographed to ensure proper installation. Once the Accu-Link is installed, the system works very well and looks great doing it.
We actually installed one of these kits on our small-block El Camino after bolting in a performance-built 4L60E transmission controlled by HGM’s Compu-Shift transmission controller. As an aside, HGM recently updated the Compu-Shift to the Sport or Pro models which use free software so now all transmission control aspects can be adjusted and monitored with your phone. We’ve worked with this new system. Not only does it work as advertised, but this upgraded Compu-Shift version is less expensive, since it no longer requires the large, hand-held controller with its push-button controls and digital readout.
On a similar TPS note, a new company called Fuel Systems Technology (FST) has created a new line of Holley-based carburetors. This is notable here because FST offers a TPS sensor for certain model carburetors as an option starting with the RTX model carburetors. The TPS sensor mounts directly to the throttle base plate and operates directly off the primary throttle shaft so there’s no lost motion due to linkage deflection.
If you already have a Holley carburetor, Holley also offers a TPS conversion kit. It is designed to only work in conjunction with 4150/4160 style Holley carburetors fitted with an electric choke. We converted a 600 cfm Holley carb using this kit. It works very well and is similarly priced.
Innovate Motorsports also offers a slick, direct-mounting TPS sensor-mounting kit complete with the GM Weatherpak three-pin sensor. The Innovate kit is designed only for 4150 style Holley carbs that do not use a choke mount on the passenger side of the carburetor. The kit uses the primary throttle shaft to directly act on the TPS sensor so there’s no linkage motion to affect the TPS accuracy. Plus, the Innovate kit includes resistors to drop the typical 12 to 14-volt system voltage down to the 5-volt scale needed. This is especially useful if you are using this sensor for data logging.
As an example of the benefit of a TPS conversion, consider data logging air/fuel ratio along with throttle position and RPM. Innovate Motorsports offers several ways to data log all this information. It can be displayed on either an electronic strip chart or virtual gauges on your laptop where you can look at the air/fuel ratio (AFR), throttle position, and RPM all at the same time. On a road or autocross course, this could be very valuable information. As an example, you can easily pick out the AFR at half-throttle as a tuning aid.
Another application for this TPS sensor is to use it as an accurate trigger-point for a nitrous system instead of a simple micro-switch. As an example, the TPS signal could be used to trigger a nitrous on-set at 80-percent throttle opening instead of 100 percent with a micro-switch.
But the main application for this TPS conversion is still for carbureted cars running a late model electronically-controlled automatic transmission. It’s a great way to combine a traditional carburetor with a late-model automatic overdrive transmission. Likely there are other uses creative car guys can come up with that make this simple device a must-have electronic item – even for a simple carbureted car.
|Accu-Link TPS conversion kit||Call||HGM Automotive|
|Billet throttle position sensor||Call||HGM Automotive|
|Holley TPS conversion||534-202||Summit Racing|
|Innovate TPS Sensor kit||3930||Innovate Motorsports|