Back On The Road
Following initial break-in, driving the T/A on the highway has taken on new meaning for Melvin, even in Economy mode with the default programming still in place. "I have always enjoyed the power and the performance of the SD on the road, but highway driving has been stressful, even with the 3.08:1 rear gears," he laments. "I've been spoiled by late-model cars that cruise down the highway in overdrive at much lower rpm. With the T/A, I always had the sense that the engine was working more [and wearing more quickly] than it needed to." Imagine what it would be like if the Pontiac had 3.55s or 3.90s out back.
With an 800-rpm drop at 75 mph thanks to the overdrive gear, the SD-455 T/A has a new character on the highway. "I can actually hear things that I've never heard before-like the radio! And a squeak I have to fix," Melvin says. "At first, I was concerned that adding the OD trans with the 3.08 gear would make the engine lug and feel lethargic in OD, but it hasn't been the case. The T/A still feels powerful, but it's quieter and the engine seems less labored at highway speed." With an effective rear gear ratio of 2.31:1 in OD you can see why Melvin was initially concerned.
Though around town fuel mileage gains will be none or negligible at best, out on the highway, we did document an improvement of 4.1 mpg based on driving four one-hour-and-fifteen-minute test loops at a steady 70 mph.
| HIGHWAY RPM CHANGES |
| MPH |
RPM OD |
RPM w/o OD |
| 55 |
1,600 |
2,250 |
| 60 |
1,750 |
2,400 |
| 65 |
1,900 |
2,500 |
| 70 |
2,100 |
2,750 |
| 75 |
2,200 |
3,000 |
Since most vintage Pontiacs...
Since most vintage Pontiacs will be running a carburetor, we'll illustrate how to set up TCI's remote TPS on another car. It's mounted on the fenderwell, the cable runs over to the engine, and is attached to a bracket and the throttle linkage.
The connectors were plugged...
The connectors were plugged in on the driver's side of the trans. C5 is for the input speed sensor located forward on the case about halfway up. C7 is for the output speed sensor midway up the case toward the back of the trans. C1 is the large connector at the lower rear of the case, which controls all of the internal solenoids. In the next issue we'll discuss programming the trans.
TCI's combination bracket...
TCI's combination bracket retains both the throttle cable (upper) and the TPS cable (lower). After attaching the cable to the carb linkage, it is adjusted by setting its length at the carburetor, so the TPS is able to travel its full range from closed throttle to wide open throttle (WOT) as the carb linkage travels from closed to WOT. Then the hardware is tightened to lock in the setting.