After driving our Nova for about 20 minutes in town at part throttle, the part-throttle shifts weren't annoying, and manually shifting the trans was no worse than driving a manual-trans car without the clutch. For a Pro Streetstyle car that does not see thousands of street miles, this could be acceptable. If the trans was new and modified for slightly higher line pressure, it could be really harsh. Our 4L80E was a junkyard refugee, so it doesn't quite have the ultimate shift firmness that a new trans would offer, so the part-throttle shifts are most definitely firm but not neck-snapping. To update the trans back to electronic control at a later date would require a new valvebody. The kit is not that expensive, but it does require removing the valvebody and a permanent change. As the throttle is opened to wide-open throttle (WOT), manifold vacuum approaches zero, which increases trans line pressure to ensure that the clutches see maximum hydraulic application pressure. The old-school vacuum modulator is connected to engine manifold vacuum and adjusts trans line pressure based on throttle opening (load). This conversion requires permanent modifications to mount a vacuum modulator valve to the valvebody. The first idea we ran across was a full-manual conversion kit from Trans-Go (PN 4L80E-3, $232.95 Summit Racing), which converts the 4L80E to full manual use. This pushed us to look for a less expensive alternative. These controllers all did a great job, yet the least expensive Powertrain Control Systems unit was still priced right around $600. Car Craft did a complete comparison of six different transmission controllers for the 4L80E four-speed automatic overdrive transmission in the Mar. All late-model overdrive automatics are now microprocessor managed, which makes converting one of these transmissions more expensive, since it requires a separate, stand-alone electronic controller. This obsession with control started with electronic fuel injection in the late 1980s and eventually expanded into suspension and transmission control. If it's mechanical, you can bet the OEs have it digitally controlled.
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