Wanderingsoul wrote:
I am planning a truck with a Daihatsu D1100 turbo engine. With the engine behind the driver, I think doing the wiring for the automatic will be less of a nightmare than designing the shift linkage for a T50. Also, the ratios work out much better. Since the computer shift points would be way off with the diesel engine, is it possible to use the auto trans by always shifting with the buttons, paddles or the lever?
The primary consideration must be how you want the vehicle to drive. Even if you are manually selecting the gears of an automatic transmission, the driving experience will be worlds apart from a manual transmission. The torque converter, especially when it's unlocked, creates a mushy marshmallow between the engine and the drive wheels. For a truck that's hauling or towing, this is a great thing. For a lightweight vehicle where responsiveness is prioritized, this is a huge downside.
Any Miata transmission will have two main control components - the mechanical valve body and hydraulic passageways, and the electronic controller that triggers the various solenoids in the valve body. At the very minimum, you will need a standalone transmission controller that will allow you to set your own shift points and/or select your own gears based on a paddle input. Expect to spend a MINIMUM of $600 on the controller, if one even exists that supports the Miata transmission. You'll likely also have to dig into the factory valve body and adjust springs, check balls, and passageways to get your desired behavior. Who knows if the factory torque converter will like your engine/vehicle setup at all - torque curve, vehicle weight, and gearing can all have a significant effect on the torque converter behavior. Automatic transmissions are still a bit of a black art and nothing is easy/plug-and-play.