With the oil pan baffling complete and the engine sealed, it is time to give some attention to the external engine components. The first parts actually fall more into the engine management category than anywhere else, but the crank angle sensor and crank trigger wheel must be installed at this point before the water pump housing and pulleys can be.
Most people don't pay much attention to crank trigger wheels, but it is important when you look at the factory unit. The OEM trigger wheel utilizes a 12+1 arrangement with two variable reluctor crank angle sensors (commonly called magnetic sensors). One sensor reads crank angle 12 times per revolution (once every 30 degrees), while the other senses reference for each rotation.
Full Function Engineering's 60-2 trigger wheel kit replaces the factory setup. A 60-2 trigger wheel has 58 actual teeth spaced 6-degrees apart and a gap where 2 additional teeth would be. That means that the Full Function Engineering (FFE) trigger wheel has six times more resolution than the factory trigger wheel and utilizes the gap in the teeth to reference each rotation of the eccentric shaft. This extra resolution will allow the ECU to control the engine with greater precision.
Because the FFE trigger wheel uses a gap in the teeth to reference each rotation and the fact that a rotary engine only needs 360 degrees worth of crank angle information for sequential injection and/or direct fire ignition, a single crank angle sensor is used to replace the two factory sensors. In this case, the two variable reluctor sensors are replaced with a single Hall Effect sensor. These two types of sensors operate in significantly different ways, but the important functional difference is that a Hall Effect sensor is less prone to signal interference than a variable reluctor. This can become a problem when the crank angle sensor wiring is run near the ignition system.
Now that the crank trigger wheel and main pulley are installed, the water pump housing, water pump, alternator, and associated pulleys need to be installed. Since this is a track car with many components removed, the pulley system is far from stock. The original system contained two belts; one that drove the main pulley, water pump, alternator, and emissions air pump and another that drove the power steering pump and A/C compressor. Because the air conditioning and power steering have been removed, the accessory belt is not used. The OEM main pulley is nice because it is a two-piece unit that can be separated to facilitate this change. We have also removed the emissions air pump because we are running a large single turbo and an aftermarket ECU. This leaves the main pulley driving a single belt for the water pump and alternator.
At this point one might say “Wow that is an extremely simple setup” and while this is technically true, there is still one complication to overcome. With the factory pulley setup the emissions air pump pulls the belt routing away from the centerline of the engine and, in a way, acts like an idler pulley. When you remove the air pump, the route the belt takes is nearly a straight line between the main and alternator pulleys, leaving the water pump with almost zero contact area.
The way many people fix this problem is by increasing the diameter of the water pump and alternator pulleys to break up the straight line and give more contact area to the water pump pulley. This does work to an extent and is how the pulleys were configured on the original build of this car, but it is still not the optimal solution since it underdrives the water pump and alternator in an attempt to engage the water pump pulley.
The better solution is to implement an actual idler pulley to take the place of the emissions air pump and Pineapple Racing have developed two pulley kits that do just that; one for use with the stock twin turbos or a smaller, more rear mounted single turbo and one for use with a larger single turbo. This project features the latter of the two known as the “BT” (big turbo) model.
There are a great number of things that are often overlooked when building a car, several of which were covered today. With any luck we can avoid as much of that as possible during this build and end up with an awesome RX-7. There is a lot to do and this is only the beginning, so stay tuned for the next update.