The clear rear cover actually...
The clear rear cover actually serves a real purpose. Being able to observe how the oil moves inside the centersection allows Tex's R&D team to determine numerous things-one of which is the best location for the oil pump pickup so that it will not be located inside a pocket of aerated oil. This photo is of cold oil, with the rearend spinning at 1,000 rpm. As you can see, it barely makes it up the back of the cover.
In the course of its studies, Tex Racing determined the need to produce an oil pump with a new style to take advantage of the findings. The result is an internal oil pump that drives off the back of the pinion gear. This direct-drive style of pump, versus a beltdriven pump, has not yet been widely accepted in Saturday night racing classes because a different pump must be installed in each rearend assembly you carry to the track. This can cost a little extra money up front, but Havens says the difference in drag between a direct drive and belt system can easily be 1 hp or more, depending on the type of belt and amount of wear. The Tex Racing pump also uses rotors that are just 0.200 inch thick to bring pumping pressure within spec. A relief valve also vents extra pressure if necessary. The pump is lubricated by the oil in the rearend housing and only needs to be rebuilt whenever you pull your center chunk down for a gear rebuild. Havens says the new pump, while available for any Ford 9-inch rearend, has been particularly well received in the Nextel Cup ranks and has been in winning race cars-including restrictor-plate cars, where minimizing drag is so critical.
Another interesting finding that most Saturday night racers can use is that rearend oil pressure can spike as high as 150 psi if the driveline is brought to racing rpm while the oil is still cold. This often happens in racing if you don't have a chance to properly warm up the car before taking your qualifying lap. Pushing cold gear oil at 150 psi will cost you at least 5 hp, and you can't afford any drag on your driveline during qualifying. Also, Havens says most coolers are only designed to reliably handle 100 psi, and if you are suffering from oil cooler leaks, they quite likely came from cold-oil pressure spikes and not just vibrations from racing.
Havens also stresses that you don't have to take his word for it. If you own an onboard diagnostics system, you can easily configure it to test your oil inlet and outlet temperatures at the oil cooler as well as pressure during a test day at the racetrack. It may not be as precise as Tex Racing's parasitic dyno, but it will give you an idea of exactly what is going on inside your race car.
Here, the rearend is spinning at 2,400 rpm. The oil temperature is rising slowly, and the lighter color indicates aeration.
This shot was taken with the rear gears spinning at 3,700 rpm. The oil being directed over the top of the inside of the housing is dripping onto the carrier bearings as well as the pinion bearing, ensuring that they are properly lubricated.
Finally, we are at racing speed: 7,100 rpm. As you can see, there is lubricant everywhere. This is why it is dangerous to try to lower your lubricant level too much, unless you have an oil pump dropping oil straight onto the ring gear.
Here's the extent of Tex Racing's new oil pump. To keep oil pressure low enough, the pump gears are only 0.200 inch thick.
The pump is driven off of a driveshaft that keys into this hex cut and into the back of the pinion gear. Havens says this is the most efficient system Tex Racing has found so far.
If you race a quick-change rear, Tiger Rear Ends produces a similar oil pump that spins off the back of the jack shaft. Tiger also sells a kit that allows you to mount your oil cooler directly to the axle tube, which is a great way to minimize the complexity of the plumbing.