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Cosworth XB Series Two Email Questions or Comments

acquisition The XB Series Two was last run in mass in 1995; with but a few teams running the engine in 1996. It is a 2.65 liter V-8 burning methanol and producing in excess of 750 horsepower at 12,000 RPM and 45" of boost. For reference, boost is measured in inches of mercury absolute pressure. Standard atmospheric pressure is 30" (14.7 psi) and thus 45" equates to 7.35 psi of boost over ambient pressure. Although they were run to 13,200 RPM in their day, we limit them to 12,000 RPM to reduce stress on the rotating assembly, reduce damaging vibration and generally increase service life.

Performance: The Series Two engine produced in excess of 283 horsepower per liter of displacement. For comparison, a very well built normally aspirated Hayabusa engine with nearly the same displacement per cylinder produces 188 horsepower per liter on gasoline. I have included a picture of a "Busa" piston placed on an XB head as a comparison of the difference in bore (with a corresponding difference in stroke). There is also a picture of their respective intake and exhaust valves in addition to a picture of their respective heads. In the end and side views of the valves, the left side is XB while the right is Busa; the top being exhaust.

Construction: The XB, like the DF before and the XD after, is based on a wet lined alloy block with nicasil aluminum liners. The pictures below show the intricate nature of the casting and the quality generated by Coscast. The four overhead cams are driven from the front of the engine by a spur gear set which drives two chains, one to each head. Chains are replaced at ten hour intervals when using a 12,000 RPM limit.

Fuel Control: The fuel control used on the XB is the same as used on the HB. The XB uses sixteen primary Bosch Motorsport injectors, two per cylinder, and four side feed Bosch injectors arranged in a ring, called the PCI, at the turbo compressor inlet. The sixteen primary injectors are driven directly by the ECU while the PCI injectors are driven by the ECU through a separate PCI amplifier. Note: the PCI injectors were changed from the early XBs to the later XBs, XD, XF, and XFE. See the note on PCI Injectors for an explanation. Fuel rail pressure is 8 Bar or approximately 120 psi! Atomization at this pressure is a sight to behold. The compressor inlet injectors serve to cool the incoming mixture as it is compressed. Fuel is supplied by a mechanical fuel pump located in the fuel cell. The pump is driven directly from the XB's right side scavenge pumps by a couple of inch long square drive quill. The fuel system must be purged of corrosive methanol after each use. This is done by disconnecting the feed from the fuel cell and looping the pressure side back to the return. The engine supply and return is then connected to a separate "pickle" tank that supplies gasoline under pressure and provides a dump can for returning methanol from the engine's fuel rail. The ECU can be programmed with a pickle map that fires the PCI injectors at low rpm while leaning the mixture significantly from that required running methanol. In practice, I use a separate ECU programmed with the pickle map. The XD fuel control has a nice feature in that the Pickle Map can be configured to be one of the settings on the steering wheel mixture control.

When restarting a pickled engine, the XB fuel rail must be purged prior to connecting to the fuel cell. The fuel cell is made of natural rubber to resist Methanol and will not tolerate Gasoline. This is done simply by connecting the fuel cell's pressure output to the XB's inlet, routing the XB's outlet to a separate catch can then starting the engine. Once you have clear methanol entering the catch can, you can kill the engine and connect the XB's return to the fuel cell. All this is worth the ability to run a turbocharged engine at these kinds of output without the need for a heavy intercooler.

The XB services communications via a separate (from the ECU) communication controller. The box usually sits on the radiator inlet pod and has three Lemo connectors on it. The ECU communication link is supplied to the controller which separates and manages communication with the Cosworth proprietary port and the data acquisition system data feed. The Cosworth link is used to monitor the ECU and reprogram maps. One leg of the RS-422 data acquisition feed can be connected directly to the Motec dash's RS-232 data input. See Data Acquisition for more details.

Service Life: The XB is remarkably affordable to run in vintage racing when run to 12,000 RPM, 45" of boost and set to 6% rich. To date, my engine builder has been changing cam chains at ten hours and performing a refresh at twenty. Ring seal does not deteriorate appreciably in twenty hours so refresh periods are dictated by service to the valve train. Springs are replaced at every refresh with valves every other. Nicholson Mclaren purchased a large number of XBs from Cosworth along with all of the spares and rights to continue making parts. They have used the engine for several projects thus ensuring a continuing supply of refresh spares. I have also had luck sourcing the more expensive parts (valves, liners, etc.) from original vendors.

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