Click here for work in process XD refresh pictures.
I was talking to a friend who knows my cars and has watched them run over the years. I was amazed to learn that he thought I was running Motec fuel controls on the Cosowrth XDs. I have always run the correct original Cosworth fuel control on all my Cosworth motors (XB and XD). I am particularly fond of the one used for the XDs (same one used for the XF and IRL programs) as it has fantastic boost control.
The Cosworth XD was introduced in 1996 and ran through 1999. It was replaced by the XF (and in 2003 XF-E). It is a 2.65 liter V-8 burning methanol and producing in excess of 800 horsepower at 13,000 RPM and 40" of boost. For reference, boost is measured in inches of mercury absolute pressure. Standard atmospheric pressure is 30" (14.7 psi) and thus 40" equates to 19.6 psi or 4.9 psi of boost over ambient pressure. Although they were run to 14,700 RPM in their day, we limit them to 13,500 RPM to reduce stress on the rotating assembly, reduce damaging vibration and generally increase service life. Note: When looking at early XD cars, be aware that the first XD engines used dual round exhaust ports as opposed to the "squished oval" used in the later specification engines. Because of this, the headers that fit the car will not fit the heads on the newer (and only available) XD engine configuration. Headers that fit the newer engine configuration will not fit the higher tunnel older cars. Here is a side by side view of the two different header flanges.
Performance: The XD produced in excess of 302 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 while the XB series two produced 283. Increases in horsepower over the XB are due in great part to improved head design, reduced internal friction and higher operating speeds. A quick comparison of the XB exhaust port to that of the XD exhaust shows a move towards reduced cross section to improve gas velocity. In addition, there was a dramatic improvement in the short side radius on both the intake and exhaust ports.
Construction: The XD, like the XB before and the XF after, is based on a wet lined alloy block with nicasil aluminum liners. Unlike the XB, the four overhead cams are driven from the rear of the engine by a spur gear set which drives two chains, one to each head. The move from driving the cams from the front to the rear of the engine was done to reduce torsional vibration input to the cam drive. To be on the safe side, we have replaced chains at six hours and will refresh the first engine at 12 hours. The first set of chains showed little signs of wear (stretching).
Fuel Control: The fuel control used on the XD is the same as used on the XF and Cosworth's Indy motor. The XD 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 compressor inlet injectors serve to cool the incoming mixture as it is compressed. All injectors are driven directly by the ECU. 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 4 Bar or approximately 60 psi in the vintage configuration. There are provisions on the engine for changing the fuel pressure while the engine is running, however, Cosworth did not feel it was appropriate to provide this technology to the vintage community. Fuel is supplied by a mechanical fuel pump located in the fuel cell. The pump is driven directly from the XD's right side scavenge pumps by a couple of inch long square drive quill. The XD fuel system must be purged of corrosive methanol after each use (weekend). 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 operator can pick an ECU program with a pickle map that fires the PCI injectors at low rpm while leaning the mixture significantly from that required running methanol. One of the pleasant benefits of the XD is that the fuel map selector on the steering wheel can be set such that one of the settings is a pickle map. The dash is then told that ECU is in pickle mode so that an alarm will warn the driver if he tries to drive off in pickle mode.
On start-up of a pickled engine, the fuel must be removed from the loop before the engine is connected to the fuel cell. The cell is made of natural rubber to resist Methanol and will not tolerate Gasoline. This de-pickling is done simply by connecting the fuel cell's pressure output to the XD's inlet, routing the XD'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 XD'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 XF uses a variable reluctance cam sensor as opposed to the hall effect sensor used on the XD. All the fuel controls were modified to use a VR cam sensor and thus Cosworth had to improvise a bit when they began supplying XDs to the vintage community. There answer was to remove the cam sensor input altogether (a firmware change) and guess at 720 degree synchronization. If the engine starts, off they go. If it does not, the control tries the "other" 720 synchronization. It will switch back and forth until the engine starts. Apart from a backfire every so often, the system works very well. On caveat however, when pull starting a stalled car you must take care not to pull the car too fast! There is a cut off RPM above which the control either thinks it has started or that it will not try to find synchronization. Just pull the car slowly, pick a gear that provides 1200 to 1500 RPM, and be ready to use the clutch. You have no RPM indication from the ECU so it will take a bit of practice to get it right every time. I tended to need a few tows in the beginning so I had plenty of opportunities to learn.
The XD employs automatic boost control (ABC) and no lift to shift technology. The ABC works by controlling the top can pressure (TCP) on the waste gates to open them or close them as needed. The waste gate control is used in conjunction with a 9th butterfly under ECU control at the inlet to the plenum. The ECU then controls both to keep extra boost built up against the 9th butterfly so that lag is reduced when the driver opens the throttle. The added complexity of a 9th butterfly, TCP control solenoid and the extra TCP pressure sensor are well worth it. Boost lag is greatly reduced over the XB and, as a result, the cars are a lot easier and a lot more fun to drive.
The no lift to shift is very useful as well. A potentiometer on the transmission tells the ECU the position of the shift drum. There is also a switch on the shift linkage that tells the ECU when the driver is selecting the next higher gear. When that selection is made, the ECU kills the engine until it sees the shift drum approaching full engagement for the next gear. The system takes a little tweaking for driver and gear ratios but, when right, works very well to protect up shift dog rings. I now replace gears for wear on the tooth face and not because I have destroyed the engagement dogs. However, there is still and opportunity to tear up the downshift side of the dog as there is no help from the ECU for this function. Lastly, that pesky switch in the shift linkage is VERY sensitive. Do not get near the lever until you are ready to use it or you'll get a nasty little hesitation that makes you think you just lost your motor. When you do pull, pull hard and sure and the same way each time. If you are consistent, the box will work flawlessly.
A quick note on data acquisition- The Pi systems originally run on XD cars is no longer available. I spoke with Pi regarding support of the older systems should I buy one from one of the teams and was told they would not supply software nor would they fix the unit if it had a problem. The best they could offer was to sell me a much cheaper (and less capable) club system. As with the XB cars, I choose to use the Motec system. Unlike the XB cars which only required a template rewrite on the Motec side to work, the XD fuel control passed a good deal more information in a greatly expanded message format. Motec took one pass at providing a serial interface for the newer message format but this failed when the car was started. As there are not hundreds upon hundreds of XD ChampCars out there requiring Motec systems, it was unreasonable to expect Motec to spend any more time troubleshooting the problem. The end solution involved twelve hundred lines of 8051 microcontroller assembler and a dedicated translation board. In short, the small board takes the XD data stream, pulls out all the useful information, repackages it in XB format then sends it off to the Motec dash. With this approach, you can log all the relevant engine data including Automatic Boost Control elements to aid in setting the No Lift to Shift strategy and monitor turbo charger performance. I even have an alarm set to warn when boost levels fail to reach the Boost Set Point (steering wheel switch controlled) levels at better than 80% throttle and above 10,000 rpm.
With the release of Motec's second generation Dash you get direct USB download support and expanded serial templates. The 96 Visteon Lola uses the newer Dash and does not require the translation board.
