The Weird Science Behind the World’s Fastest Car’s Wild Engine
We expect speed records to be set by deep-pocketed global automakers like the VW Group’s Bugatti brand, which has the budget to produce completely complicated W-16 quad-turbo engines. So when the independent, Washington-based SSC Tuatara managed to set an official two-way average speed record of 315.7 mph (!) With a small-block engine with half the number of cylinders and turbo and a single camshaft (billet), we were desperate to learn more about this record engine. Who better to tell us about it than its architect, Tom Nelson, of Nelson Racing Engines?
Small block geometry, without GM parts
Tom quickly noticed that this was not a GM engine block. It simply shares some key geometric dimensions with the iconic and quintessential American V-8. But every detail is optimized for this extreme duty cycle. The block is cast and not billet machined, as this is the only way to properly heat a block. Billet blocks need to be built, executed, and then completely remanufactured after hard operation has finished their heat treatment. The top three secrets to generating 1,750 horsepower from this 5.9-liter twin-turbo V-8 include a flat crankshaft, 8,800 rpm redline, and E85 ethanol fuel (horsepower drops from 1,750 to 1,350 horsepower on 91 octane gasoline).
Why a flat plane crankshaft?
As we’ve already noted, the world’s first V-8s had flat-plane cranks because they were essentially two four-bangers sharing a crankshaft; Cadillac’s invention of the cruciform crank (transverse plane, with jets offset by 90 degrees) in 1923 allowed for a more even shot for considerably smoother operation. Flat planes were reintroduced on the high-performance V-8s because the exhaust pulses in the manifold of each bank of cylinders promote more efficient sweeping at high engine speeds. They too sound awesome, that’s largely what founder Jarod Shelby was looking for. As demonstrated by General Motors in 1970, this sound can be reproduced with elaborate, long “180 degree” exhaust manifolds that combine the exhaust from two cylinders on the opposing sides of a V-8 running on an engine. cruciform crank. Nelson’s team looked at such a header for the Tuatara, but the runners’ lengths are so different from cylinder to cylinder and the packaging is so tortured that they gave up on the idea. in favor of a flat crank.
How can this 5.9 liter flat crank engine survive 8,800 rpm?
First of all, this is a very large bore (4.125 inch), short stroke (3.375 inch) engine, which significantly reduces the speed of the pistons at high revs. Then the rotating mass is reduced to a minimum, with short skirted aluminum pistons and titanium connecting rods that end up with a total rotating mass per cylinder of around 1600 grams, including the oil tolerance. Then the team spends two full days precisely balancing the entire rotary assembly (“We can run it at 10,000 rpm and put a wine glass on the balancer,” Nelson said) . Finally, to isolate vibrations from the rest of the vehicle, the engine is mounted using proprietary oil-filled mounts instead of urethane. Oh, and Bryant Crankshafts are providing the crank, which is machined from TimkenSteel billet and would cost $ 10,000.
Patented double scroll turbochargers
To take full advantage of these regularly spaced exhaust pulses in each manifold, they are placed in separate passages to strike the turbine wheel 180 degrees apart. This allows larger turbos to wind up as quickly as a smaller one would with all exhaust pulses unevenly synchronized, all hitting the turbine wheel in the same spot. The patents cover a new aerodynamic form of exhaust turbine and compressor blade designs. Also new: the left and right turbochargers are symmetrically opposed and rotate in opposite directions. This ensures that the exhaust flow is the same on each bank. Nelson claims that these turbos have demonstrated 82% efficiency on the turbocharger map (compared to 70% for most turbos). Boost pressure can go up to 30 psi, but the record run indicated a peak boost at 19 psi. Also note that it is do not a hot-vee design; the turbos sit on the outside, with the intake manifold in the vee.
Extreme intermediate cooling
Generating a big boost is great, but only if you can cool the load. Here, two air-to-water intercoolers are integrated into the billet-machined intake manifold, which is powered by two electronic throttle bodies. During the record-breaking race, the engine’s sensors measured the 260-degree air exiting the turbocharger, with that temperature being reduced to 130 degrees after the intercooler. Nelson notes that every 10 degrees (F) drop in temperature is good for about a 1% increase in power. These temperature sensors are just a few of the many used to measure all aspects of this highly strained engine. There are 11 exhaust gas sensors, four air-fuel ratio sensors and a myriad of pressure sensors. The safety parameters of the motor are closely monitored to ensure that it never inflates. A 10% variation in any specification triggers an alarm / limitation mode. All of this sensing aids in communication to manage torque during gear changes and in conjunction with the traction control developed by Light Racing, which is absolutely essential to reducing so much power through the rear tires.
Other dimensions and ends of the motor
The oiling system is of a dry sump design with a heavily deflected oil sump to enable the extreme on-track riding the Tuatara was developed for. The engine’s cooling system is pretty unremarkable, except there’s a booster water pump in the nose of the car to help move all the coolant to the front radiators. A “ring of flame” helps secure the block to the cylinder head and contain the immense cylinder pressures associated with generating 1,750 horsepower in a 5.9-liter engine. This “hoop” involves drilling a recording groove around the top of the cylinder, into which a hardened steel ring is inserted. This ring indexes into a cylinder head receiving groove and locks the cylinder head gasket in place to prevent it from blowing. And finally, in the Friday practice before the record, the team were unhappy with the exhaust temperatures and traced the problem to coils that were not returning to the ground quickly enough above 6,000 rpm. This effectively over-advanced the ignition timing. Inserting a resistor between the coil and ground rectified the problem, reducing temperatures from 1900 to 1700 degrees. And that’s how this engine of development has survived for so long, and why SSC has enough confidence to sell it to a consumer. For its part, Nelson Racing is eager to build the next iterations of this wild V-8.