A while back, we brought you this piece on Aston Martin’s new Valkyrie engine, with the main focus being its ability to turn to 11,000 rpm. However, it seems like the astounding power numbers were glossed over by most readers, and questioned by others. After all, a 1,000 horsepower, naturally aspirated production engine, able to turn north of 11,000 rpm off the showroom floor isn’t exactly something you see every day.
EngineLabs readers weren’t the only ones that questioned how the Valkyrie engine was able to make so much horsepower naturally aspirated. Jason Fenske from Engineering Explained heard those same questions. Luckily for us, he was moved to make a video explaining some of the finer details of the 6.5-liter, naturally aspirated V12 powerplant.
Ride of the Valkyrie
To start, the Valkyrie engine is designed and manufactured by the legendary group at Cosworth, and is a 6.5-liter (396 cubic inches) 65-degree V12 layout, with a rated peak power of 1,000 horsepower at 10,500 rpm and 546 lb-ft of torque at 7,000 rpm, with a maximum engine speed of 11,100 rpm. It features dual throttle bodies and a unique 3-into-1 quad exhaust. “That gives it 153.8 horsepower per liter, which blows everything that came before it out of the water,” says Fenske.
“At the beginning of engine development, they made an inline-three-cylinder engine to test whether it could spin as high as they wanted, make the power they wanted, and meet emissions standards,” explains Fenske of the engine’s development. “It worked, and they then scaled up to a V12 design, which is essentially four of the three-cylinder engines, each with its own catalytic converter.”
One thing that has always bothered us from the original article is that while the displacement of the engine is known, no one has ever officially stated the bore and stroke of the engine. However, Fenske is apparently an aspiring detective in his off-time, as he was able to glean a detail from an interview, and then apply his signature engineering prowess to it, to get an idea of the bore and stroke.
“Aston Martin hasn’t actually released the dimensions of each cylinder. However, in an interview with Carfection, Cosworth revealed their mean piston speed was somewhere between 25 and 26 m/s,” Fenske says. Using some simple math and known variables, Fenske is able to bracket the possible bore and stroke using those two figures and say with reasonable certainty that the cylinders feature a stroke between 67.6mm and 70.3mm (2.661 and 2.767 inches). Since the total displacement is known, Fenske is also able to deduce that the bore is between 99mm and 101mm (3.897 and 3.976 inches) in diameter.
Explaining The Power
One thing that seems to be hard for people to believe is the 1,000-horsepower naturally aspirated figure. That brings us to the measurement we recently covered on several fronts with both Jeff Smith and Fenske — Brake Effective Mean Pressure (BMEP). It was the figure a lot of smart folks cited when they didn’t believe the first public dyno test of the C8 Corvette, and in a similar fashion, Fenske cites BMEP to explain why the number isn’t so unbelievable.
As he breaks down the calculations for BMEP, we see that while the Valkyrie engine’s horsepower-per-liter numbers are insanely high, it’s efficiency is near that of a Gen-III Coyote engine, with a 14.3-bar BMEP (the Coyote has a BMEP of 14.2). “14.3 is very good, but it’s not anything unheard of,” explains Fenske. “It’s not like this engine is breaking any laws of automotive physics. It’s well within the norms for a ‘good’ naturally aspirated engine.”
The key to that good BMEP number in a naturally aspirated engine, explains Fenske, is optimizing the airflow into the engine via pulse/wave tuning. By using the positive and negative pressure waves generated by the opening and closing of the valves, designers are able to give the airflow a little kick into the opening valves and bring volumetric efficiency up.
At this point, you might be asking, “how is it making so much more horsepower per liter if it’s torque-per-liter figure is on the high end of the middle of the pack?” The answer to that is three letters: RPM. “Power is a function of RPM. If you hold everything else constant and you are able to rev higher, you will make more horsepower,” says Fenske.
“For this engine, we are making 546 lb-ft at 7,000 rpm. Calculating that out, it gives us 728 horsepower at that same engine speed. With this engine — it’s kind of cool — for each 1,000 rpm you rev up, you gain about 100 horsepower. At 8,000 rpm you’re a little above 800 horsepower. At 9,000 rpm, you’re just below 900 horsepower, and at 10,500 rpm you’re at 1,000 horsepower, with a 13.1-bar BMEP.”
As if breaking down the math like that wasn’t enough to explain that the numbers are realistic, Fenske breaks it down with one more example. “[The Valkyrie’s engine output] sounds crazy, because the number is higher than what we’re used to seeing. If you were to think about a 2.0-liter engine, revving to 5,500 rpm and making 160 horsepower, it wouldn’t sound all that crazy. We’re tripling the displacement of the engine, and then doubling the RPM which doubles the airflow, so it all lines up and stops sounding so crazy.”
Fenske goes on to break down some other features of the engine, such as the gear-driven camshafts at the rear of the engine, as well as the fact that the engine uses port fuel injection, exclusively. If you’d like to hear the discussion of the Fenske’s take on the pros and cons of port-injection vs. direct-injection in this application, he gets into the subject towards the end of the video and is well worth the watch.
All in all, the 1,000-horsepower, naturally aspirated, 11,000-rpm, 6.5-liter Valkyrie engine from Aston Martin is an impressive bit of engineering. Any time you have performance so good, that people immediately doubt it, it a sign that you are doing something right. And to top it all off, the engine is expected to have a 100,000 km (60,000-mile) service life. Is that just icing on the crazy cake, or what?