That's a 2012 McLaren MP4-12C on a dyno.
As Mike Skinner once said, it was supposed to be so easy. We'd test the McLaren MP4-12C at the track, then pop down to the dyno the next morning for an hour (or two, tops) to run its numbers. Easy peasy.
What, is the MP4-12C defecating gold coins? No, the goods under its skin simply make car geeks come out of the woodwork.
Starting with its smooth belly, the MP4-12C thwarted our attempts to make it talk. Finding anchor locations at the rear of the car required removing the carbon fiber diffuser panel, which is held on with an inordinate number of fasteners. And for Pete's sake, be careful with that thing -- its replacement cost is north of five grand. Locating a coil on the engine to attach the dyno's speed pickup was like searching for a decent human being at the Waxman tobacco hearings.
Then came the car's electronic stubbornness. No matter which magical button-pushing sequence was attempted, it either wouldn't allow upshifts, wouldn't give full throttle, the Graziano-sourced 7-speed twin-clutch gearbox would go into automatic mode and stay there, or some combination. Mind you, we had a McLaren engineer manning the factory McLaren diagnostic tool while all of this was going on.
Okay, enough crying. The MP4-12C eventually relented, allowing its power plant to fully open its lungs. Said power plant is codenamed M838T, an all-new twin-turbo, dry-sumped, 90-degree, flat-plane crank'd 3.8-liter V8 that generates 592 horsepower and 443 lb-ft of torque at the flywheel. It has 93 mm bores on a 69.9 mm stroke (bore spacing is 108 mm), making it quite oversquare. This was done to facilitate high revs and to package the large valve diameters necessary to support high airflow rates.
For the tl;dr crew, here's what it put to the rollers of the Dynojet chassis dyno at MD Automotive in central Westminster, California:
Maximum output as measured at the wheels totaled 514 horsepower and 415 lb-ft of torque. More than 350 lb-ft is on tap between 3700 and 7700 rpm, so despite its lofty rev limit (McLaren says 8500 rpm; this car upshifted at 8200), the MP4-12C has a broad, flexible powerband.
Now, we've been spoiled lately by many turbocharged German engines, many of which have put more power to the dyno rollers than than their flywheel ratings suggest. Based on our dyno results and a swag at driveline loss, McLaren, however, does not appear to be under-rating (or over-rating) its engine.
As always, we had 91 octane "premium" fuel in the McLaren's tank. It's anyone's guess whether more octane (like the 93 or 94 octane available elsewhere in this great land) would help bolster output. Our guess is that it would.
Before the test began we wondered if we had enough airflow. The McLaren carries an engine coolant radiator ahead of each rear wheel, while an intercooler radiator (the MP4-12C has liquid-air intercooling) sits beneath each headlight. We had one big fan and two puny fans to cool four heat exchangers. What to do?
After a nervous conversation filled with false confidence, we finally parked a small one at each flank and pushed the big fan away from the car's nose to allow its flow field to envelop the entire vehicle and feed air into the side gills. Then we kept a sharp eye on coolant and air intake temperatures logged by the OBD-II diagnostic tablet.
Heat turned out to be no problem at all. In fact, consistency was a strong suit of the car -- once things got rolling the MP4-12C banged out seven full-throttle pulls with nearly identical results. There was always that "noise" in the data you see north of 6000 rpm, but there were no signs of power-sapping heat soak in the output we measured, and the MP4-12C's fluid temperatures stayed quite happy.
The MP4-12C has an unusual cooling system in that the intercooler pump is not powered electrically, it's mechanical. This pump is piggybacked onto the engine coolant pump. Imagine two impellers mounted back-to-back and driven by the engine via a chain and you've got the idea.
In fact, this smaller pump is the heart of an entire "low temperature" cooling circuit that carries liquid to the charge-air coolers, oil coolers, clutch and transmission fluid coolers (and then those radiators at the front of the car). The larger pump circulates coolant to the engine in a "high temperature" circuit. The two circuits share a common header tank.
Liquid-air intercooling makes for minimal charge-air pressure losses -- the charge-air coolers are located directly between the turbos and the intake manifold.
The MP4-12C's characteristic flat-plane V8 yowl manages to make its way past the sound-damping turbos. Perhaps it's not as spine-tingling a sound as a Lexus LFA makes, but the MP4-12C definitely sounds more exotic than a 911.
Speaking of which, for kicks, here's how the Brit supercar stacks up to the Porsche 911 GT2 RS and Lexus LFA. The manner in which the McLaren produces its power is something of a fusion of these cars' approaches, as you can see below:
Hey, the McLaren generated exactly the same peak power (though heaps more torque) as the Lexus. The Porsche, meanwhile, is a mighty potent thing, no? Granted, the Germans have had plenty of time to develop and hone its flat-six engine.
In a sense the McLaren's M838T engine is just getting started. In eighteen months, the M838T was designed, developed and assembled to McLaren's requirements by engine consultants/gurus Ricardo in West Sussex, England. Those requirements included that the M838T generate 600 PS, 600 Nm, weigh no more than 200 kg (that's 592 hp, 443 lb-ft and 441 lb in Americaland) and provide class-leading fuel economy.
Ricardo met the output objectives, beat the weight target by 2.2 pounds and surpassed the transient response and efficiency goals. Yet on the face of it, the McLaren's M838T is a fairly conventional engine -- it employs port fuel injection, valve lift is fixed (though timing is variable) and its turbos are single-volute wastegated units. Sweating the engine's details meant that other technologies were simply not required to meet McLaren's goals.
Tooling up an all-new engine is a serious financial commitment, and future variants of the M838T are a sure thing. So here's our speculation. Currently the engine has a low 8.7:1 compression ratio; applying direct injection would allow higher compression ratio, collectively bumping output by roughly ten percent. And because the M838T is a flat-plane V8, its firing order means it is ideally suited to twin-scroll turbos. Switching to twin-scroll turbos would improve volumetric efficiency (read: more output) and improve transient boost response.
Plus, Ricardo officials have hinted at some kind of innovative valvetrain as a possible future enhancement. Time will tell.
McLaren's competition won't be sitting still in the meantime, though. We'll keep the dyno warm.