Dual Dyno testing suggests McLaren 765LT is seriously underrated

We were prepared to be skeptical about this report. Here’s why – Dragtimes put a McLaren 765LT on a dynamometric chassis and pulled 770 horsepower at the wheels. Keep in mind that the power of the wheels is less than the power of the crankshaft, this is where car manufacturers get their official ratings. In this case, the 765LT’s rating is 755hp, so either McLaren underestimates its engine by over 100hp or there’s something wacky about the numbers. More on that in a moment.

We were willing to question everything from the dyno setup to whether the car was stock, but here’s why we’re not as skeptical as we were at the start of this saga. We came across another Dyno 765LT test, published by chance today by Hennessey Performance. And you know what? Their traction was even higher, 780 at the rear wheels to be exact. Yes, 780.

Don’t bother to crunch the numbers in your head. We’ve done the math before, and based on the power loss from the transmission, these stats suggest that the 765LT’s twin-turbocharged 4.0-liter V8 is actually developing between 885 and 900 hp. It’s not just a little more than McLaren claims, it’s in a different scary solar system. So yes, with two dynos recording very similar horsepower figures on two separate cars, we’re less skeptical. However, before we jump out of our skin on McLaren’s seemingly hilarious understatement, there are a few things to consider.

The gearing can affect the rated power of the wheels. To get an accurate measurement of engine power, it is best to use a ratio closest to a 1: 1 ratio. The Dragtimes team put their 770 horsepower into fifth gear, but also tried sixth. which returned 757 horsepower. Hennessey’s sweaters were all in fifth, so there is at least an apple-to-apple comparison. Could the sixth gear pull-ups be more precise? This is information that we do not have at hand. And of course, the dyno must be configured correctly as well.

Calculating the parasitic power loss can also be tricky. Old-fashioned automatic transmissions could absorb over 25% of the engine’s power, but modern dual-clutch transmissions are considered to be more efficient. The mid-engine design also means there is no large driveshaft to turn, which reduces power loss. In this case, 13% power loss is a number used by Dragtimes, based on previous experiences and information about the dual-clutch gearbox gleaned from Ford on the GT.

Now here’s the wacky point we alluded to earlier that definitely makes a difference. Both cars were dynamically tested with racing fuel. The Dragtimes team had 100 octane juice in the tank and the Hennessey crew lived big on 109 octane. We are not experts on how McLaren’s engine management system handles race gas tuning, but fuel absolutely makes a difference. Case in point, Hennessey’s first run on the 765LT returned 747.6 horsepower with a 93-octane gas pump and a hot engine. After allowing the car to cool for an hour – and after dumping 109 octane racing fuel into the tank – it hit 780 hp.

Here is the thing. No of these points and exceptions are sufficient to bring us closer to the official quotation of 755 horses of McLaren. And you know what? Seeing the 765LT run less than 10 seconds in a quarter mile is just one more indication that, for reasons we don’t fully understand, McLaren is seriously pulling everyone’s chain when it comes to this bonkers supercar.