Dual Dyno Tests Suggest McLaren 765LT Is Seriously Underrated – Motor1

We were ready to be skeptical about this report. Here’s why – Dragtimes put a McLaren 765LT on a chassis dyno and pulled 770 horsepower at the wheels. Remember, wheel power is less than crankshaft power, which is where automakers get their official ratings. In this case, the rating for the 765LT is 755 hp, so either McLaren underrates its engine by over 100 hp, or there’s something goofy with the numbers. More on that in a bit.

We were ready to question everything from the dyno setup to whether the car was stock, but here’s why we aren’t nearly as skeptical as we were at the beginning of this saga. We came upon another 765LT dyno test, coincidentally posted today from Hennessey Performance. And you know what? Their pull was even higher, 780 to the rear wheels to be exact. Yes, 780.

Don’t bother crunching the numbers in your head. We already did the math, and depending on the power loss from the driveline, these stats suggest the 765LT’s twin-turbocharged 4.0-liter V8 actually packs somewhere between 885 and 900 hp. That’s not just a bit more than McLaren claims, that’s in a different freaking solar system. So yeah, with two dynos logging very similar power figures on two separate cars, we’re less skeptical. However, before jumping out of our skin over McLaren’s seemingly hilarious hp understatement, there are some points to consider.

Gearing can affect wheel-horsepower ratings. To get an accurate measure of engine power, using a gear closest to a 1:1 ratio is best. The Dragtimes team made their 770 hp pull in fifth gear, but also tried sixth which returned 757 hp. Hennessey’s pulls were all in fifth, so there’s at least an apples-to-apples comparison. Could sixth-gear pulls be more accurate? That’s info we don’t have handy. And of course, the dyno needs to be set up correctly as well.

Calculating parasitic power loss can also be tricky. Old school automatic transmissions could absorb upwards of 25 percent of the engine’s power, but modern dual-clutch transmissions are believed to be more efficient. The mid-engine design also means no big driveshaft to turn, which reduces power loss. In this instance, 13 percent power loss is a number used by Dragtimes, based on previous experiences and some dual-clutch gearbox info gleaned from Ford on the GT.

Now, here’s the goofy point we alluded to earlier that definitely makes a difference. Both cars were dyno tested running race fuel. The Dragtimes team had 100-octane juice in the tank and the Hennessey crew was living large on 109 octane. We aren’t experts on how McLaren’s engine management system handles tuning for race gas, but the fuel absolutely makes a difference. Case-in-point, Hennessey’s first run on the 765LT returned 747.6 horsepower on 93 octane pump gas and a warm engine. After letting the car cool for an hour – and after dumping 109 octane race fuel in the tank – it hit 780 hp.

Here’s the thing. None of these points and exceptions are enough to get us anywhere close to McLaren’s official 755 hp rating. And you know what? Seeing the 765LT run sub-10-second quarter-mile times is a further indication that, for reasons we don’t fully understand, McLaren is seriously pulling everyone’s chain when it comes to this bonkers supercar.