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How the wrong fuel will cripple the power of the Ford Mustang R-Spec

By Andy Enright, 25 Feb 2020 Features

Ford Mustang R-Spec Performance Testing

It’s crucial to put the right fuel in a Ford Mustang R-Spec.

Ford’s Mustang R-Spec has hogged the headlines recently and with good reason.

A car with a five-year factory warranty and more power than a McLaren F1 for less than a hundred grand? No wonder the thing has sold out its 500-car production run in record time.

But that power figure comes with a couple of caveats.

If you read our story on performance testing, you’ll realise that with great power comes great traction requirements, something the R-Spec struggles with.

Vehicle developer Rob Herrod mentioned to us that the ECU is also very protective if it detects engine overheating, a significant part of the reason why Wheels’ times were quicker than those of MOTOR’s (we tested on a day fully 11 degrees cooler).

But there was also another nugget of info that Rob dropped that pricked up our ears. He mentioned a supercharged car arriving at their shop from Western Australia, having ostensibly been fuelled on 98RON petrol.

 filling up the Ford Mustang R-Spec

When it was put on Herrod Performance’s hub dyno, it was found to be a massive 100kW down on what it should have been making. A tank drain and a refill with Shell V-Power (Herrod’s preferred fuel) and the power figure was restored. We’ve heard stories before of fuel being out of spec, causing the car to default to a safe map, but this was something else.

It’s also the case that the R-Spec limits peak power in the first couple of gears. In the real world this isn’t too much of a problem because the torque band is so massive, you’ll probably be in third 90 percent of the time you’re driving it.

In other words, you need to slot a lot of the jigsaw in place to get the very best from a Mustang R-Spec. Do the ends justify the means? Damn right they do.

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