Jenson Button says he is "very excited" to test the upgraded Honda power unit at this weekend's Belgian Grand Prix.

Honda has spent three tokens on updating its power unit, seeking more outright power ahead of races at two consecutive high-speed circuits. While Button is keeping his expectations in check, he admits it is impossible not to be optimistic ahead of testing such an upgrade.

“You still get excited," Button said. "Anything that’s new, you get excited about as a driver. Especially after the summer break, coming to Spa and you’ve got upgrades, you get very excited.

"Even when I’ve had a car for example that was not competitive at all like 2007, every time you jump in the car you think it’s going to be better than the last time. And then you get a rude shock!

"It is different now because at least the car is nice to drive. I do feel it will be a step forward but we just don’t know how much yet. We’ll have to wait and see tomorrow, really.”

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With McLaren set to take grid penalties this weekend as a result of using the new power unit, Button says it's not the worst race for such a setback.

“We’ll start from the back of the grid but to be fair at Turn 1 here you never really know what’s going to happen and we would have been in the mid-pack so it can always end in a wheel missing after Turn 1 so starting where we are is not such a bad thing.

"We might pick up four or five places and I’ve heard the starts are really complicated now! We have to think for ourselves, so I’m scared about that but hopefully it will be a positive with the experience I have.”