Gary Portelli is in an experimental mood this week and it is partly inspired by the livewire antics of his Rosehill runner I Can Rock.

A horse who traditionally has his races spaced, I Can Rock has been a handful on the training track, prompting Portelli to send him into a race on a seven-day back-up for the first time in the five-year-old's career.

"I'm backing him up which I don't normally do with him," Portelli said.

"But he's been going berserk at trackwork this week, bucking and pig-rooting. He's off his chops."

I Can Rock has settled off the speed at his past two runs and made late ground, finishing less than two lengths from the winner Mr Manhattan in a 1000m race at Randwick last Saturday.

His three career wins have come on bush and provincial tracks but mindful of some advice given to him by the late Guy Walter, Portelli believes the horse is on the verge of a city victory.

"He's gone from struggling to win one in the bush to being close to winning a Saturday race," Portelli said.

"Guy Walter trained a few from the family and he told me this horse wouldn't come good until he was five or six.

"This preparation, he's just been asking for some daylight at the 300 (metres) and he'll get home over the top of them."

Portelli is also heading into unchartered territory with his other Rosehill runner Testashadow.

The horse hasn't won for almost a year and Portelli has opted to step him up in distance in Saturday's AMWU-National Handicap with in-form apprentice Jess Taylor to ride.

"We're trying him over 1800 metres for the first time because he seems to have got a bit dour," Portelli said.

"The claim for Jess Taylor will suit him nicely and I think he'll run well."

Portelli will be watching his Rosehill runners from Flemington where he has Sebring Sun in the Group One Coolmore Classic.

A $21 chance, Sebring Sun has been freshened since his third to Saturday's odds-on favourite Exosphere in the Golden Rose last month.