Trainer Brock Lewthwaite dares to dream big and is not shy to suggest that Fat Roy Slim could be his Perth Cup (2400m) contender.

Brock Lewthwaite is certain Fat Roy Slim has the ability to follow up in big Ascot races after completing a breakout summer and autumn campaign.

Fat Roy Slim commenced his preparation in January, but was doing his best work six months later when he reeled off five straight wins.

The five-year-old launched his winning spree at Pinjarra and headed for a well-earned rest after dead-heating with Strike Now at Belmont.

Lewthwaite toyed with the idea of Fat Roy Slim having another run in Sunday's South-West Cup (2200m) in Bunbury, but changed his mind.

"He's gone to the paddock," Lewthwaite said to The Races WA.

"The plan is to bypass Bunbury to just give us more time to prepare for the Perth Cup.

"We have our sights on the Perth Cup and we'll work our way back from there.

"He couldn't have done much more than what he's done."

Lewthwaite cannot pinpoint Fat Roy Slim's rapid improvement, but credits his father, William Lewthwaite and jockey William Pike with much of the success.

"I definitely think Willy (Pike) is a big thing to do with it," Lewthwaite said.

"I think my dad did a great job with the horse too.

"Dad did the hard yards and I've come and got the polish.

"It's a pretty cool thing, actually.

"He was dad's last winner and my first win back."

Fat Roy Slim kick-started his racing life under top horseman Stephen Miller before being transferred to Lewthwaite's father.

William Lewthwaite had 13 races with Fat Roy Slim after his son was rubbed out and suspended by WA racing stewards for a year.

Lewthwaite says having Fat Roy Slim back in his care and guiding his future is the spark and motivation driving his comeback.

"It's amazing, six months ago it was looking as hard as ever," Lewthwaite said.

"Six months later it's looking as easy as ever.

"Dad got back yesterday (Monday) and I haven't seen him for most of the year for obvious reasons.

"To have him back and for me to have the band well and truly back together is a great feeling.

"I've been the rookie, had a couple of trips around the sun, there's no time for another comeback after this.

"I want to ascent and I'm here to stay."