When the 49ers’ defensive performance from last year was referenced in a question to Quinton Dial, the lineman swatted it away like a 150-pound guard.

“We’re focused on what we can do now,” Dial said. “If we talk about what happened in the past, then s—, we’ll never move forward.”

Yes, the memory of the 49ers’ 2016 defense is still inspiring expletives.

Last year, the 49ers were historically defenseless: They established an NFL record for most consecutive 100-yard rushers allowed (seven), and ranked among the top 10 in league history in most points (480), total yards (6,502) and rushing yards (2,654) surrendered.

No wonder Dial’s teammates are echoing him when the memory of what they endured is invoked.

“Last year is last year,” defensive tackle Arik Armstead said. “That’s the past. Looking forward, I feel we’re going to be very successful.”

Typical pie-in-the-sky summer chatter? There is evidence that suggests the defense could jump from abysmal to, at least, average.

In April, the 49ers added two first-round picks – defensive tackle Solomon Thomas and inside linebacker Reuben Foster – to a unit teeming with other high-end selections. The 49ers could open the season with six first-rounders among their 11 starters and none could be labeled a bust.

Of course, one of their myriad issues in 2016 was that many of those other first-rounders – Armstead, cornerback Jimmie Ward, safety Eric Reid and defensive tackle DeForest Buckner – didn’t stay on the field. The quartet combined to miss 20 games during an injury filled season that saw their best player, All-Pro linebacker NaVorro Bowman, sustain a season-ending torn Achilles in Week 4.

The 49ers limped to the finish with a spare-parts roster, but now they are talking about teeming with depth along their front seven.

After ranking 19th in sacks, their defensive line could feature Armstead, Buckner and Thomas, with free-agent linebacker Elvis Dumervil, 33, who has 99 career sacks, coming off the edge in passing situations.

“I think that we’re so deep at D-line and the linebacker position with guys who can rush the passer,” Armstead said. “I feel like even our 2s (backups) are 1s (starters). I don’t even see 2s in my head. I feel like we’re all 1s and we’re going to send them in waves.”

Said Robinson: “We’re trying to carve out something great, something special, this year.”

It’s easy to make such statements, but the 49ers will have to answer plenty of questions as they switch to a 4-3 defense.

Can Ward, who hasn’t participated in training camp because of a hamstring injury, successful move to free safety, one of the most vital position in their scheme? Can Armstead, 6-foot-7 and 275 pounds, transition to playing the “Leo” position, the primary pass-rushing spot which is generally manned by smaller players? Can an unproven cornerback – possibly Dontae Johnson or Keith Reaser — emerge to start opposite Robinson? And can rookie defensive coordinator Robert Saleh, 38, prove he’s worthy of his role just three years after first becoming a position coach?

During the offseason, players have consistently said Saleh’s scheme is straightforward and will allow them to play faster. Left unsaid: Last year’s defense under Jim O’Neil had their minds swimming.

“I think he’s simplified this defense for us and it will allow us to go and make plays,” Dial said. “I think he’s bringing some good stuff to the table for us.”

After a year filled with bad stuff, the 49ers clearly have the potential to make a leap, but Dumervil isn’t adding to the hype before his 12th NFL season.

“I hate throwing the word potential around,” Dumervil said. “For me, (talking about) potential means you haven’t done anything yet. So I stay away from potential. But I think we’re working in the right direction.”

Eric Branch is a San Francisco Chronicle staff writer. Email: EBranch@sfchronicle.com Twitter: @Eric_Branch

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