"I would probably say the Ireland game is more mental than physical because we have never been in this position before, whereby we can push even further on," number eight Vunipola told British media.
"It is the day after St Patrick's Day, it is going to be very, very emotional, so we are going to have to turn up with the right mindset to try to negate everything that they are going to bring.
"The grand slam was our goal at the start of the tournament and we're firmly pushing towards it."
England have seen a major turnaround in the last 18 months under coach Eddie Jones, having suffered an early exit from the World Cup they hosted in 2015.
Vunipola believes they are closer than ever to achieving their target of overhauling New Zealand, whose record of 18 straight wins they matched on Saturday, at the top of the World Rugby rankings.
"We've come a long way. I think Eddie and his coaching staff have pushed us massively to a goal at which everyone would have laughed at the end of the World Cup, but now it's realistic," he added.
"If you win 19 games on the trot, you are pushing it. We know we're not number one yet but we want to do things within our power to show we are serious about this goal."
(Reporting by Hardik Vyas in Bengaluru)
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