Red Bull has certainly raise the performance of its RB13 with the significant upgrade package was introduced at the Spanish GP on last May.
“The car is getting stronger and stronger under race conditions, and again it was a very competitive Grand Prix for us in Hungary,” said Horner.
“So if we can just find that little bit more engine performance… You saw in qualifying that Max [Verstappen] was second-quickest in Q1 and Q2, but you get to the latter part of qualifying and you need that little bit extra to go with our major competitors.”
Horner is doubt, Renault can provide extra pace soon from its engine given that properties are now mainly dedicated to its 2018 power unit which it hopes will be on a par with its rivals.
He added: “I think you need to speak to our engine supplier to understand what their thoughts are regarding engine introduction.”
Looking ahead to Spa, the Red Bull boss believes their chances of success are nothing more than “reasonable”.
“Hopefully we can be reasonable there,” he said. “Austria, we were reasonably competitive there – I think particularly on Sunday.
“On Saturday we are going to struggle. I can imagine us being fifth and sixth on the grid on Saturday and quicker than that on Sunday. The thing I can say about Spa is that you have the ability to overtake there.”