Depends on who the E4 is. Depends if Sceptile & Infernape can beat one without needing the help of other Pokemon contributing by lowering them down. Certainly? Nah. Gamble? Yeah.
Blaze Infernape has shown honestly more power that E4 base aces in Blaze(except for Flint's Infernape possibly), the only reason it will be not able to beat E4 base aces is because Blaze activates at low health, but that should be enough to beat E4 non-aces.
Sceptile feat against Darkrai pretty much tells that while it would possibly barely loose an E4 base ace, it should obviously able to beat an E4 non-ace.
And what we saw from Ash-Greninja and Pikachu in Kalos, they both definitely would be able to beat an E4 base ace, with Ash-Greninja possibly being able to beat an E4 Mega ace as well. BW Charizard (assuming it improved a lot from BF should be also to potentially beat an E4 non-ace.
Overall, it'll be a very close fight, and Ash only loses if the E4 member has a Mega.