Speedwagon is this guy.
https://vsbattles.fandom.com/wiki/Robert_E._O._Speedwago
Since OP didn't link The Demogorgon I'll link that too.
https://vsbattles.fandom.com/wiki/The_Demogorgon_(Stranger_Things)
I have no idea what The Demogorgons' go to move is, but portal creation seems to give The Demogorgon a good shot at simply BFRing Speedwagon.
Telekinesis might be relevant, both have just regular human lifting strength, and the profile lists the possibility that The Demogorgon may have higher lifting strength via telekinesis which means The Demogorgon could maybe incapacitate Speedwagon long enough to BFR via portals.
The Demogorgons' profile doesn't give any indication that it is a particularly good fighter, so I suppose if it came to hand-to-hand, Speedwagon would probably win.
Speedwagon also has his hat, giving him a good ranged option which would probably work even if Speedwagon was held by the telekinesis. This does depend on how much The Demogorgon can affect at once with telekinesis, because if it can hold both Speedwagon and his hat then things may be different.
The Demogorgons' regen seems kinda irrelevant, and the lack of a specified starting distance means The Demogorgon and Speedwagon will likely be too close for The Demogorgons' enhanced senses to come into play.
From what I see, if The Demogorgon is likely to lead with a portal to BFR Speedwagon, The Demogorgon wins via BFR.
If this is not The Demogorgons' lead, Speedwagon wins via a combination of his hat and his likely superior skills in hand-to-hand.
That all being said, if The Demogorgons' different life stages change this that too needs to be considered.