(Can’t believe the engines used to be that small before)
Me neither. Those engines, according to Wikipedia, are Pratt & Whitney JT8D, with a thrust of 14,500–17,400 lbf (64–77 kN).
And the MAX will have 18,000–32,900 lbf (80–146 kN) with he CFM Leap (Leap-X) according to wikipedia!
I never heard about this airline. Nice livery too.