ZAZ-968 "Zaporozhets", 1970s
Power ~45 HP (non-British, 736 W/HP) ~= 33 kW.
Fuel: gasoline, consumption ~6 l / 100 km at 80 km/h speed, density ~= 0.75 kg/l,
so ~0.045 kg / km at speed 22.2 m/s.
So, effective thrust = 33 000 / 22.2 ~= 1.5 kN
Mass: 840 .. 1 160 kg, let it be average = 1 000 kg.
So, effective acceleration (in absense of road and air drag): 1 500 / 1 000 ~= 1.5 m/s2.
Tank capacity: 40 l.
So, trip distance = 40 * 100 / 6 ~= 667 km.
Trip duration = 667 / 80 * 3 600 ~= 30 000 s.
Total delta-V = 30 000 * 1.5 ~= 45 km/s.
45 000 = Exhaust speed *ln (1000 / (1000 - 80))
Exhaust speed = 45 000 / ln (1000 / (1000 - 80)) ~= 45 000 / ln (1000 / (1000 - 80)) ~= 45 000 / 0.0834 ~= 540 km/s.
ISP = 540 000 / 9.81 ~= 55 000 s.
***
Once again.
Total delta-V ~= 45 km/s.
Exhaust speed ~= 540 km/s.
ISP ~= 55 000 s.
In Soviet Russia the cheapest cars were having ISP of a thermonuclear torch ship and were able to pass 1 AU in 40 days.
(Ok, in 80 days, as they needed fuel to brake.)