The Dodge Challenger was available with 3 different sizes of 4-cylinder-in line-liquid cooled engines :A 1600cc, 2000cc and 2600cc
These engines were available in different versions:

USA:
1600cc G32B-K engine without the "silent shaft" system, produced from 1978 thru 1980.
1600cc G32B-K engine with the "silent shaft" system, produced from 1978 thru 1980.
2000cc G52B-U engine was available only in 1978.
2600cc G54B-F engine was available throughout all production years, 1978 tru 1983 in the USA

Canada
1600cc 4G32-K engine without the "silent shaft" system, produced from 1978 thru 1980.
1600cc 4G32-K engine with the "silent shaft" system, produced from 1978 thru 1980.
2000cc 4G52-U engine was available from 1978 tru 1983
2600cc 4G54-F engine was available throughout all production years, 1978 tru 1983


The 2000cc and 2600cc engines came with the silent shaft balance system and are the same except for a difference in bore and
stroke.

The Challengers sold in the USA also had the "MCA-Jet" system



Silent Shaft system: added to mitsubishi engines in 1976, on the Astron 80 engine. It uses two counter-rotating balance
shafts inside the engine to cancel most of the vibrations from within the engine. It received the "Price for Science" from
the Japan's Automobile Technology Association

MCA-Jet: Mitsubishi Clean Air and jet-valve controlled lean combustion, an anti-pollution system that is effective without
the use of a catalytic converter. It prevents pollutions from being burned outside the engine, which is usually caused by
air-injection and rich mixtures. A good combustion mixture is achieved by letting a high-speed jet of air into the cylinder
from a third valve. This causes a better lean mixture and cleans the spark plugs.