There are some minor detail differences between the Mk 2 and the Mk 2 Plus. The biggest difference is probably that the Mk 2 was designed to use the Silicone Protected Environmental Chamber (SPEC) system while the Mk 2 Plus was modified to use the current non silicone filled Thermal Insulating System (TIS).keyshunter:
They use the same piston and performance is essentially identical.
That said, SP also has a much older Mk 2 design that predated the early 70's through late 1980's Mk 3. These early Mk 2's look a lot older with rounded caps, 3/8" HP ports and only 2 LP ports.
In comparison to the Mk 2, the Mk 3 has a smaller diameter piston head. In between the MK 3 and the reintroduced "modern" Mk 2 was the Mk 200 which had the same number of ports as the late production Mk 3 (3 LP ports) with the larger piston head diameter of the MK 2.
All in all the progression was:
Mk 2 (old style)
Mk 3 (old style)
Mk 3 (new style)
Mk 200
Mk 2 (new style)
Mk 2 Plus
