the first 10 HS in a 250 rating engine and above are 2.0. All the rest you add are 1.4.
If you run a 245 engine, 9 DHS work as 2.0, the 10th you need to add will work at 1.4.
Don't think that adding 2 DHS within a 300 engine (taking advantage of the dual slot inside it) will make those two work 2.0.. they'll act as 1.4 as any other DHS you're going to add beyond the ones provided by the engine.
If you look at mechlab's values, they changed simply because now that value is correct. Before mechlab accounted ALL dhs (even those in the engine) as 1.4.
Edited by John MatriX82, 28 January 2013 - 12:47 PM.