Turn Timer lengths

The turn timer for Civilization 4 multiplayer has a number of options that are defined by descriptive words, such as "Slow", "Blazing!!!", or "Snail." These names are necessary since the amount of time that is given for turns on any setting is dynamic depending on the era of the game - the length gets longer as the game progresses.

What is the formula for this amount of time? How long does each setting give you on any given turn, and how is it calculated? Additionally, if quick combat is disabled, time is added during each combat - where is this amount controlled?

The turn length is a function of

• Base timer
• Maximum number of units owned by a single civilization
• Maximum number of cities owned by a single civilization

Timer (seconds) = (Base + City Modifier * Max Cities + Unit Modifier * Max Units) / 4

There's also a multiplier for the first turn.

The modifiers for each setting can be found in
...Civilization 4\Assets\XML\GameInfo\CIV4TurnTimerInfo.xml
This file doesn't exist in the expansion directories, so I presume they carry over.

Summary of modifiers:

          Base    City    Unit    First Turn Multiplier
Static    240     3       1       4
Snail     360     36      12      6
Slow      180     18      6       5
Medium    120     12      4       4
Fast      100     9       3       3
Blazing   80      6       2       2

Apparently static is not actually static.

Source:
Function getMaxTurnLen() in source code file CvGame.cpp

The coefficient of 4 was verified empirically by @marshaul. The only nearby hint of this in the source is a comment stating that turn time provided by user in Pitboss mode is in hours while the code actually multiplied it by 3600 * 4 (3600 seconds in an hour). This probably would also be evident deeper in the engine code.