I decided to throw the following description together in an attempt to explain and hopefully clarify the difference between "i" and "s" models. The information below is based on a chart given on the mazda.com
site, and therefore really only applies to 2005 model year cars in the US (but probably holds true for 2004 cars as well).
The 6 comes with two engine choices, the 2.3-I4 and 3.0-V6. Models with the I4 engine are referred to as "i" models, whereas those that have the V6 engine are referred to as "s" models. That's it, and if this is all you know about "i" vs. "s", then you won't be missing out on much.
But, to continue on a bit...
The 6 has three main body styles:
- 5-door (aka hatch)
The sedan has these variants:
The base variant only comes with one engine type, the I4. The sport and grand touring are offered with both engines (I4 and V6).
The 5-door only has one variant, namely sport. The sport variant comes with both engine choices.
The wagon also has the same three variants as the sedan (base, sport, grand touring) but, unlike the sedan, the wagon does not come with the I4 engine. All variants come with the V6 and therefore are all "s".
The rest is really up to which appearance package(s) has been applied to the car. Using the sedan base as an example:
The car comes standard with 16" steel wheels, however, 17" alloys can be bought as an accessory, or part of an appearance package. Other available options for a base sedan are:
- sports grille
- rear wing spoiler
- power seat for driver
- 6 CD changer
- side air bags/curtains
- moon roof
Here's what's not an option on a base sedan (according to mazda):
- integrated fogs
- electroluminescent red gauges
- 6-speed ATX.
- automatic climate controls
So, you're starting to get the picture, I hope, that a base sedan (or any model for that matter) can be accessorized and thus made to look like a "higher" model. This process can be undertaken by the owner or by the dealer, before or after the sale of the car. Sometimes dealers will apply certain packages to all their base model sedans by default, just to make them more sellable. This however does not change its "i" vs. "s" designation.
To continue this discussion for all remaining variants of the sedan, the 5-door and the wagon would take forever. You can therefore imagine how many other possibilities exist that haven't been described yet.
Finally, throw a wrench into the works and consider that up here in Canada the designations and potential options are again all different.
Quite simple really... right