The main difference between the two categories is the level of modification allowed. IT cars use all stock bodywork, have limited attachment points for the roll cage, and very limited engine modifications. Imagine them as what a street car would be if it were optimized for track use (though there is no way that they are streetable in any sense when done right). Production cars allow a lot more in the engine: alternate pistons, lightened rods/crank, cams, lightweight lifters, higher compression; a lot more on the body: alternate material fenders/quarters/hoods/deck lids; more on the chassis: reinforcements, cage connection points, motor mounts, ride height. To get a feel, take a look at the thread I have in our Paddock area about helping a friend build an F Production Scirocco 1.
There are two flavors of Production cars: Level 1 and Level 2. Level 2 was created with a few more restrictions to make it easier to put more "modern" cars into classes that originally were filled with MG Midgets and other very small engined cars. The Scirocco build is a Level 1 car in F Production. My car would be a Level 1 prep level in F Prod as well, but initially I will build it as a Level 2 car in H Production. This means the compression ratio on the engine is limited to 12:1 vs unlimited, the cam lift is limited to .425" vs unlimited, I cannot use a dry sump and I would take a big weight penalty to use a "dog box" racing transmission.
The goal is to gradually make the changes needed over the course of 2013 to have a competitive HP car for the 2014 season. The first order of business will be the body and chassis. I recently rolled an extra shell of an 85 Golf into the garage and we are getting started to make forms for new bodywork molds off of that car. At the same time there is weight reduction and wiring changes to be made on the race car. These two things will probably take up all of the winter months. After that there will be a round of suspension changes, to get things set up properly for the new racing slick tires (much different than the DOT approved race Hoosiers that we have been using), and finally we will get to a proper engine build. I will try to keep updates going on here fairly regularly - or at least once a month. It should be a fun ride. If anyone is interested in working on a project like this, let me know. I would be happy to teach what we are doing along the way, and very appreciative of the extra help.
Here are some current state pictures:
