There are a few reasons why the CFI seems to hold up to boost.
Red Beard makes an excellent point that many people I believe often disregard. The factory air box leaks like a 8-71 Detroit Diesel leaks oil. Anybody ever checked the throttle bodies in 400 miles? If you have, then you know how much debris is getting sucked into the motor on a stock CFI. The air box allows excessive belt dust , and other debris ie (metal from cutting running boards and drop n rolls) that accumulates under an engine. Don't even try to argue with me on this. I've seen with my own eyes what ends up under the engine after one of these actions have occurred. Dust, dirt, and pollen from summer strorage, leaf remains, pinecone remains, etc. Don't laugh, I've got a 2010 in my garage right now with 1/8" of sand throughout the motor dept. The turbo'd CFI does NOT have this issue.
Turbo kits of course bring the fuel requirements up to where they need to be. The stock mapping does not provide adequate fuel especially in the mid range. Anybody that has run EGT's with a 20% increase in fueling on a stock CFI knows what I'm talking about.
The other reason these motors seem to thrive on boost is the extra heat the turbo creates most notibly on the piston. Many believe that when this motor was updated, often times the piston to cylinder clearance was on the high side or exceeded specs. Heat cause the piston to expand and many feel expand to the perfect size....on boost.
The last thing is the fact that the guy running the turbo isn't the typical non-maintenance guy that doesn't understand mechanical aptitude, non-engine warm-up, check oil every 3 rides kind of guy, runs old gas, stores sled out side during summer months. The turbo guy generally is picky, performs all of his own maintenance, and brings sled into the garage after every ride or trip and verifies sled is in optimum condition.
