Typically, an intercooler will lower boost if no other changes are made but "boost" in and of itself is not the goal, airflow and a power increase is. Sometimes, you can make MORE power with less boost just from the cooler, denser air charge. Boost is just a number! A part of a calculation! If the final answer is power and performance, you have to put many more things in the equation to get the RIGHT answer.
The primary reason why the IDIs are always limited in boost is the indirect injection and the high CR. Remember the difference between static and dynamic compression ratios. You take 21.5:1, add 10 P (or more), fire it off and you get some seriously high combustion pressures (hence the need for better gaskets and head studs for a turbo conversion). The IDIs, the NA IDIs, NEED that high CR for cold starts and low end torque characteristics. The burn rate of the fuel is slower on an IDI because combustion starts in a remote chamber and that's why the cetane rating of the fuel is a bit more important for an IDI vs a DI. IDI's generally don't breathe as well as DI and their combustion chambers are smaller (at least the parts that do the work) and fuel mixing is less efficient than DI (one reason propane isn't as effective and can be more harmful in IDI that it is in DI: IMO nitrous, an oxidizer, is a better choice for a IDI). If you look at the end of the IDI era (not just the Ford/Navistar engines) you will see only a few turbocharged engines and, invariably, they are low boost (relatively speaking... low vs DI). There were and are good engineering reasons for that and they have to do with the natural limitations of the IDI design. That doesn't mean you can't improve on an IDI engine but the limits are lower and the cost vs gain ratio is lower.
DI engines have taken over the diesel industry for a lot of (good) reasons and the performance side of that is huge as well. In these very few places devoted to old technology, you see people trying to translate DI performance tips to IDI engines. Some does but a lot doesn't. This fixation on "boost" is one of those that really doesn't fully apply... especially on an engine whose basic structure and design was designed to be NA, or low boost, and was built for low power density with a decent safety factor. Of course IH could have built an IDI engine to make more power and tolerate higher boost but they didn't. Unless we have lots of money to spend on custom improvements to the basic structure and design, we are left working around what's there. We all have differences in goals and a higher or lower tolerance for risk or a shorter engine life. Thjose are personal chjoice one hopefully makes after being fully informed. For myself, I've had this truck 28 years and it's remained more or less in one piece because I worked within it's limitations. My opinion is the various aftermarket turbo kits and the performance that went with them used up about 2/3s of the safety factor but left enough for a long working life with an owner that took some care in using the right foot.
BTW, I much prefer a non-wastegated turbo in the IDI application because of the lower backpressure and EGT. You don't get that "snap" at the low end but then I use my truck as a hauler, not a dragster.
make that 220*
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